SEARCH

SEARCH BY CITATION

Keywords:

  • cervical length measurements;
  • funneling;
  • preterm birth;
  • systematic review

Abstract

  1. Top of page
  2. Abstract
  3. Introduction
  4. Methods
  5. Results
  6. Discussion
  7. Acknowledgements
  8. References
  9. Supporting Information

This review investigates the accuracy with which transvaginal cervical sonography predicts spontaneous preterm birth. Published studies were identified without language restrictions through nine different databases and manual searching of bibliographies of known primary and review articles. Studies were selected if they undertook antenatal transvaginal sonographic cervical assessment among a population of pregnant women with known gestational age of delivery. There were 46 primary articles, which included a total of 31 577 women, consisting of 33 studies in asymptomatic and 13 studies in symptomatic women. Data were extracted for the studies' characteristics and quality. Accuracy data were used to form 2 × 2 contingency tables for various cervical length measurements with birth before 32, 34 and 37 weeks' gestation as the reference standards. Data were stratified according to singleton or twin pregnancy, gestational age at testing, cervical length threshold, and the various reference standards, and were pooled to produce summary estimates of likelihood ratios (LRs). Our review showed that transvaginal cervical sonography identifies women who are at higher risk of spontaneous preterm birth, although there was a wide variation amongst studies with respect to gestational age at testing, definition of threshold of abnormality and definition of reference standard. The most commonly reported sub-group was testing of asymptomatic women at < 20 weeks' gestation using a threshold cervical length of 25 mm with spontaneous preterm birth before 34 weeks' gestation as the reference standard. The summary LR+ for this group was 6.29 (95% CI, 3.29–12.02), with corresponding LR− of 0.79 (95% CI, 0.65–0.95). Both cervical length measurement and funneling, whether alone or in combination, appear to be useful (depending on the threshold chosen to define the abnormality) in predicting spontaneous preterm birth in asymptomatic women. For symptomatic women there was a paucity of data, although the degree of funneling appeared to be predictive of spontaneous preterm birth. Copyright © 2003 ISUOG. Published by John Wiley & Sons, Ltd.


Introduction

  1. Top of page
  2. Abstract
  3. Introduction
  4. Methods
  5. Results
  6. Discussion
  7. Acknowledgements
  8. References
  9. Supporting Information

Spontaneous preterm birth occurs before 37 weeks' gestation in 7–11% of pregnancies, and before 34 weeks' gestation in 3–7% of pregnancies1, 2. Delivery before 34 weeks' gestation, however, accounts for three-quarters of neonatal mortality and one half of long-term neurological impairment in children3. Measurement of cervical length and detection of cervical funneling have been claimed to predict the risk of preterm birth, and increasingly in clinical practice transvaginal ultrasound is being utilized to assess such risk. Transvaginal ultrasound allows clear and consistently successful visualization of the cervix and the internal os, providing an advantage over transabdominal sonographic evaluation, which may be unreliable due to maternal habitus, position of the cervix, degree of bladder filling, and the obscuring effect of the fetus. If shortened cervical length in asymptomatic women in the mid-trimester predicts spontaneous preterm birth, closer monitoring or entry into clinical intervention trials4 may be targeted at this group. In symptomatic women, if shortened cervical length could identify an impending spontaneous preterm birth before advanced cervical dilatation, antenatal steroids5, tocolytics and in-utero transfer may be used accordingly to avert adverse neonatal sequelae.

Many primary studies claim that shortened cervical length or presence of internal os funneling (dilatation) on transvaginal ultrasound predicts spontaneous preterm birth. However, due to variation in thresholds for abnormality and differences in gestational age defining preterm birth, there is heterogeneity in the estimates of accuracy. Furthermore, most published studies have concentrated on < 37 weeks' gestation preterm birth as the reference standard rather than the more clinically relevant 34 weeks' gestation or earlier. Two existing systematic reviews6, 7 of the literature have not addressed this issue. Additionally, their searches were limited, study selection was restricted by language and study quality assessment was not undertaken. These factors introduce a potential for bias in their inferences8, 9.

On this basis, we conducted a comprehensive systematic review using appropriate quality assessments and meta-analyses to obtain valid and reliable accuracy estimates of transvaginal cervical sonography in predicting spontaneous preterm birth. We took into account the clinical considerations outlined above in our systematic review in order to produce more clinically meaningful summaries.

Methods

  1. Top of page
  2. Abstract
  3. Introduction
  4. Methods
  5. Results
  6. Discussion
  7. Acknowledgements
  8. References
  9. Supporting Information

Our review was based on a prospective protocol developed using widely recommended methodology10–13.

Data sources

Our electronic searches targeted studies of all diagnostic procedures for the prediction of spontaneous preterm birth. Studies were identified from various sources without language restriction. The search included general bibliographical databases: MEDLINE (1966 to June 2002), EMBASE (1980 to June 2002), PASCAL (1973 to June 2002) and BIOSIS (1969 to June 2002). It also included specialist databases: the Cochrane Library (2002 : 2) (which includes Database of Systematic Reviews, Controlled Trial Register and Database of Abstracts of Reviews of Effectiveness), MEDION (1974 to December 2000) (a database of diagnostic test reviews set up by Dutch and Belgian researchers), National Research Register (2002 : 4), SCISEARCH (1974 to June 2002) and Conference Papers (1973 to June 2002). The electronic search strategy has been described in detail elsewhere14. Additionally, we checked reference lists of known reviews and primary articles to identify cited articles not captured by electronic searches. When accuracy data were not extractable, we attempted to contact the corresponding author, by letter or e-mail, to seek their assistance in data extraction.

Study selection

Figure 1 summarizes the literature identification and selection process. Studies were selected if the following criteria were met: 1) asymptomatic or symptomatic population of pregnant women; 2) antenatal transvaginal sonographic cervical length measurement of the cervix; 3) known gestation at spontaneous birth; 4) observational cohort design (excluding studies with case-control design). Studies were selected in two stages. Firstly, the electronic searches were scrutinized by two reviewers independently (H.H. and L.M.B.) and full manuscripts of all citations that were likely to meet the predefined selection criteria were obtained. Secondly, the final inclusion or exclusion decisions were made on assessment of these manuscripts. In cases of duplicate publications, complete data were extracted from all sources but only the most recent study is included in the review. No language restrictions were applied. English language manuscripts were assessed independently by two reviewers (H.H. and A.C.), French language manuscripts by one reviewer (L.M.B.), and other language manuscripts by people who had sufficient command of the language to allow data extraction from the manuscripts. Disagreements were resolved either by consensus or arbitration by a third reviewer (K.S.K.).

thumbnail image

Figure 1. Study selection process for systematic review of transvaginal cervical ultrasound in predicting spontaneous preterm birth.

Download figure to PowerPoint

There were 46 primary accuracy articles that met the selection criteria, consisting of 33 accuracy studies in asymptomatic and 13 studies in symptomatic women, which included a total of 31 577 women. A list of excluded primary studies (n = 116) is available as supplementary material on the Internet.

Extraction of data for analysis

Information was extracted from each selected article on study characteristics, study quality and accuracy of results. We were interested in separating asymptomatic (without uterine tightenings/contractions) and symptomatic (with uterine tightenings/contractions but before advanced cervical dilatation) women. Furthermore, as cervical length in singleton pregnancies is significantly longer than in twin pregnancies, these two populations were analyzed separately15. With respect to transvaginal sonography, we extracted data both for the various thresholds defining abnormality and for the gestational age at testing. The latter was divided into three groups: < 20 weeks' gestation, 20–24 weeks' gestation and > 24 weeks' gestation. For studies in which the reported gestational age at testing encompassed two or more of the groupings, we classified them according to their mean gestational age at testing (e.g. a study that reported gestational age at testing of 18–26 weeks' gestation would be grouped amongst studies reporting testing at 20–24 weeks' gestation).

Accuracy data were used to construct 2 × 2 tables for the various cervical lengths, funneling and gestational age at spontaneous preterm birth, which served as the reference standard. Various definitions of spontaneous preterm birth had been used as reference standard, including birth before 32, 34 and 37 weeks' gestation, reflecting their relatively different neonatal prognoses16, 17, but we focused mainly on birth before 34 weeks' gestation.

Assessment of methodological quality

We defined quality as confidence that the study design, conduct and analysis minimized bias in the estimation of test accuracy. Existing checklists10, 12, 13 and empirical evidence9 relate bias to a number of items: case-control design, non-prospective data collection, non-consecutive patient enrollment, inadequate description of population or test, lack of blinding of carer to test results, use of different reference tests, partial verification, and lack of description of the reference standard. During study selection, case-control studies were excluded from our review. Items related to reference standards were not relevant to our review, as delivery of neonates (preterm or term) was a single reference test, which was usually verifiable and indisputable. Therefore, we considered a study to be of high quality if it used a prospective design, consecutive enrollment, adequate test description, and blinding of the test result.

Data synthesis

Data from individual studies were synthesized separately for asymptomatic women with singleton and those with twin pregnancies, and for symptomatic women with singleton pregnancies. When a study based its results on mixed (singleton and twin) pregnancies, unless data were extractable separately, it was not considered for further synthesis.

Initially, our syntheses were stratified according to gestational age at testing and the three definitions of reference standard i.e. delivery before 32, 34 and 37 weeks' gestation. We included studies with spontaneous birth before 33 and 35 completed weeks' gestation into the group of studies with spontaneous birth before 34 weeks' gestation in our data synthesis because of the relatively similar neonatal prognosis. Heterogeneity was assessed separately for singleton and twin pregnancies by plotting sensitivity versus 1—specificity for the various sub-groups in the receiver–operating characteristics (ROC) curves to show the distribution of their accuracy. The areas under summary ROC curves18 were calculated and used to provide measures of overall accuracy of the various studies. A value of 1 for area under the summary ROC curve would indicate a test with perfect accuracy.

Further syntheses were stratified according to gestational age at testing, the thresholds defining abnormalities and the three reference standards. For each sub-group, likelihood ratios (LRs) with confidence intervals (CIs) were calculated and used as measures of accuracy of individual studies. Summary LRs19 were used if more than one study was included in a sub-group. Likelihood ratios indicate by how much a given test result will raise or lower the probability20 of having spontaneous preterm birth and allowed determination of post-test probabilities for various sub-groups as follows: post-test probability = LR × pre-test probability/(1 + (pre-test probability × (1–LR))).

To examine for publication and related biases, we undertook funnel plot (diagnostic odds ratio vs. 1/standard error) analysis. All statistical analyses were performed using statistical packages SPSS v. 10 (SPSS Inc., Chicago, IL, USA) and Stata 7.0 (Stata Corp., College Station, TX, USA).

Results

  1. Top of page
  2. Abstract
  3. Introduction
  4. Methods
  5. Results
  6. Discussion
  7. Acknowledgements
  8. References
  9. Supporting Information

Study characteristics and quality

Table 1 summarizes each of the selected studies' salient features according to whether the population was asymptomatic or symptomatic, and whether pregnancies were singleton or twin. Among asymptomatic women, the gestational age at testing varied from as early as 7 weeks' gestation21 to as late as 30 weeks' gestation22. The most common testing gestational age was in the late mid-trimester at 20–24 weeks. The commonest reference standard was spontaneous preterm birth around 34 weeks' gestation. The cervical length threshold for abnormality most commonly utilized was 25 mm. For asymptomatic and symptomatic singleton pregnancies, respectively, there were 87 (76 cervical lengths and 11 funneling) and 20 (11 cervical lengths and 9 funneling) 2 × 2 tables of accuracy data. For asymptomatic and symptomatic twin pregnancies, respectively, there were 44 (38 cervical lengths and 6 funneling) and 5 (3 cervical lengths and 2 funneling) 2 × 2 tables of accuracy (Tables 2 and 3).

Table 1. Characteristics of studies on accuracy of transvaginal cervical sonography in predicting spontaneous preterm birth
StudyPopulationTestReference standards
ReferenceQualitynInclusion criteriaExclusion criteriaGestational age at testing (weeks)Test threshold (mm)Presence of funneling (Yes/No). If Yes, definition of funnelingGestational age at birth
  • *

    Published abstracts.

ASYMPTOMATIC SINGLETON PREGNANCIES
Andersen et al. (1990)21Blind 113SingletonsPlacenta previa, patient thought to be at risk from cervical incompetence7–3034, 39No34 (only for 34 mm threshold), 37 weeks
Prospective       
Test described       
Andrews et al. (2000)23Blind  69Singletons, previous history of spontaneous preterm birth between 16 and 30 weeksMedical or obstetric complication, history of incompetent cervix that required cerclage, presented for antenatal care after 28 weeks< 20, 20–24 and 25–2922, 25YesWithin 14, 28 days of testing, and 35 weeks
Consecutive     Not defined 
Prospective       
Test described       
Arinami et al. (1999)28Blind 683Singletons, no medical or obstetric complication 26–2825No34, 36 weeks
Consecutive       
Prospective       
Test described       
Berghella et al. (1997)24Blind  96Singletons, previous spontaneous preterm birth, > 2 previous abortions, previous cone biopsy, Ehler–Danlos syndromeCervical cerclage, placenta previa, major fetal anomaly14–2216, 25Yes35 weeks
Consecutive     % of funneling 
Prospective       
Test described       
Bouchar et al. (1999)31Blind  50SingletonsMultiple gestations, preterm premature rupture of membranes, placenta previa, cervical cerclage13–2327Yes37 weeks
Prospective       
Test described     Dilatation of internal cervical os 
Guzman et al. (2001)32Prospective 469Singletons, previous mid-trimester loss or previous preterm birth, known uterine malformation, past history of cervical cerclage 15–20 and 21–2425Yes28, 30, 32, 34 weeks
Test described       
Hartmann et al. (1999)33Blind 815Singletons, 16 years and olderInability to be followed beyond delivery24–2910, 15, 20Yes37 weeks
Prospective     Dilatation of internal cervical os > 10, 20 mm; Cervical score of < 1 or < 2, where cervical score = cervical length − cervical dilatation 
Test described       
Hasegawa et al. (1996)26Blind 298Singletons, no medical or obstetric complication, no previous history of preterm birth 18–2230No36 weeks
Consecutive       
Prospective       
Test described       
Hasegawa et al. (1996)34Blind 729Singletons, no medical or obstetric complication 15–34Mean—1SDYes36 weeks
Prospective     Funnel index defined as ratio of funnel length over funnel length + cervical length 
Test described       
Hassan et al. (2000)35Retrospective6877Singletons 14–2410, 15, 20, 25, 30, 40No32 weeks
Heath et al. (1998)36Consecutive1252Singletons 2310, 20, 30, 40, 50, 60No32 weeks
Prospective       
Test described       
Hibbard et al. (2000)37Consecutive 760Singletons 16–2222, 27, 30No32, 35, 37 weeks
Prospective       
Test described       
Iams et al. (1996)27Blind2915SingletonsMultiple gestations, cervical cerclage, placenta previa, fetal anomaly24 and 2820, 25, 30Yes35 weeks
Consecutive     3-mm protrusion of amniotic membrane into the cervical canal 
Prospective       
Test described       
Owen et al. (2001)25Blind 183Singletons with at least one previous spontaneous preterm birthCervical cerclage, uterine anomaly, chronic medical problem which may cause iatrogenic preterm delivery16–1815, 20, 25, 30Yes35 weeks
Consecutive     Funneling not defined 
Prospective       
Test described       
Taipale and Hiilesmaa (1998)38Consecutive3694SingletonsInadequate imaging, iatrogenic preterm delivery, fetal death or malformation18–2225, 29, 35, 40, 45, 50No35, 37 weeks
Prospective       
Test described       
To et al. (2001)39Consecutive6334Singletons 22–2415Yes33 weeks
Prospective     Dilatation of internal cervical os > 5 mm 
Test described       
Tongsong et al. (1995)22Prospective 730SingletonsNo medical, fetal, or cervical problems28–3020, 25, 30, 35, 40, 45, 50, 55, 60No37 weeks
Test described       
Watson et al. (1999)40Consecutive 407Singletons, previous preterm birth, extreme maternal age, known uterine abnormalityMultiple gestations, fetal abnormality24–2815, 20, 25, 30, 35, 40, 45, 50No35 weeks
Prospective       
Test described       
ASYMPTOMATIC TWIN PREGNANCIES
*Althuisius and Dekker (1998)41  101Twins 16–3230No34 weeks
Goldenberg et al. (1996)42Blind 147TwinsCervical cerclage, placenta previa, severe fetal anomaly24–2825No32, 35, 37 weeks
Prospective       
Test described       
*Granovsky-Gisaru et al. (1998)43Prospective  43Twins 18–2930 34 weeks
Guzman et al. (2000)44Prospective 131Twins 15–20, 21–24 and 25–2820Yes28, 30, 32, 34 weeks
Test described     Funnel length and width but cut-off was not stated 
Imseis et al. (1997)45Consecutive  85TwinsCervical cerclage24–2635NoWithin 21 days of testing and 34 weeks
Prospective       
Test described       
Skentou et al. (2001)46Consecutive 434TwinsCervical cerclage22–2415, 20, 25No33 weeks
Prospective       
Test described       
Soriano et al. (2002)47Blind  44Twins, primigravidae, all from infertility treatmentIntrauterine fetal death, severe pre-eclampsia, placental abruption18–2435Yes34 weeks
Prospective     Funnel length and width of cervical internal os 
Test described       
Souka et al. (1999)48Prospective 215TwinsCervical cerclage, monochorionic twins, twin-to-twin transfusion complication22–2415, 25, 35, 45No24, 28, 30, 32 weeks
Test described       
*Weisz et al. (2000)49Consecutive  50Twins, primigravidae 18–2235No34 weeks
Prospective       
Wennerholm et al. (1997)50Blind 121Twins 24, 28 and 3225, 30, 33No35, 37 weeks
Prospective       
Test described       
Yang et al. (2000)51Consecutive  65TwinsPreterm labor, prophylactic cervical cerclage, placenta previa, induced preterm birth18–2625, 26–30, 31–35Yes32, 35, 37 weeks
Prospective     Funnel length divided by cervical length 
Test described       
MIXED POPULATIONS OR NUMBER OF FETAL GESTATIONS NOT STATED
*Allbert and Davis (1996)52Retrospective  25Women with at least one previous spontaneous preterm birthNo cerclage14–2430No37 weeks
Berghella et al. (1997)53Blind43Singletons, twins, tripletsCervical cerclage, known cervical abnormalities16–2815, 20Yes37 weeks
RetrospectiveFunnel length > 16 mm 
ProspectiveFunnel length > 25 mm 
Test describedFunnel width > 14 mm 
Funnel width > 16 mm 
% of funneling 
Dowd et al. (2001)54Prospective 316Women who attended public antenatal clinicsCervical cerclage, iatrogenic preterm delivery18, 2420, 25, 30Yes34, 37 weeks
Test described     V- or U-shaped indentation, or dilatation of internal cervical os 
*Iams et al. (1995)55Consecutive2108No previous history of mid-trimester loss or preterm birth 22–2425No35 weeks
Prospective       
SYMPTOMATIC SINGLETON PREGNANCIES
Crane et al. (1997)29Blind 136Singletons, twins, symptomatic women whose contraction had been arrested by tocolyticsCervical dilatation > 3 cm, more than twin pregnancies, placenta previa, ruptured membrane23–3330YesMean number of days to delivery, mean gestational age at delivery and 34, 37 weeks
Consecutive     V- or U-shaped indentation of cervical canal by amniotic membrane on application of suprapubic pressure 
Prospective       
Test described       
Goffinet et al. (1997)56Prospective 108SingletonsCervical cerclage, pre-labor premature rupture of membrane, cervical dilatation > 2 cm, iatrogenic preterm delivery24–3426NoWithin 21 days of testing and 37 weeks
Test described       
Gomez et al. (1994)30Blind  59SingletonsPre-labor premature rupture of membrane, cervix dilatation > 3 cm21–3518Yes36 weeks
Consecutive     Funnel width > 6 mm 
Prospective     Funnel length > 9 mm 
Test described     Any funneling 
Murakawa et al. (1993)57Prospective  32SingletonsSuspicion of cervical incompetence25–3520, 25, 30, 35No37 weeks
Test described       
Okitsu et al. (1992)58Prospective 130SingletonsPlacenta previa24–36Mean—1.5 SDYes36 weeks
Test described     Dilatation of internal cervical os > 5 mm 
Onderoglu (1997)59Blind  90Singletons, intact membrane, cervical dilatation < 3 cm, absence of fetal and maternal complications 25–3628No37 weeks
Rageth et al. (1997)60Retrospective  61SingletonsMultiple gestations, intrauterine growth restriction, pre-eclampsia, diabetes25–3530No35 weeks
Rizzo et al. (1996)61Prospective 108Singletons, intact membrane, cervical dilatation < 3 cm, absence of maternal or fetal complication 24–3620Yes37 weeks
Test described     Dilatation of internal cervical os > 5 mm 
Vendittelli et al. (2001)62Blind 174SingletonsCervical dilatation > 3 cm, pre-labor premature rupture of membranes, cervical cerclage, active vaginal bleeding, known fetal malformation or death, placenta previa18–3630Yes37 weeks
Prospective     V- or U-shaped indentation of the cervical internal os 
Test described       
SYMPTOMATIC TWIN PREGNANCIES
Crane et al. (1997)29Blind  26Singletons, twins, symptomatic women whose contraction had been arrested by tocolyticsAdvanced labor, cervical dilatation > 3 cm, more than twin pregnancies, placenta previa, ruptured membrane23–3330YesMean number of days to delivery, mean gestational age at delivery and 34, 37 weeks
Consecutive     V- or U-shaped indentation of cervical canal by amniotic membrane on application of suprapubic pressure 
Prospective       
Test described       
*Persutte et al. (2000)63Consecutive 105Twins 20–3225No37 weeks
Prospective       
Vendittelli et al. (2001)62Blind  26TwinsCervical dilatation > 3 cm, premature rupture of membrane, cervical cerclage, active vaginal bleeding, known fetal malformation or death, placenta previa18–3630Yes37 weeks
Prospective     V- or U-shaped indentation of the cervical internal os 
Test described       
MIXED POPULATIONS OR NUMBER OF FETAL GESTATIONS NOT STATED
Benham et al. (2002)64Retrospective37Singletons, twins, triplets 16–2425Yes34 weeks
Internal cervical os dilatation and > 25% prolapse of membrane into the cervical canal but not exceeding the external cervical os 
Iams et al. (1994)65Prospective  60Singletons, twins, after successful tocolytic treatmentMultiple gestations (more than twins), unsuccessful tocolytic treatment, cervical cerclage, pre-labor premature rupture of membranes24–3430NoWithin 21 days of testing and 36, 37 weeks
Test described       
*Solomon and Carlson (1995)66Blind  23 Cervical dilatation > 1 cm20–3430No37 weeks
Table 2. Individual and pooled likelihood ratios* for predicting spontaneous preterm birth for a range of thresholds for cervical length measurements among various population sub-groups tested at different gestational ages
Sub-groups, testing gestational age, & thresholdsSpontaneous preterm birth before
32 weeks' gestation34 weeks' gestation37 weeks' gestation
nLR + (95% CI)LR − (95% CI)nLR + (95% CI)LR − (95% CI)nLR + (95% CI)LR − (95% CI)
  • *

    Pooling was performed using a random effects model.

  • Includes: among asymptomatic singleton pregnancies, one study of 33 weeks' gestation and seven of 35 weeks' gestation; among asymptomatic twin pregnancies, two studies of 35 weeks' gestation; and among symptomatic singleton pregnancies, two studies of 35 weeks' gestation.

  • Indicates statistical heterogeneity at P < 0.05. n, number of studies.

ASYMPTOMATIC SINGLETON PREGNANCIES
< 20 weeks
 15 mm   130.53 (1.72–542.05)0.90 (0.81–0.99)   
 20 mm18.21 (5.32–12.66)0.45 (0.27–0.77)114.47 (1.73–120.69)0.90 (0.81–0.99)   
 22 mm19.05 (3.55–23.08)0.83 (0.69–1.00)19.56 (4.68–19.50)0.80 (0.69–0.93)18.74 (3.82–19.96)0.88 (0.81–0.96)
 25 mm24.10 (1.67–10.11)0.75 (0.52–1.08)56.29 (3.29–12.02)0.79 (0.65–0.95)   
 27 mm17.01 (3.56–13.77)0.73 (0.57–0.94)18.34 (4.70–14.80)0.73 (0.61–0.87)15.87 (3.27–10.53)0.83 (0.744–0.92)
 30 mm23.67 (2.99–4.50)0.73 (0.61–0.87)22.84 (1.10–7.35)0.75 (0.57–0.98)13.77 (2.55–5.56)0.73 (0.63–0.85)
 34 mm   12.98 (1.50–5.92)0.63 (0.40–0.99)   
 39 mm      11.76 (1.26–2.44)0.61 (0.23–1.64)
 40 mm11.59 (1.54–1.64)0.06 (0.03–0.15)      
20–24 weeks         
 10 mm151.92 (23.05–116.91)0.58 (0.40–0.86)      
 15 mm   127.92 (18.59–41.92)0.65 (0.54–0.79)   
 16 mm   14.65 (1.51–14.29)0.75 (0.55–1.03)   
 20 mm   17.64 (5.21–11.20)0.79 (0.72–0.87)   
 22 mm   14.51 (1.15–17.64)0.74 (0.51–1.08)   
 25 mm24.19 (2.63–6.70)0.40 (0.18–0.88)34.40 (3.53–5.49)0.67 (0.59–0.76)125.61 (8.55–76.72)0.95 (0.90–0.99)
 27 mm      121.27 (5.14–88.03)0.47 (0.29–0.74)
 29 mm   16.82 (3.24–14.33)0.83 (0.70–0.99)15.98 (3.56–10.04)0.86 (0.79–0.95)
 30 mm11.84 (1.35–2.52)0.50 (0.26–0.98)12.28 (1.91–2.71)0.60 (0.50–0.73)   
 35 mm   11.69 (1.14–2.50)0.75 (0.54–1.03)11.32 (0.99–1.76)0.88 (0.76–1.03)
 40 mm11.23 (1.10–1.37)0.23 (0.03–1.56)11.24 (0.95–1.61)0.74 (0.46–1.19)11.16 (0.97–1.38)0.83 (0.64–1.07)
 45 mm   11.24 (1.13–1.36)0.26 (0.07–1.01)11.17 (1.08–1.26)0.47 (0.26–0.84)
 50 mm11.06 (1.04–1.07)0.45 (0.03–7.02)11.10 (1.09–1.12)0.17 (0.01–2.59)11.09 (1.07–1.12)0.12 (0.02–0.84)
 60 mm11.01 (1.00–1.01)3.25 (0.20–53.90)      
> 24 weeks         
 10 mm      13.39 (1.56–12.1)0.94 (0.88–0.98)
 15 mm   17.08 (1.64–30.47)0.93 (0.85–1.02)12.00 (1.36–3.71)0.92 (0.85–0.97)
 20 mm   25.83 (4.14–8.14)0.81 (0.64–1.01)21.21 (0.90–1.64)0.96 (0.90–1.03)
 22 mm   12.67 (1.79–3.98)0.27 (0.0.2–3.40)   
 25 mm   44.07 (3.17–5.24)0.62 (0.43–0.90)13.19 (1.13–8.98)0.96 (0.91–1.01)
 30 mm   22.70 (1.94–3.77)0.52 (0.29–0.94)12.49 (1.72–3.61)0.79 (0.69–0.91)
 35 mm   12.20 (1.56–3.10)0.61 (0.43–0.86)11.76 (1.47–2.11)0.54 (0.41–0.73)
 40 mm   11.50 (1.16–1.95)0.63 (0.41–0.96)11.07 (0.96–1.20)0.77 (0.49–1.21)
 45 mm   11.20 (0.99–1.45)0.64 (0.36–1.16)11.04 (0.99–1.10)0.60 (0.25–1.44)
 50 mm   12.09 (1.77–2.30)0.10 (0.03–0.37)11.01 (0.99–1.04)0.44 (0.06–3.27)
 55 mm      11.01 (1.00–1.01)0.77 (0.04–14.24)
ASYMPTOMATIC TWIN PREGNANCIES
< 20 weeks         
 20 mm   159.89 (3.46–103.48)0.71 (0.52–0.96)   
20–24 weeks         
 15 mm19.32 (2.76–31.49)0.78 (0.60–1.02)17.60 (2.09–27.67)0.89 (0.81–0.97)   
 20 mm12.75 (1.25–6.09)0.69 (0.42–1.12)24.54 (1.46–14.14)0.75 (0.64–0.90)   
 25 mm25.04 (3.22–7.89)0.56 (0.40–0.77)45.02 (3.31–7.61)0.75 (0.54–1.06)22.71 (1.28–5.75)0.85 (0.76–0.95)
 30 mm   42.31 (1.08–4.93)0.69 (0.91–1.17)   
 35 mm21.55 (0.79–3.04)0.72 (0.29–1.83)11.47 (1.09–1.97)0.88 (0.69–1.12)11.67 (0.49–5.71)1.17 (0.95–1.44)
 45 mm11.14 (0.99–1.30)0.34 (0.05–0.81)21.12 (1.00–1.26)0.45 (0.15–1.40)   
> 24 weeks         
 20 mm12.31 (1.18–4.53)0.59 (0.28–1.22)13.44 (2.05–5.78)0.41 (0.21–0.80)   
 25 mm   31.82 (1.26–2.63)0.83 (0.72–0.95)21.89 (1.26–2.85)0.73 (0.62–0.88)
 30 mm   22.11 (1.43–3.12)0.61 (0.42–0.87)   
 35 mm   21.84 (1.48–2.29)0.29 (0.08–1.09)   
SYMPTOMATIC SINGLETON PREGNANCIES
> 20 weeks         
 18 mm      13.36 (1.73–6.54)0.35 (0.17–0.70)
 20 mm      112.83 (0.72–228.3)0.73 (0.51–1.04)
 25 mm      14.45 (1.43–13.91)0.42 (0.19–0.95)
 26 mm      12.38 (1.65–3.42)0.31 (0.14–0.69)
 28 mm      14.53 (2.50–8.20)0.26 (0.14–0.51)
 30 mm   21.98 (1.55–2.50)0.28 (0.08–0.80)32.15 (1.51–3.06)0.32 (0.21–0.48)
 35 mm      11.50 (1.11–2.03)0.12 (0.01–1.96)
SYMPTOMATIC TWIN PREGNANCIES
> 20 weeks         
 25 mm      12.16 (1.07–4.37)0.69 (0.52–0.91)
 30 mm   12.33 (1.42–3.82)0.15 (0.01–2.14)21.30 (0.89–1.90)0.50 (0.20–1.27)
Table 3. Individual and pooled* likelihood ratios for predicting spontaneous preterm birth in the presence of cervical funneling (any description) among various population sub-groups tested at different gestational ages
Sub-groups, testing gestational age, & thresholdsSpontaneous preterm birth before
32 weeks' gestation34 weeks' gestation37 weeks' gestation
nLR + (95% CI)LR − (95% CI)nLR + (95% CI)LR − (95% CI)nLR + (95% CI)LR − (95% CI)
  • *

    Pooling was performed using a random effects model.

  • Includes: among asymptomatic singleton pregnancies, one study of 33 weeks' gestation and seven of 35 weeks' gestation; among asymptomatic twin pregnancies, two studies of 35 weeks' gestation; and among symptomatic singleton pregnancies, two studies of 35 weeks' gestation.

  • Additional definitions of funneling: 1Percentage of funneling = [Funnel width/(funnel length + cervical length)] × 100%; 2Percentage of funneling = [Funnel length/(funnel length + cervical length)] × 100%; 3V- or U-shaped indentation of cervical canal by amniotic membrane on application of suprapubic pressure; 4Cervical index = (Funnel length + 1)/cervical canal length; 5Cervical score = Cervical length − cervical dilatation. n, number of studies.

ASYMPTOMATIC SINGLETON PREGNANCIES
< 20 weeks
 Presence of funneling   126.81 (1.57–457.07)0.67 (0.47–0.95)   
20–24 weeks
 Dilatation of cervical internal os > 5 mm   17.97 (5.14–12.35)0.75 (0.65–0.88)   
 Presence of funneling   13.10 (1.69–5.67)0.51 (0.29–0.91)   
 < 25% funneling1   11.03 (0.24–4.36)1.00 (0.82–1.21)   
 25–50% funneling1   121.44 (5.08–90.51)0.48 (0.29–0.80)   
 > 50% funneling1   193.33 (5.73–1520.44)0.41 (0.23–0.73)   
> 24 weeks
 Presence of funneling   13.11 (1.55–6.23)0.30 (0.09–1.02)   
 Dilatation of cervical internal os > 5 mm      13.81 (2.22–6.56)0.84 (0.75–0.94)
 Dilatation of cervical internal os > 10 mm      14.36 (1.73–10.99)0.94 (0.87–1.00)
 Cervical score < 25      12.38 (1.43–3.96)0.87 (0.77–0.98)
 Cervical score < 15      13.05 (0.86–10.83)0.97 (0.93–1.02)
ASYMPTOMATIC TWIN PREGNANCIES
20–24 weeks
 Funneling2129.50 (3.61–241.28)0.51 (0.23–1.13)110.00 (1.12–89.21)0.82 (0.63–1.05)111.10 (0.62–198.09)0.86 (0.75–1.00)
 50% funneling2142.86 (2.28–805.60)0.67 (0.38–1.17)115.94 (0.81–315.02)0.86 (0.75–1.00)16.17 (0.31–123.61)0.93 (0.84–1.03)
SYMPTOMATIC SINGLETON PREGNANCIES
 Funneling3   14.70 (1.90–11.66)0.61 (0.34–1.10)   
 Funneling3      12.53 (1.02–6.25)0.86 (0.71–1.04)
 Funnel width − 6 mm      12.75 (1.40–5.40)0.44 (0.23–0.83)
 Funnel length − 9 mm      17.86 (2.58–23.90)0.31 (0.16–0.62)
 Cervical index4 > 0.5      24.74 (2.87–7.81)0.33 (0.22–0.49)
 Presence of funneling      11.68 (1.11–2.55)0.42 (0.18–0.96)
 Dilatation of cervical internal os > 5 mm      22.27 (1.64–3.15)0.42 (0.27–0.64)
SYMPTOMATIC TWIN PREGNANCIES
 Funneling3   14.20 (1.18–14.94)0.47 (0.16–1.38)11.17 (0.29–4.74)0.95 (0.62–1.46)

The methodological quality of the included primary studies is summarized in Figure 2. Eight (23%) studies, six among asymptomatic women with singleton pregnancies23–28 and two among symptomatic women with singleton pregnancies29, 30, fulfilled all four criteria for high quality.

thumbnail image

Figure 2. Methodological quality of the 46 studies included in the systematic review. Data presented as 100% stacked bars. Figures in the stacks represent number of studies.

Download figure to PowerPoint

Accuracy of transvaginal sonography in asymptomatic women

As shown in Table 2, transvaginal sonographic cervical length measurement had variable LRs for positive and negative test results depending on the thresholds used for defining abnormalities and gestational age at testing. The variability of the accuracy for different studies was also reflected in the distribution of studies, stratified according to the gestational age at testing, in the summary ROC space (Figure 3). The area under the summary ROC curve was 0.80 (95% CI, 0.69–0.91) for singleton pregnancies and 0.67 (95% CI, 0.55–0.79) for twin pregnancies. Prediction of spontaneous preterm birth was more accurate among studies testing at < 20 weeks' gestation using smaller cervical length thresholds (Table 2). These trends were similar for both singleton and twin pregnancies. The LRs for positive test results were statistically homogeneous within the various sub-groups (except for one result in twin pregnancies, Table 2), while some of the LRs for negative test results showed statistical heterogeneity (Tables 2 and 4). The most commonly reported sub-group was testing of asymptomatic women at < 20 weeks' gestation using a cervical length threshold of 25 mm with spontaneous preterm birth before 34 weeks' gestation as the reference standard. The summary LR+ for this group was 6.29 (95% CI, 3.29–12.02), which would translate the 4.1% pre-test probability to a post-test probability of 15.8% (95% CI, 13.1–19.0) (Figure 4). The corresponding LR− was 0.79 (95% CI, 0.65–0.95).

thumbnail image

Figure 3. Distribution of sensitivity and 1—specificity in the summary receiver–operating characteristics space of sonographic cervical length for singleton (a) and twin (b) pregnancies to predict spontaneous preterm birth before 34 weeks' gestation. Figures for various test thresholds (not shown) are sub-grouped according to gestational age at testing. Gestational age at testing: ▪, < 20 weeks; ∇, 20–24 weeks; +, > 24 weeks.

Download figure to PowerPoint

thumbnail image

Figure 4. Pooled estimates of likelihood ratios for predicting spontaneous preterm birth at 34 weeks' gestation using 25 mm cervical length threshold measured by transvaginal sonography and their associated post-test probabilities.

Download figure to PowerPoint

Table 4. Individual and pooled* likelihood ratios from high quality studies for predicting spontaneous preterm birth for a range of thresholds for cervical length measurements among various population sub-groups tested at different gestational ages
Sub-groups, testing gestational age, & thresholdsSpontaneous preterm birth before
32 weeks' gestation34 weeks' gestation37 weeks' gestation
nLR + (95% CI)LR − (95% CI)nLR + (95% CI)LR − (95% CI)nLR + (95% CI)LR − (95% CI)
  • *

    Pooling was performed using a random effects model.

  • Some results may also have been shown in Table 2.

  • Indicates statistical heterogeneity at P < 0.05.

ASYMPTOMATIC SINGLETON PREGNANCIES
< 20 weeks
 15 mm130.53 (1.72–542.05)0.90 (0.81–0.99)   
 20 mm114.47 (1.73–120.69)0.90 (0.81–0.99)   
 22 mm19.56 (4.68–19.50)0.80 (0.69–0.93)   
 25 mm35.95 (2.39–14.83)0.70 (0.51–0.96)   
 30 mm22.00 (1.21–3.29)0.82 (0.68–0.99)   
20–24 weeks
 16 mm14.65 (1.51–14.29)0.75 (0.55–1.03)   
 20 mm17.64 (5.21–11.20)0.79 (0.72–0.87)   
 22 mm14.51 (1.15–17.64)0.74 (0.51–1.08)   
 25 mm34.40 (3.53–5.49)0.67 (0.59–0.76)   
 30 mm 2.28 (1.91–2.71)0.60 (0.50–0.73)   
> 24 weeks
 20 mm15.90 (4.12–8.45)0.73 (0.63–0.84)   
 25 mm34.07 (2.90–5.71)0.54 (0.39–0.76)   
 30 mm 2.22 (1.90–2.59)0.44 (0.32–0.61)   
SYMPTOMATIC SINGLETON PREGNANCIES
> 20 weeks
 18 mm   13.36 (1.73–6.54)0.35 (0.17–0.70)
 30 mm11.88 (1.36–2.59)0.35 (0.17–0.70)12.29 (1.68–3.12)0.29 (0.15–0.58)
 35 mm   11.50 (1.11–2.03)0.12 (0.01–1.96)
SYMPTOMATIC TWIN PREGNANCIES
> 20 weeks
 30 mm12.33 (1.42–3.82)0.15 (0.01–2.14)11.07 (0.65–1.76)0.83 (0.23–2.97)

For cervical funneling, as shown in Table 3, the larger the funneling the more accurate it was in predicting spontaneous preterm birth. Table 4 shows individual and pooled LRs based on high-quality studies23–28, which are generally in agreement with those based on both high- and lower quality studies (Table 2). In Figure 4, we demonstrate the use of LRs to generate post-test probabilities for the various gestational ages at testing when 25 mm cervical length was selected as the threshold defining abnormality.

Accuracy of transvaginal ultrasonography in symptomatic women

As shown in Table 2, transvaginal sonographic cervical length measurement also displayed variable LRs for positive and negative test results depending on the thresholds used for defining abnormalities and gestational age at testing. In this group of women, the degree of funneling appeared to be predictive of spontaneous preterm birth (Table 3). However, there was a paucity of studies assessing the accuracy of cervical sonography in predicting spontaneous preterm birth in symptomatic women.

Funnel plot analysis did not show any evidence of asymmetry for the main outcome to indicate evidence of publication and related biases.

Discussion

  1. Top of page
  2. Abstract
  3. Introduction
  4. Methods
  5. Results
  6. Discussion
  7. Acknowledgements
  8. References
  9. Supporting Information

Our systematic review showed that transvaginal cervical sonography identifies women who are at higher risk of spontaneous preterm birth. However, there was a wide variation amongst studies with respect to gestational age at testing, definition of threshold for abnormality and definition of reference standard that has an effect on the accuracy of transvaginal sonography in predicting spontaneous preterm birth. The most commonly reported sub-group was testing of asymptomatic women at < 20 weeks' gestation using a cervical length threshold of 25 mm with spontaneous preterm birth before 34 weeks' gestation as the reference standard. Both cervical length measurement and funneling, whether used alone or in combination, appear to be useful (depending on the threshold chosen to define abnormality) in predicting spontaneous preterm birth among asymptomatic women. For symptomatic women, however, there was a paucity of test accuracy studies of transvaginal sonographic cervical assessment in predicting spontaneous preterm birth. Within this limitation, in this sub-group of the population, the degree of funneling appeared to be predictive of spontaneous preterm birth.

The strength of our inferences depends upon the rigor of our methodology and the reliability of our accuracy estimates. We did not limit our search to a single database6, nor did we apply language restrictions7. Consequently, our review contained more studies compared with these previous reviews, even when considering the number of primary studies that have since been published. Mindful that reviews of test accuracy studies are fraught with difficulty due to poor methodological quality of the primary studies, we scrutinized the selected studies for their quality. Methodological issues that have empirically been shown to overestimate accuracy, such as case-control design, absence of test descriptions and the use different reference tests9, were generally not applicable to the studies we selected for review. Assessment of heterogeneity and exploration for reasons behind heterogeneity were planned a priori. In our collection of relatively higher quality studies (after excluding case-control studies), quality did not provide an explanation for variation in accuracy among sub-groups of studies based on gestational age at testing, test thresholds and reference standards. Because we were not able to explain the heterogeneous results for some of the pooled LRs, these would need to be interpreted with caution. Additionally, the power of our analyses was restricted due to the small number of studies within each sub-group.

Nevertheless, this review represents the best available estimates of risks at the time of writing. With the provision of individual threshold estimates stratified according to common testing gestational ages, clinicians should be able to make informed and explicit decisions based on more realistic probabilities generated by transvaginal sonographic measurement of cervical length with regard to the risk of spontaneous preterm birth. These estimates should also allow researchers to target randomization at high-risk patients when evaluating the effectiveness of interventions to prevent spontaneous preterm birth.

Acknowledgements

  1. Top of page
  2. Abstract
  3. Introduction
  4. Methods
  5. Results
  6. Discussion
  7. Acknowledgements
  8. References
  9. Supporting Information

This project and H. H. are funded by WellBeing charity grant no.: K2/00. The rest of the authors are employed full time by their respective institutions. We would like to thank Steven Duffy at the National Health Service Centre for Reviews and Dissemination in York, UK for his contribution to the database searches, and Dr P. J. Thompson for his critical review, comments and suggestions for improving the clarity of the manuscript.

References

  1. Top of page
  2. Abstract
  3. Introduction
  4. Methods
  5. Results
  6. Discussion
  7. Acknowledgements
  8. References
  9. Supporting Information
  • 1
    Martin JA, Hamilton BE, Ventura SJ, Menacker F, Park MM, Sutton PD. Births: final data for 2002. Natl Vital Stat Rep 2002; 51: 1102.
  • 2
    Maternal and Child Health Research Consortium (MCHRC). Confidential Enquiries into Stillbirths and Deaths in Infancy (CESDI): 6th Annual Report. MCHRC: London, 1997.
  • 3
    Paneth NS. The problem of low birth weight. Future Child 1995; 5: 1934.
  • 4
    Final report of the Medical Research Council/Royal College of Obstetricians and Gynaecologists multicentre randomised trial of cervical cerclage. MRC/RCOG Working Party on Cervical Cerclage. Br J Obstet Gynaecol 1993; 100: 516523.
  • 5
    Crowley P. Prophylactic corticosteroids for preterm birth. The Cochrane Library, Issue 3, 2002. http://www.update-software.com. [Accessed 20 May 2003].
  • 6
    Vendittelli F, Volumenie JL. Transvaginal ultrasonography examination of the uterine cervix in hospitalised women undergoing preterm labour. Eur J Obstet Gynecol Reprod Biol 2000; 90: 311.
  • 7
    Leitich H, Brunbauer M, Kaider A, Egarter C, Husslein P. Cervical length and dilatation of the internal cervical os detected by vaginal ultrasonography as markers for preterm delivery: A systematic review. Am J Obstet Gynecol 1999; 181: 14651472.
  • 8
    Song F, Khan KS, Dinnes J, Sutton AJ. Asymmetric funnel plots and publication bias in meta-analyses of diagnostic accuracy. Int J Epidemiol 2002; 31: 8895.
  • 9
    Lijmer JG, Mol BW, Heisterkamp S, Bonsel GJ, Prins MH, van der Meulen JH, Bossuyt PM. Empirical evidence of design-related bias in studies of diagnostic tests. JAMA 1999; 282: 10611066.
  • 10
    Cochrane Methods Working Group on Systematic Reviews of Screening and Diagnostic Tests. Screening and diagnostic tests: Recommended methods. 1996. http://www.cochrane.org/cochrane/sadt.htm. [Accessed 16 November 2002].
  • 11
    Honest H, Khan KS. Systematic reviews of test accuracy studies in reproductive health. WHO Reproductive Health Library (No.5) 2002; WHO/RHR/02.1.
  • 12
    Khan KS, Dinnes J, Kleijnen J. Systematic reviews to evaluate diagnostic tests. Eur J Obstet Gynecol Reprod Biol 2001; 95: 611.
  • 13
    Irwig L, Tosteson AN, Gatsonis C, Lau J, Colditz G, Chalmers TC, Mosteller F. Guidelines for meta-analyses evaluating diagnostic tests. Ann Intern Med 1994; 120: 667676.
  • 14
    Honest H, Bachmann LM, Khan K. Electronic searching of the literature for systematic reviews of screening and diagnostic tests for preterm birth. Eur J Obstet Gynecol Reprod Biol 2003; 107: 1923.
  • 15
    Kushnir O, Izquierdo LA, Smith JF, Blankstein J, Curet LB. Transvaginal sonographic measurement of cervical length. Evaluation of twin pregnancies. J Reprod Med 1995; 40: 380382.
  • 16
    Macones GA, Bader TJ, Asch DA. Optimising maternal-fetal outcomes in preterm labour: a decision analysis. Br J Obstet Gynaecol 1998; 105: 541550.
  • 17
    Seubert DE, Stetzer BP, Wolfe HM, Treadwell MC. Delivery of the marginally preterm infant: what are the minor morbidities? Am J Obstet Gynecol 1999; 181: 10871091.
  • 18
    Moses LE, Shapiro D, Littenberg B. Combining independent studies of a diagnostic test into a summary ROC curve: data-analytic approaches and some additional considerations. Stat Med 1993; 12: 12931316.
  • 19
    Petitti DB. Meta-analysis, decision analysis, and cost-effectiveness analysis. Oxford University Press: Oxford, 1994.
  • 20
    Jaeschke R, Guyatt GH, Sackett DL. Users' guides to the medical literature. III. How to use an article about a diagnostic test. B. What are the results and will they help me in caring for my patients? The Evidence-Based Medicine Working Group. JAMA 1994; 271: 703707.
  • 21
    Andersen HF, Nugent CE, Wanty SD, Hayashi RH. Prediction of risk for preterm delivery by ultrasonographic measurement of cervical length. Am J Obstet Gynecol 1990; 163: 859867.
  • 22
    Tongsong T, Kamprapanth P, Srisomboon J, Wanapirak C, Piyamongkol W, Sirichotiyakul S. Single transvaginal sonographic measurement of cervical length early in the third trimester as a predictor of preterm delivery. Obstet Gynecol 1995; 86: 184187.
  • 23
    Andrews WW, Copper R, Hauth JC, Goldenberg RL, Neely C, Dubard M. Second-trimester cervical ultrasound: associations with increased risk for recurrent early spontaneous delivery. Obstet Gynecol 2000; 95: 222226.
  • 24
    Berghella V, Tolosa JE, Kuhlman K, Weiner S, Bolognese RJ, Wapner RJ. Cervical ultrasonography compared with manual examination as a predictor of preterm delivery. Am J Obstet Gynecol 1997; 177: 723730.
  • 25
    Owen J, Yost N, Berghella V, Thom E, Swain M, Dildy GA 3rd, Miodovnik M, Langer O, Sibai B, McNellis D. National Institute of Child Health and Human Development, Maternal-Fetal Medicine Units Network. Mid-trimester endovaginal sonography in women at high risk for spontaneous preterm birth. JAMA 2001; 286: 13401348.
  • 26
    Hasegawa I, Tanaka K, Takahashi K, Tanaka T, Aoki K, Torii Y, Okai T, Saji F, Takahashi T, Sato K, Fujimura M, Ogawa Y. A prospective clinical study for the prediction of preterm delivery in a low risk population. J Matern Fetal Invest 1996; 6: 148151.
  • 27
    Iams JD, Goldenberg RL, Meis PJ, Mercer BM, Moawad A, Das A, Thom E, McNellis D, Copper RL, Johnson F, Roberts JM. The length of the cervix and the risk of spontaneous premature delivery. National Institute of Child Health and Human Development Maternal Fetal Medicine Unit Network. N Engl J Med 1996; 334: 567572.
  • 28
    Arinami Y, Hasegawa I, Takakuwa K, Tanaka K. Prediction of preterm delivery by combined use of simple clinical tests. J Matern Fetal Med 1999; 8: 7073.
  • 29
    Crane JM, Van den HM, Armson BA, Liston R. Transvaginal ultrasound in the prediction of preterm delivery: singleton and twin gestations. Obstet Gynecol 1997; 90: 357363.
  • 30
    Gomez R, Galasso M, Romero R, Mazor M, Sorokin Y, Goncalves L, Treadwell M. Ultrasonographic examination of the uterine cervix is better than cervical digital examination as a predictor of the likelihood of premature delivery in patients with preterm labor and intact membranes. Am J Obstet Gynecol 1994; 171: 956964.
  • 31
    Bouchar S, Girard J, Dehavay P, Hautecoeur W, Blondel S. Role de la mesure du col uterin par echographie endovaginale dans le depistage de l'accouchement premature. Bulletin de la Societe clinique du CHU de Charleroi 1999; 50: 166172.
  • 32
    Guzman ER, Walters C, Ananth CV, O'Reilly-Green C, Benito CW, Palermo A, Vintzileos AM. A comparison of sonographic cervical parameters in predicting spontaneous preterm birth in high-risk singleton gestations. Ultrasound Obstet Gynecol 2001; 18: 204210.
  • 33
    Hartmann K, Thorp JM Jr, McDonald TL, Savitz DA, Granados JL. Cervical dimensions and risk of preterm birth: a prospective cohort study. Obstet Gynecol 1999; 93: 504509.
  • 34
    Hasegawa I, Tanaka K, Takahashi K, Tanaka T, Aoki K, Torii Y, Okai T, Saji F, Takahashi T, Sato K, Fujimura M, Ogawa Y. Transvaginal ultrasonographic cervical assessment for the prediction of preterm delivery. J Matern Fetal Med 1996; 5: 305309.
    Direct Link:
  • 35
    Hassan SS, Romero R, Berry SM, Dang K, Blackwell SC, Treadwell MC, Wolfe HM. Patients with an ultrasonographic cervical length < or = 15 mm have nearly a 50% risk of early spontaneous preterm delivery. Am J Obstet Gynecol 2000; 182: 14581467.
  • 36
    Heath VC, Southall TR, Souka AP, Elisseou A, Nicolaides KH. Cervical length at 23 weeks of gestation: prediction of spontaneous preterm delivery. Ultrasound Obstet Gynecol 1998; 12: 312317.
  • 37
    Hibbard JU, Tart M, Moawad AH. Cervical length at 16–22 weeks' gestation and risk for preterm delivery. Obstet Gynecol 2000; 96: 972978.
  • 38
    Taipale P, Hiilesmaa V. Sonographic measurement of uterine cervix at 18–22 weeks' gestation and the risk of preterm delivery. Obstet Gynecol 1998; 92: 902907.
  • 39
    To MS, Skentou C, Liao AW, Cacho A, Nicolaides KH. Cervical length and funneling at 23 weeks of gestation in the prediction of spontaneous early preterm delivery. Ultrasound Obstet Gynecol 2001; 18: 200203.
  • 40
    Watson WJ, Stevens D, Welter S, Day D. Observations on the sonographic measurement of cervical length and the risk of premature birth. J Matern Fetal Med 1999; 8: 1719.
  • 41
    Althuisius SM, Dekker GA. Short cervical length predicts preterm delivery in twin gestations. Am J Obstet Gynecol 1998; 178: S194.
  • 42
    Goldenberg RL, Iams JD, Miodovnik M, Van Dorsten JP, Thurnau G, Bottoms S, Mercer BM, Meis PJ, Moawad AH, Das A, Caritis SN, McNellis D. The preterm prediction study: risk factors in twin gestations. National Institute of Child Health and Human Development Maternal-Fetal Medicine Units Network. Am J Obstet Gynecol 1996; 175: 10471053.
  • 43
    Granovsky-Gisaru S, Farine D, Barrett J, van Eyk N, Ryan G, Seaward PGR, Windrim R. Is a single ultrasound measurement of cervical length a predictor of the risk of preterm delivery in multifetal pregnancy? Am J Obstet Gynecol 1998; 178: S191.
  • 44
    Guzman ER, Walters C, O'Reilly-Green C, Kinzler WL, Waldron R, Nigam J, Vintzileos AM. Use of cervical ultrasonography in prediction of spontaneous preterm birth in twin gestations. Am J Obstet Gynecol 2000; 183: 11031107.
  • 45
    Imseis HM, Albert TA, Iams JD. Identifying twin gestations at low risk for preterm birth with a transvaginal ultrasonographic cervical measurement at 24 to 26 weeks' gestation. Am J Obstet Gynecol 1997; 177: 11491155.
  • 46
    Skentou C, Souka AP, To MS, Liao AW, Nicolaides KH. Prediction of preterm delivery in twins by cervical assessment at 23 weeks. Ultrasound Obstet Gynecol 2001; 17: 710.
  • 47
    Soriano D, Weisz B, Seidman DS, Chetrit A, Schiff E, Lipitz S, Achiron R. The role of sonographic assessment of cervical length in the prediction of preterm birth in primigravidae with twin gestation conceived after infertility treatment. Acta Obstet Gynecol Scand 2002; 81: 3943.
  • 48
    Souka AP, Heath V, Flint S, Sevastopoulou I, Nicolaides KH. Cervical length at 23 weeks in twins in predicting spontaneous preterm delivery. Obstet Gynecol 1999; 94: 450454.
  • 49
    Weisz B, Soriano D, Seidman DS, Schiff E, Lipitz S, Achiron R. Risk factors for preterm birth in primigravidae with twin gestation and the role of transvaginal ultrasonographic assessment of the cervix. Am J Obstet Gynecol 2000; 182: S115.
  • 50
    Wennerholm UB, Holm B, Mattsby-Baltzer I, Nielsen T, Platz-Christensen J, Sundell G, Hosseini N, Hagberg H. Fetal fibronectin, endotoxin, bacterial vaginosis and cervical length as predictors of preterm birth and neonatal morbidity in twin pregnancies. Br J Obstet Gynaecol 1997; 104: 13981404.
  • 51
    Yang JH, Kuhlman K, Daly S, Berghella V. Prediction of preterm birth by second trimester cervical sonography in twin pregnancies. Ultrasound Obstet Gynecol 2000; 15: 288291.
  • 52
    Allbert J, Davis N. Cervical length between 14–24 weeks and risk of preterm birth. Am J Obstet Gynecol 1996; 174: S413.
  • 53
    Berghella V, Kuhlman K, Weiner S, Texeira L, Wapner RJ. Cervical funneling: sonographic criteria predictive of preterm delivery. Ultrasound Obstet Gynecol 1997; 10: 161166.
  • 54
    Dowd J, Permezel M, Garland S, de Crespigny L. Is there an interaction between cervical length and cervical microbiology in the pathogenesis of preterm labour? Aust N Z J Obstet Gynaecol 2001; 41: 177181.
  • 55
    Iams JD, Goldenberg RL, Meis PJ. Cervical sonography and risk of preterm birth. Am J Obstet Gynecol 1995; 172: S257.
  • 56
    Goffinet F, Rozenberg P, Kayem G, Perdu M, Philippe HJ, Nisand I. The value of intravaginal ultrasonography of the cervix uteri for evaluation of the risk of premature labor. J Gynecol Obstet Biol Reprod (Paris) 1997; 26: 623629.
  • 57
    Murakawa H, Utumi T, Hasegawa I, Tanaka K, Fuzimori R. Evaluation of threatened preterm delivery by transvaginal ultrasonographic measurement of cervical length. Obstet Gynecol 1993; 82: 829832.
  • 58
    Okitsu O, Mimura T, Nakayama T, Aono T. Early prediction of preterm delivery by transvaginal ultrasonography. Ultrasound Obstet Gynecol 1992; 2: 402409.
  • 59
    Onderoglu LS. Digital examination and transperineal ultrasonographic measurement of cervical length to assess risk of preterm delivery. Int J Gynaecol Obstet 1997; 59: 223228.
  • 60
    Rageth JC, Kernen B, Saurenmann E, Unger C. Premature contractions: possible influence of sonographic measurement of cervical length on clinical management. Ultrasound Obstet Gynecol 1997; 9: 183187.
  • 61
    Rizzo G, Capponi A, Arduini D, Lorido C, Romanini C. The value of fetal fibronectin in cervical and vaginal secretions and of ultrasonographic examination of the uterine cervix in predicting premature delivery for patients with preterm labor and intact membranes. Am J Obstet Gynecol 1996; 175: 11461151.
  • 62
    Vendittelli F, Mamelle N, Munoz F, Janky E. Transvaginal ultrasonography of the uterine cervix in hospitalized women with preterm labor. Int J Gynaecol Obstet 2001; 72: 117125.
  • 63
    Persutte WH, Chyu J, Cioffi-Ragan D, Hobbins JC. Cervical length in twins. Am J Obstet Gynecol 2000; 182: S118.
  • 64
    Benham BN, Balducci J, Atlas RO, Rust OA. Risk factors for preterm delivery in patients demonstrating sonographic evidence of premature dilation of the internal os, prolapse of the membranes in the endocervical canal and shortening of the distal cervical segment by second trimester ultrasound. Aust N Z J Obstet Gynaecol 2002; 42: 4650.
  • 65
    Iams JD, Paraskos J, Landon MB, Teteris JN, Johnson FF. Cervical sonography in preterm labor. Obstet Gynecol 1994; 84: 4046.
  • 66
    Solomon J, Carlson D. Transvaginal ultrasound assessment of cervical length in preterm labor—correlation with digital effacement and pregnancy outcome. Am J Obstet Gynecol 1995; 172: S407.

Supporting Information

  1. Top of page
  2. Abstract
  3. Introduction
  4. Methods
  5. Results
  6. Discussion
  7. Acknowledgements
  8. References
  9. Supporting Information

This article contains supplementary material available via the Internet from the Journal http://www.interscience.wiley.com/jpages/0960-7692/suppmat/index.html

FilenameFormatSizeDescription
suppmat_305.doc54KSupporting Information file suppmat_305.doc

Please note: Wiley Blackwell is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.