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Keywords:

  • embryo;
  • gestational sac;
  • intrauterine pregnancy of uncertain viability;
  • IPUV;
  • miscarriage;
  • ultrasound

Abstract

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

Objectives

There is significant variation in cut-off values for mean gestational sac diameter (MSD) and embryo crown–rump length (CRL) used to define miscarriage, values suggested in the literature ranging from 13 to 25 mm for MSD and from 3 to 8 mm for CRL. We aimed to define the false-positive rate (FPR) for the diagnosis of miscarriage associated with different CRL and MSD measurements with or without a yolk sac in a large study population of patients attending early pregnancy clinics. We also aimed to define cut-off values for CRL and MSD that, on the basis of a single measurement, can definitively diagnose a miscarriage and so exclude possible inadvertent termination of pregnancy.

Methods

This was an observational cross-sectional study. Data were collected prospectively according to a predefined protocol. Intrauterine pregnancy of uncertain viability (IPUV) was defined as an empty gestational sac or sac with a yolk sac but no embryo seen with MSD < 20 or < 30 mm or an embryo with an absent heartbeat and CRL < 6 mm or < 8 mm. We recruited to the study 1060 consecutive women with IPUV. The endpoint was presence or absence of a viable pregnancy at the time of first-trimester screening ultrasonography between 11 and 14 weeks. The sensitivity, specificity, positive and negative predictive values were calculated for potential cut-off values to define miscarriage from MSD 8 to 30 mm with or without a yolk sac and from CRL 3 to 8 mm.

Results

Of the 1060 women with a diagnosis of IPUV, 473 remained viable and 587 were non-viable by the time of the 11–14-week scan. In the absence of both embryo and yolk sac, the FPR for miscarriage was 4.4% when an MSD cut-off of 16 mm was used and 0.5% for a cut-off of 20 mm. There were no false-positive test results for miscarriage when a cut-off of MSD ≥ 21 mm was used. If a yolk sac was present but an embryo was not, the FPR for miscarriage was 2.6% for an MSD cut-off of 16 mm and 0.4% for a cut-off of 20 mm, with no false-positive results when a cut-off of MSD ≥ 21 mm was used. When an embryo was visible with an absent heartbeat, using a CRL cut-off of 4 mm the FPR for miscarriage was 8.3%, and for a CRL cut-off of 5 mm it was also 8.3%. There were no false-positive results using a CRL cut-off of ≥ 5.3 mm.

Conclusions

These data show that some current definitions used to diagnose miscarriage are potentially unsafe. Current national guidelines should be reviewed to avoid inadvertent termination of wanted pregnancies. An MSD cut-off of > 25 mm and a CRL cut-off of > 7 mm could be introduced to minimize the risk of a false-positive diagnosis of miscarriage. Copyright © 2011 ISUOG. Published by John Wiley & Sons, Ltd.


Introduction

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

The current criteria used to diagnose miscarriage vary. For example, in the UK an empty gestational sac, visualized using transvaginal ultrasound, with a mean gestational sac diameter (MSD) of ≥ 20 mm may be classified as a miscarriage according to the Royal College of Obstetricians and Gynaecologists' (RCOG) guideline for the management of early pregnancy loss1. An empty gestational sac of < 20 mm is defined as an intrauterine pregnancy of uncertain viability (IPUV) and in order to confirm or refute viability, a repeat scan at a minimal interval of 1 week is advised. This guidance, though not explicit, implies that an empty gestational sac of > 20 mm may be classified as a miscarriage. No comment is given regarding criteria that should be used at any repeat scan to define miscarriage. The same guideline suggests an embryo with a crown–rump length (CRL) ≥ 6 mm and no fetal heartbeat may also be classified as a miscarriage. This guidance is classed as Grade IV, which is defined by the RCOG as being ‘obtained from expert committee reports or opinions and/or clinical experience of respected authorities’ and so is not evidence-based. Following a previous public enquiry in the UK, cut-off values for MSD of 20 mm and for CRL of 10 mm were proposed, but never on the basis of a single scan and only after a repeat scan had been carried out at least 7 days later2. In contrast, the American College of Radiology (ACR) guidelines define a miscarriage on the basis of an empty gestational sac with a MSD ≥ 16 mm or, if present, an embryo with a CRL measuring ≥ 5 mm and no heartbeat. This guidance is based on two small studies from the late 1980s3, 4. Other studies have concluded that an empty gestational sac with a MSD of ≥ 25 mm or a MSD of ≥ 20 mm with a yolk sac present can be used as a safe approach to diagnose miscarriage5. A CRL cut-off value of ≥ 4 mm with no cardiac activity has also been suggested6. A review article has proposed a CRL cut-off of ≥ 5 mm and an appropriate cut-off value for MSD of ≥ 13 mm with or without a yolk sac7. Against this background, it is concerning that Elson et al.8 reported two pregnancies with empty gestational sacs measuring 18 and 20 mm that were found to be viable after further follow-up. The authors point out that: ‘ultrasound is an operator-dependent method and it is conceivable that an inexperienced operator may fail to detect an embryo in a relatively large sac due to a poor examination technique’.

In the study by Pexsters et al. in this issue of the Journal9, there was clinically significant interobserver variation in MSD measurements taken by two experienced examiners. The implications of this finding for the use of cut-off values for MSD to define miscarriage are important. Great care must be taken around whatever decision boundary is used if a mistake is not to be made.

The variation both in the literature and in national guidelines, regarding the definitions used to make such a fundamental decision as the viability of a human embryo, is concerning, especially as any error may be associated with inadvertent termination of pregnancy. In this multicenter observational study, we aimed to establish the false-positive rate (FPR) for miscarriage for different cut-off values of MSD with and without a yolk sac and CRL. We further aimed to define cut-off values for both MSD and CRL that can be used confidently to classify a pregnancy as non-viable.

Patients and Methods

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

This was a multicenter observational study. Data were collected prospectively from three London hospitals within the Imperial group between September 2010 and March 2011. Additionally, recruitment at St George's took place prospectively between January and October 2006 as part of a study to develop scoring systems to predict miscarriage10. For Queen Charlottes and Chelsea Hospital, of 406 women initially recruited nine were excluded as measurements of MSD and CRL were missing, leaving 397 in the analysis. For St George's Hospital, of 540 initially recruited 80 were excluded as viability data were missing and one case was excluded due to there being no MSD available, leaving 459 in the analysis. For Chelsea and Westminster Hospital, 22 of 108 women were excluded for absent viability data or missing MSD measurements, leaving 86 cases. None of the 118 cases from St Mary's Hospital was excluded. In total, 1060 eligible women were recruited into the study. The breakdown of cases from each unit are shown in Table 1.

Table 1. Data overview for women with intrauterine pregnancy of uncertain viability from four London teaching hospitals included in the study
Hospital/ParameternViable pregnancy (n (%))Non-viable pregnancy (n (%))
  1. CRL, embryo crown–rump length; MSD, mean gestational sac diameter; YS, yolk sac.

Queen Charlottes and Chelsea Hospital   
 MSD, no YS, no CRL14045 (32.1)95 (67.9)
 MSD, YS, no CRL16586 (52.1)79 (47.9)
 CRL9215 (16.3)77 (83.7)
St Mary's Hospital   
 MSD, no YS, no CRL3313 (39.4)20 (60.6)
 MSD, YS, no CRL6348 (76.2)15 (23.8)
 CRL223 (13.6)19 (86.4)
St George's Hospital   
 MSD, no YS, no CRL267117 (43.8)150 (56.2)
 MSD, YS, no CRL156104 (66.7)52 (33.3)
 CRL362 (5.6)34 (94.4)
Chelsea and Westminster Hospital   
 MSD, no YS, no CRL228 (36.4)14 (63.6)
 MSD, YS, no CRL3528 (80)7 (20)
 CRL294 (13.8)25 (86.2)
All centers   
 MSD, no YS, no CRL462183 (39.6)279 (60.4)
 MSD, YS, no CRL419266 (63.5)153 (36.5)
 CRL17924 (13.4)155 (86.6)
Total1060473 (44.6)587 (55.4)

Indications for ultrasonography included lower abdominal pain, vaginal bleeding, poor obstetric history and estimation of gestational age. Women classified with IPUV were eligible for inclusion unless they were clinically unstable or subsequently underwent termination of pregnancy. In three hospitals, IPUV was defined using transvaginal ultrasound according to the RCOG Green-Top guidelines1 as an intrauterine sac of < 20 mm MSD with no obvious yolk sac or embryo, or an embryo with a CRL of < 6 mm with no fetal heart activity. At Queen Charlottes and Chelsea Hospital, the definition of IPUV was extended to include an intrauterine sac of < 30 mm MSD or an embryo of CRL < 8 mm. The cut-off values used reflected the clinical practice in the four units; however, the higher values used at Queen Charlottes and Chelsea Hospital enabled assessment of the performance of cut-off values greater than those most widely used. In order to establish immediate viability, scans were repeated 7–14 days later. The final outcome of the study was viability of the pregnancy at 11–14 weeks, at the time of the routine nuchal translucency scan.

All women underwent sonographic assessment with a Voluson E8 (GE Medical Systems, Zipf, Austria), Aloka SSD 5000 (Aloka, Tokyo, Japan) or Samsung Medison Accuvix XG (Samsung Medison, Seoul, Korea) ultrasound machine, equipped with a 6–12-MHz transvaginal transducer for B-mode imaging. All examinations were performed by gynecologists or nurses with training and experience relating to the use of ultrasound in early pregnancy and were performed in dedicated early pregnancy assessment units. Standardized assessments of sonographic variables included: measurement of CRL in the sagittal plane; measurement of sac diameter in three orthogonal planes i.e. MSD; determination of presence of a yolk sac; and detection of embryonic cardiac activity. Demographic variables recorded included date of last menstrual period or known date of conception after infertility treatment, the woman's age and gestational age at presentation. Symptoms recorded included vaginal bleeding with or without clots and pain.

The study was registered as an audit of the performance of cut-off values used to diagnose miscarriage. For a defined subset of patients recruited at St George's Hospital, ethical committee approval was obtained in January 200610.

Statistical analysis

For the four centers separately as well as for the combined set, we calculated the sensitivity, specificity and positive and negative predictive values for MSD with or without yolk sac from 8 to 30 mm, and for CRL from 3 to 8 mm. For each cut-off value, the 95% confidence interval for specificity of detection of viable pregnancies was calculated with the Wilson score method11. Analyses were performed in Matlab R2010b for Mac (MathWorks, Matrix House, Cambridge, UK).

Results

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

Among the 1060 included women with a diagnosis of IPUV at initial scan, 473 (44.6%) cases remained viable at the 11–14-week scan and 587 (55.4%) cases were non-viable by this time (Table 1). When the yolk sac and embryo were not visualized on ultrasound, the use of an MSD cut-off of 16 mm to diagnose miscarriage was associated with a FPR (viable pregnancy) of 4.4%. This FPR fell to 0.5% with an MSD cut-off of 20 mm. There were no misdiagnosed cases when an MSD cut-off of ≥ 21 mm was used (Table 2). When the yolk sac was visualized but an embryo was not, the FPR was 2.6% for an MSD cut-off of 16 mm and it was 0.4% for a cut-off of 20 mm, with no false-positive cases when the MSD was ≥ 21 mm (Table 3). When an embryo was visible with absent heartbeat, the FPR for miscarriage was 8.3% using a CRL cut-off of 4 mm and using a CRL cut-off of 5 mm. There were no false-positive results for a CRL ≥ 5.3 mm (Table 4). FPRs and optimal cut-off values were similar for the four units individually (Tables S1–S12).

Table 2. Performance in all centers of different cut-off values of mean gestational sac diameter (MSD) in absence of both yolk sac and embryo for prediction of non-viable pregnancy at 11–14 weeks (n = 462)
MSD (mm)Sensitivity (% (n))Specificity (% (n))95% CI for specificityPPVNPV
  1. NPV, negative predictive value; PPV, positive predictive value.

849.1 (137/279)63.9 (117/183)56.8–70.50.670.45
1035.8 (100/279)80.3 (147/183)74.0–85.40.740.45
1226.5 (74/279)88.0 (161/183)82.5–91.90.770.44
1417.6 (49/279)92.9 (170/183)88.2–95.80.790.43
1613.6 (38/279)95.6 (175/183)91.6–97.80.830.42
186.5 (18/279)98.9 (181/183)96.1–99.70.900.41
202.9 (8/279)99.5 (182/183)97.0–99.90.890.40
212.9 (8/279)100 (183/183)97.9–10010.40
Table 3. Performance in all centers of different cut-off values of mean gestational sac diameter (MSD) in presence of yolk sac but absence of embryo for prediction of non-viable pregnancy at 11–14 weeks (n = 419)
MSD (mm)Sensitivity (% (n))Specificity (% (n))95% CI for specificityPPVNPV
  1. NPV, negative predictive value; PPV, positive predictive value.

869.9 (107/153)35.7 (95/266)30.2–41.60.380.67
1047.7 (73/153)59.8 (159/266)53.8–65.50.410.67
1236.6 (56/153)77.8 (207/266)72.5–82.40.490.68
1427.5 (42/153)91.7 (244/266)87.8–94.50.660.69
1620.9 (32/153)97.4 (259/266)94.7–98.70.820.68
1813.7 (21/153)98.1 (261/266)95.7–99.20.810.66
209.8 (15/153)99.6 (265/266)97.9–99.90.940.66
219.2 (14/153)100 (266/266)98.6–10010.66
Table 4. Performance in all centers of different cut-off values of crown–rump length (CRL) in absence of fetal heart activity for prediction of non-viable pregnancy at 11–14 weeks (n = 179)
CRL (mm)Sensitivity (% (n))Specificity (% (n))95% CI for specificityPPVNPV
  1. NPV, negative predictive value; PPV, positive predictive value.

3.071.6 (111/155)75.0 (18/24)55.1–88.00.950.29
3.267.1 (104/155)83.3 (20/24)64.2–93.30.960.28
3.463.9 (99/155)87.5 (21/24)69.0–95.70.970.27
3.661.9 (96/155)87.5 (21/24)69.0–95.70.970.26
3.856.8 (88/155)87.5 (21/24)69.0–95.70.970.24
4.049.7 (77/155)91.7 (22/24)74.2–97.70.970.22
4.241.9 (65/155)91.7 (22/24)74.2–97.70.970.20
4.437.4 (58/155)91.7 (22/24)74.2–97.70.970.18
4.634.2 (53/155)91.7 (22/24)74.2–97.70.960.18
4.829.7 (46/155)91.7 (22/24)74.2–97.70.960.17
5.022.6 (35/155)91.7 (22/24)74.2–97.70.950.15
5.220.0 (31/155)91.7 (22/24)74.2–97.70.940.15
5.316.8 (26/155)100 (24/24)86.2–10010.16

If a cut-off of 16 mm for MSD had been used for those 462 women with an empty gestational sac, 38 of 279 (13.6%) miscarriages would have been foreseen at the first scan, whilst eight of 183 (4.4%) viable pregnancies would have been terminated if these women with IPUV had gone forward to surgical or medical evacuation of the pregnancy. When a yolk sac was visible, 32 of 153 (20.9%) miscarriages and seven of 266 (2.6%) viable pregnancies had an MSD of ≥ 16 mm.

Discussion

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

To our knowledge this is the largest study that has been carried out to assess the criteria currently used to define miscarriage. Our data support those of a previous retrospective case review study by Rowling et al. in Radiology12, in which five (8%) of 59 patients with no embryo visible and with an MSD of ≥ 16 mm were subsequently observed to develop live embryos.

A strength of our study is that the data were collected prospectively according to a defined protocol. Furthermore, the study took place in four different early pregnancy units with different patient populations, so the results are unlikely to be a reflection of an individual unit's or clinician's practice and so are likely to be generally applicable. In this context, it is notable that the optimal cut-off values and FPR for miscarriage was similar in all four units. In addition, the ultrasound scans were all carried out using high-quality equipment, and by practitioners with an interest in the diagnosis and management of early pregnancy complications. It is therefore likely that the quality of any ultrasound examination performed was relatively good. The results therefore may reflect the ‘best case’ scenario, with more false-positive results for miscarriage occurring with less experienced operators or with poor equipment. Using viability at 11–14 weeks as the primary outcome measure is also more clinically useful, as around 14% of first-trimester pregnancies with visualized cardiac activity subsequently miscarry13, while the miscarriage rate after 12 weeks is very much lower and has been reported to be as low as 0.5%14. This has allowed us to demonstrate that empty sacs with an MSD equal to or greater than those currently used to define miscarriage may remain viable and are not a definitive marker of impending pregnancy failure. It does not seem likely that the different cut-off values for MSD and CRL used to define IPUV in our study centers will have affected the results as there were no viable pregnancies observed above the minimum thresholds of 20 mm for MSD or 6 mm for CRL. A weakness of the study is that, despite the large number of cases included, there were still a relatively small number of cases at or around the critical decision boundaries used to define miscarriage.

Unpublished data of a recent survey conducted by the association of early pregnancy units in the UK illustrates the potential size of the problem (Kirk et al., unpubl. data). This survey suggested that at least 500 000 women attend such units each year. The prevalence of IPUV with an empty gestational sac of < 20 mm in a recent publication of all women attending such an early pregnancy unit was 16%10. If we apply a cut-off of 16 mm for MSD in the absence of a yolk sac to define miscarriage, this could lead to 3520 viable pregnancies in the UK each year being classified as a miscarriage and potentially undergoing termination. To put this number in context, there are approximately 4000 stillbirths reported in the UK annually15. Applying a cut-off for MSD of 20 mm could lead to 400 viable pregnancies potentially being misclassified, compared with approximately 300 ‘cot deaths’ reported in the UK each year16. These numbers are significant and relate to pregnancies that would be highly likely to reach term14. The use of expectant management or non-intervention to manage miscarriage may counterbalance the risk of misdiagnosis in some cases, but does not detract from the need for definitive clear guidance.

A study in this issue of the Journal, reporting the inter- and intraobserver variability of MSD and CRL measurements reveals, for MSD, the limits of agreement to be ± 18.78%9. So, an MSD measurement of 20 mm by one examiner may translate to a measurement of anywhere between 16.8 and 24.5 mm for a second examiner, while a CRL measurement of 6 mm translates to a range for a second examiner of between 5.4 mm and 6.7 mm. This suggests that safe cut-off values to define miscarriage may have to be significantly increased to exclude any errors. These data suggest that decisions to intervene and allow the potential termination of a viable pregnancy are being taken based on inappropriate guidance.

In many developed countries, women can now be managed expectantly without the need for medical treatment or surgery. Waiting 7–10 days in order to repeat a scan is highly unlikely to lead to physical harm. The anxiety associated with being uncertain about the status of a pregnancy is very significant, but should be balanced against the possibility of inadvertent termination which is surely the worst possible outcome for any woman.

Taking inter- and intraobserver variation of measurements into account, an empty MSD cut-off of 25 mm, an MSD cut-off with a yolk sac present of 25 mm and a CRL cut-off of 7.0 mm could be introduced and, based on the available evidence, would be associated with a minimal risk of a false-positive diagnosis of miscarriage. Emphasis should be placed on the need to repeat scans when measurements are around the decision boundaries. There should be clarity regarding what might be expected on a repeat scan. In a further paper in this Journal17, we have shown that it is possible for there to be no growth in MSD over at least 10 days and the pregnancy still to be viable. We found no viable pregnancies when a repeat scan found that the gestational sac was still empty with no yolk sac or embryo present. As current guidance is based on such limited evidence, these changes in approach would seem prudent pending the publication of larger prospective studies containing greater numbers of patients around the decision boundaries. The data in this report and others suggest that national guidelines should be reviewed or applied with caution if pregnant women are to be confident that when they are informed that they have suffered a miscarriage, there is no chance of an error.

SUPPORTING INFORMATION ON THE INTERNET

The following supporting information may be found in the online version of this article:

equation imageTable S1 Queen Charlottes and Chelsea Hospital: performance of different cut-off values of mean gestational sac diameter (MSD) in absence of both yolk sac and embryo for prediction of non-viable pregnancy at 11–14 weeks (n = 140).

Table S2 Queen Charlottes and Chelsea Hospital: performance of different cut-off values of mean gestational sac diameter (MSD) in presence of yolk sac but absence of embryo for prediction of non-viable pregnancy at 11–14 weeks (n = 165).

Table S3 Queen Charlottes and Chelsea Hospital: performance of different cut-off values of crown–rump length (CRL) in absence of fetal heart activity for prediction of non-viable pregnancy at 11–14 weeks (n = 92).

Table S4 St Mary's Hospital: performance of different cut-off values of mean gestational sac diameter (MSD) in absence of both yolk sac and embryo for prediction of non-viable pregnancy at 11–14 weeks (n = 33).

Table S5 St Mary's Hospital: performance of different cut-off values of mean gestational sac diameter (MSD) in presence of yolk sac but absence of embryo for prediction of non-viable pregnancy at 11–14 weeks (n = 63).

Table S6 St Mary's Hospital: performance of different cut-off values of crown–rump length (CRL) in absence of fetal heart activity for prediction of non-viable pregnancy at 11–14 weeks (n = 22).

Table S7 St George's Hospital: performance of different cut-off values of mean gestational sac diameter (MSD) in absence of both yolk sac and embryo for prediction of non-viable pregnancy at 11–14 weeks (n = 267).

Table S8 St George's Hospital: performance of different cut-off values of mean gestational sac diameter (MSD) in presence of yolk sac but absence of embryo for prediction of non-viable pregnancy at 11–14 weeks (n = 156).

Table S9 St George's Hospital: performance of different cut-off values of crown–rump length (CRL) in absence of fetal heart activity for prediction of non-viable pregnancy at 11–14 weeks (n = 36).

Table S10 Chelsea and Westminster Hospital: performance of different cut-off values of mean gestational sac diameter (MSD) in absence of both yolk sac and embryo for prediction of non-viable pregnancy at 11–14 weeks (n = 22).

Table S11 Chelsea and Westminster Hospital: performance of different cut-off values of mean gestational sac diameter (MSD) in presence of yolk sac but absence of embryo for prediction of non-viable pregnancy at 11–14 weeks (n = 35).

Table S12 Chelsea and Westminster Hospital: performance of different cut-off values of crown–rump length (CRL) in absence of fetal heart activity for prediction of non-viable pregnancy at 11–14 weeks (n = 29).

Acknowledgements

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

T.B. is supported by the Imperial Healthcare NHS Trust NIHR Biomedical Research Centre.

REFERENCES

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

Supporting Information

  1. Top of page
  2. Abstract
  3. Introduction
  4. Patients and Methods
  5. Results
  6. Discussion
  7. Acknowledgements
  8. REFERENCES
  9. Supporting Information
FilenameFormatSizeDescription
uog_10109_sm_supportinginfo_tabs1.doc36KSupporting Information: Table S1 Queen Charlottes and Chelsea Hospital: performance of different cut-off values of mean gestational sac diameter (MSD) in absence of both yolk sac and embryo for prediction of non-viable pregnancy at 11–14 weeks (n = 140).
uog_10109_sm_supportinginfo_tabs2.doc35KSupporting Information: Table S2 Queen Charlottes and Chelsea Hospital: performance of different cut-off values of mean gestational sac diameter (MSD) in presence of yolk sac but absence of embryo for prediction of non-viable pregnancy at 11–14 weeks (n = 165).
uog_10109_sm_supportinginfo_tabs3.doc35KSupporting Information: Table S3 Queen Charlottes and Chelsea Hospital: performance of different cut-off values of crown–rump length (CRL) in absence of fetal heart activity for prediction of non-viable pregnancy at 11–14 weeks (n = 92).
uog_10109_sm_supportinginfo_tabs4.doc34KSupporting Information: Table S4 St Mary's Hospital: performance of different cut-off values of mean gestational sac diameter (MSD) in absence of both yolk sac and embryo for prediction of non-viable pregnancy at 11–14 weeks (n = 33).
uog_10109_sm_supportinginfo_tabs5.doc35KSupporting Information: Table S5 St Mary's Hospital: performance of different cut-off values of mean gestational sac diameter (MSD) in presence of yolk sac but absence of embryo for prediction of non-viable pregnancy at 11–14 weeks (n = 63).
uog_10109_sm_supportinginfo_tabs6.doc38KSupporting Information: Table S6 St Mary's Hospital: performance of different cut-off values of crown–rump length (CRL) in absence of fetal heart activity for prediction of non-viable pregnancy at 11–14 weeks (n = 22).
uog_10109_sm_supportinginfo_tabs7.doc35KSupporting Information: Table S7 St George's Hospital: performance of different cut-off values of mean gestational sac diameter (MSD) in absence of both yolk sac and embryo for prediction of non-viable pregnancy at 11–14 weeks (n = 267).
uog_10109_sm_supportinginfo_tabs8.doc35KSupporting Information: Table S8 St George's Hospital: performance of different cut-off values of mean gestational sac diameter (MSD) in presence of yolk sac but absence of embryo for prediction of non-viable pregnancy at 11–14 weeks (n = 156).
uog_10109_sm_supportinginfo_tabs9.doc32KSupporting Information: Table S9 St George's Hospital: performance of different cut-off values of crown–rump length (CRL) in absence of fetal heart activity for prediction of non-viable pregnancy at 11–14 weeks (n = 36).
uog_10109_sm_supportinginfo_tabs10.doc32KSupporting Information: Table S10 Chelsea and Westminster Hospital: performance of different cut-off values of mean gestational sac diameter (MSD) in absence of both yolk sac and embryo for prediction of non-viable pregnancy at 11–14 weeks (n = 22).
uog_10109_sm_supportinginfo_tabs11.doc35KSupporting Information: Table S11 Chelsea and Westminster Hospital: performance of different cut-off values of mean gestational sac diameter (MSD) in presence of yolk sac but absence of embryo for prediction of non-viable pregnancy at 11–14 weeks (n = 35).
uog_10109_sm_supportinginfo_tabs12.doc33KSupporting Information: Table S12 Chelsea and Westminster Hospital: performance of different cut-off values of crown–rump length (CRL) in absence of fetal heart activity for prediction of non-viable pregnancy at 11–14 weeks (n = 29).

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