Ancillary benefits of prenatal maternal serum screening achieved in the California program

Authors


Abstract

Objective

To evaluate the extent of fetal structural abnormalities, other than neural tube and abdominal wall defects (AWDs), identified by California's Prenatal Screening Program.

Methods

The Quad Marker Prenatal Screening records of 516,172 women were examined for screening interpretation and the diagnosis of structural abnormalities detected via follow-up. Women who were screen-positive for trisomy 21, trisomy 18, neural tube defects (NTDs) or Smith-Lemli-Opitz syndrome (SLOS) received follow-up services at state-approved Prenatal Diagnosis Centers (PDCs). Detailed reports of services and diagnostic information were linked in a database to the original screening results.

Results

A total of 26 323 women received follow-up ultrasound services at the PDCs in the study time period. Of these women, 1085 (4.1%) were identified as having fetuses with significant structural abnormalities, other than NTDs (n = 207) or AWDs (n = 254). In addition to the structural abnormalities, 225 cases of fetal demise, 4 molar pregnancies, 15 cases of twin-to-twin transfusion, and 92 cases with placental abnormalities were identified.

Conclusion

While Prenatal Screening Programs do not explicitly screen for structural abnormalities other than NTDs and AWDs, clearly many other structural abnormalities may be associated with a screen-positive status. Thus, the detection of these additional structural defects can be considered an ancillary program benefit. Copyright © 2010 John Wiley & Sons, Ltd.

INTRODUCTION

The California Prenatal Screening Program works to reduce the occurrence of birth defects and disability by offering prenatal screening and follow-up services to pregnant women in California. The Prenatal Screening Program utilized a Quad Marker Screening Protocol during the study period. In March 2009, a first-trimester screening component was added to the State's Program. The primary focus of Prenatal Maternal Serum Screening Programs has been the detection of Down syndrome, trisomy 18, Smith-Lemli-Opitz syndrome (SLOS), open neural tube defects (NTDs), and abdominal wall defects (AWD) (Kazerouni et al., 2009). Because the California Prenatal Screening Program includes follow-up diagnostic services, the program has been aware that many other structural abnormalities are detected in the screen-positive population. This study is a comprehensive report of abnormalities detected by the second-trimester ultrasound provided to all screen-positive women in the State's Quad Marker Screening Program.

MATERIALS AND METHODS

This study was found to be exempt by the Committee for the Protection of Human Subjects, of the State of California Health and Human Services Agency. The California Expanded Alpha-fetoprotein (AFP) Program is a state-wide prenatal screening program authorized by the State Legislature and implemented by state regulations (California Code of Regulations, 1986). These regulations require that all women seen by prenatal care providers by the 140th day of gestation be provided with a booklet prepared by the department. This booklet describes the Prenatal Birth Defect Screening Program. Prenatal care providers are required to offer the women an opportunity to participate in the program. Follow-up diagnostic services of genetic counseling, ultrasound and amniocentesis are offered at state-approved Prenatal Diagnosis Centers (PDCs) and the costs of these services are covered by the Expanded AFP Program. Details about the California Prenatal Screening Program and its operation were covered in previous publications (Cunningham et al., 1999; Kazerouni et al., 2009).

In July 2007, the California Expanded AFP Screening Program added inhibin as a fourth marker. The program implemented Quad Marker Screening for birth defects, including chromosomal abnormalities, using an automated analytical system (AutoDELFIA, PerkinElmer, Waltham, MA), which measures intact human chorionic gonadotropin (hCG), unconjugated estriol (uE3), and AFP. Dimeric inhibin-A is measured using a Beckman Coulter (Brea, CA) assay system. Women who were screen-positive for trisomy 21, trisomy 18, NTDs or SLOS received follow-up services at state-approved PDCs. Services included genetic counseling, ultrasound, and amniocentesis, if indicated. The structural abnormalities and other ultrasound findings were detected through ultrasound at these second-trimester PDC visits. Detailed reports of services and diagnostic information were submitted on each patient in order for PDCs to obtain reimbursement. These reports were linked in a relational database to the original screening results.

Between 16 July 2007 and 16 January 2009, the Quad Marker Prenatal Screening records of 516,172 women were examined for both the screening interpretation and the structural abnormalities and other ultrasound findings detected via programmatic follow-up services (Figure 1). Additional samples (n = 20 178) were received, but no screening interpretation could be calculated for a variety of reasons. We counted the total number of the specific abnormalities and other ultrasound findings, detected through ultrasound, by karyotype abnormality status if amniocentesis was performed. For these counts, a single fetus could be included in multiple categories.

Figure 1.

The flowchart of women included in the study from July 2007 to January 2009

In addition, a hierarchical classification method was applied to count the number of women with a structural abnormality or other significant ultrasound finding. This method was developed so that a single or twin fetus was counted only once. The hierarchy is as follows: NTD, abdominal wall defect (AWD), fetal demise/molar pregnancy, other structural abnormality, twin-to-twin transfusion, severe oligohydramnios or polyhydramnios, placental disorders and lastly, ultrasound markers. For example, if the ultrasound finding indicated fetal demise and NTD in the fetus of a screened woman, that fetus was counted only once and under the NTD anomaly. Most of the ultrasound markers have been considered as possible markers for aneuploidy and are listed in Table 3 of the results section.

RESULTS

A total of 26 323 (5.1% of all screened women with a screening interpretation), who were screen-positive for trisomy 21, trisomy 18, NTDs or SLOS, received follow-up ultrasound services at state-approved PDCs between 16 July 2007 and 16 January 2009 (Figure 1). The mean age of the study population was 31 years, and the majority (60.1%) of the screen-positive women were Hispanic (Table 1). The census data indicates that among all California Hispanics, 83% are of Mexican descent (United States Census Bureau, 2006–2008). During the study period, 5482 abnormalities, including markers, were detected in 3989 fetuses, representing 1.37 abnormalities per affected fetus. Of these 3989 fetuses with abnormalities, 2985 (74.8%) had a single abnormality, 576 (14.4%) had two abnormalities, and 428 (10.7%) had three or more abnormalities.

Table 1. Demographic characteristics of the 26 323 screen- positivea women
CharacteristicNo. of screened women (%)
  • a

    Screen-positive for Down syndrome, trisomy 18, neural tube defects (NTDs), and Smith-Lemli-Opitz syndrome (SLOS).

  • b

    Mean = 31.0 years; median = 32.0 years.

Maternal age at expected date of deliveryb (y)
Younger than 3516 772 (63.7)
35 and older than 359551 (36.3)
Maternal race or ethnic group
Hispanic15 818 (60.1)
White4695 (17.8)
Asian2495 (9.5)
Black1600 (6.1)
Other1715 (6.5)

Tables 2 and 3 list the total number of specific abnormalities and markers detected through ultrasound. For this analysis, no hierarchy was used, so that a single fetus could be included in multiple categories. Not all women chose to have amniocentesis; for those that did, the count of structural abnormalities separated by karyotype status is listed in Tables 2 and 3. The prevalence of heart and great vessel (23%) and central nervous system (21%) anomalies was the highest among all anomalies. Also, it should be noted that the very high rate of chromosome abnormalities among patients with possible markers for aneuploidy is likely related to their Quad Marker Screen-Positive Status.

Table 2. Number of fetal anomalies by karyotyping status and abnormality among 26 323 screen-positive women from July 2007 to January 2009
  Fetal karyotypeb
   Chromosomal abnormality
AnomalyTotal countaTotalYesNo
  • a

    A single fetus could be counted in multiple categories if more than one anomaly was detected in the fetus.

  • b

    This data only includes karyotypes obtained by amniocentesis at the time of Prenatal Diagnosis Center (PDC) visit.

Central nervous system anomalies
—Acrania8101
—Agenesis of corpus callosum6431
—Anencephaly109514
—Arnold-Chiari malformation6000
—Cerebellar hypoplasia6532
—Dandy-Walker2717710
—Encephalocele201019
—Exencephaly3101
—Holoprosencephaly2617107
—Hydrocephalus NOT with spina bifida—unknown etiology241073
—Myelomeningocele16624
—Rachischisis1000
—Spina bifida3212210
—Spina bifida with hydrocephalus9514
—Ventriculomegaly98593128
—Neural tube defect—unspecified271129
—Other central nervous system76431726
—Total central nervous system anomalies49420687119
Heart and great vessel anomalies
—Abnormal outflow tracts9844
—Atrial septal defect (ASD)2316142
—Cardiomegaly10734
—Coarctation of aorta2220
—Dextrocardia/heart on right side10945
—Endocardial cushion defect/Atrioventricular canal cardiac defect3727234
—Enlarged atrium10826
—Hypoplastic left heart3624186
—Pericardial effusion > 3 mm67462323
—Tetralogy of Fallot11963
—Transposition of the great vessels5413
—Tricuspid regurgitation (TR)5202
—Ventricular septal defect (VSD)1721236558
—Other heart defect105694227
—Total heart and great vessel anomalies502354207147
Digestive system anomalies
—Gastroschisis19256056
—Limb body wall defect13321
—Omphalocele50372116
—Unspecified abdominal wall defect10413
—Ascites/anasarca/edema74412615
—Diaphragmatic hernia131064
—Duodenal obstruction2101
—Absent stomach2519118
—Other abdominal problem4428523
—Total digestive system anomalies42319972127
Urinary tract anomalies
—Absent kidney—unilateral7000
—Absent kidneys—bilateral12422
—Enlarged kidneys8404
—Hydronephrosis107611546
—Multicystic dysplastic kidneys9422
—Renal cysts7312
—Absent bladder5110
—Other kidney/bladder problem3720713
—Total urinary tract anomalies192972869
Musculoskeletal anomalies
—Caudal regression1000
—Skeletal dysplasia2202
—Severe scoliosis10413
—Other skeletal system problem101641846
—Upper extremity—abnormal in position or number of bones10862
—Upper extremity—absent bones4321
—Upper extremity—arthrogryposis multiplex congenita2211
—Upper extremity—clinodactyly13835
—Upper extremity—polydactyly7523
—Lower extremity—unilateral clubfoot3322814
—Lower extremity—bilateral clubfeet57382414
—Lower extremity—abnormal in position or number of bones8211
—Total musculoskeletal anomalies2481586692
Respiratory system anomalies
—Pleural effusion7245369
—Congenital cystic adenomatoid malformation (CCAM)11505
—Total respiratory system anomalies83503614
Miscellaneous
—Cystic hygroma144826715
—Cleft lip3021138
—Cleft palate2000
—Cleft lip and palate211596
—Severe oligohydramnios1191688
—Severe polyhydramnios4101
—Hydrops fetalis66423111
—Intrauterine growth retardation (IUGR)70311120
—Generalized edema2213103
—Multiple congenital anomalies (MCA)11761
—Amniotic band syndrome2000
—Total miscellaneous anomalies49122815573
Placental disorders
—Chorioangioma4000
—Hematoma in placenta11404
—Placental abruption8404
—Placenta previa24505
—Thickened placenta26615
—Other placental problem4216313
—Total placental disorders11535431
Total anomalies25481327655672
Table 3. Number of fetal markers by karyotyping status and abnormality among 26 323 screen-positive women from July 2007 to January 2009
  Fetal karyotypeb
   Chromosomal abnormality
MarkersTotal countaTotalYesNo
  • a

    A single fetus could be counted in multiple categories if more than one anomaly was detected in the fetus.

  • b

    This data only includes karyotypes obtained by amniocentesis at the time of Prenatal Diagnosis Center (PDC) visit.

Banana sign271358
—With neural tube defect (NTD)20945
—Without NTD7413
Lemon sign4225916
—With NTD21945
—Without NTD2116511
Choroid plexus cyst(s)55531479235
Dolichocephaly9202
Mega cisterna magna1000
Echogenic intracardiac foci (EIF)75234564281
Double bubble6422
Echogenic bowel44525447207
Small stomach12413
Dilated stomach6312
Echogenic kidneys16927
Pyelectasis34014836112
Upper extremity—clenched hands4839327
Lower extremity—short femurs1991142589
Nuchal fold (>5 mm)2191326369
Flat nasal bridge3518144
Micrognathia191697
Two-vessel cord (single umbilical artery)189964155
Velamentous insertion9404
Very curled umbilical cord1110
Chorion separation4000
Total markers293415414311110

Of the screen-positive women, who received follow-up ultrasound services at PDCs, 15% (n = 3989) were identified as having an ultrasound marker, structural abnormality or other significant ultrasound finding in their fetus (Table 4). In Table 4, the hierarchical classification method was used so that a single fetus was counted only once. About 5.9% (n = 1546) of these women had fetuses with a structural defect including NTD (n = 207) and AWD (n = 254). In 4.1% (n = 1, 085) of these women with a positive screening test, the structural defect in the fetus (including conjoined and acardiac twins, n = 5), was something other than an NTD or AWD. Women who were screen-positive for more than one disorder had the highest prevalence of structural abnormalities and pregnancy findings. In addition to the structural abnormalities, 229 cases of fetal demise/molar pregnancy, 67 cases of severe oligohydramnios or polyhydramnios, 15 cases of twin-to-twin transfusion, and 92 cases with placental abnormalities were identified. The total number of women identified with fetuses affected by these structural defects and pregnancy findings far exceeds the number of women affected by NTDs (n = 207) and AWDs (n = 254).

Table 4. Number of women with fetal anomalies, markers, and other ultrasonographic findings by screen-positive status and abnormality among 26 323 screen-positive women from July 2007 to January 2009
Screen-positive/ increased risk for selected birth defectsTotal screen-positive with ultrasound servicesTotal ultrasound findingsa (%)NTDAWDFetal demise and molar pregnancyStructural abnormality and conjoined/ acardiac twinsTwin-to-Twin transfusionsSevere oligo/poly hydramniosPlacental disordersMarkers
  • a

    A hierarchical method was developed so that a singleton or twin fetus was counted only once. The hierarchy is as follows: neural tube defect (NTD), abdominal wall defect (AWD), fetal demise/molar pregnancy, other structural abnormality, twin-to-twin transfusion, oligohydramnios/polyhydramnios, placental disorders and lastly, markers.

Singleton pregnancy
SLOS only21246 (22)4271600215
NTD only4160806 (19)1082174015205049190
Trisomy 21 only19 3462403 (12)1176966005271624
Trisomy 18 only1066181 (17)2717800192
SLOS and at least one of: NTD, T21, T18613302 (49)6915879701231
NTD and at least one of: T21, T1820586 (42)93113306717
Trisomy 18 and 2128648 (17)0072000219
Twin pregnancy435117 (27)43729155252
Total26 3233989 (15)20725422910851567922040

The subtraction of 2040 women with an ultrasound finding of a marker from 3989 women having any documented ultrasound finding (Table 4) yields 1949 women who had a pregnancy with a clinically significant ultrasound finding. A total of 72% of these 1949 women had a pregnancy dated by ultrasound prior to referral for follow-up services. The Program has limited information on these prior ultrasounds and cannot be certain that the abnormality had not been detected on the ultrasound performed prior to the PDC visit. The gestational age at the time of these ultrasounds, prior to referral for follow-up services, was the following: 44% less than or equal to 10 weeks, 18% at 11–12 weeks, 21% at 13–15 weeks, and 17% at 16 weeks or more. Given the early gestational age of most of these ultrasounds, it may not have been possible to detect many of these abnormalities at that time.

DISCUSSION

The primary focus of prenatal screening has been the detection of Down syndrome, trisomy 18, open NTDs and AWDs. Because the California Prenatal Screening Program includes follow-up diagnostic services and receives diagnostic outcome reports of these services, the Program has been aware that many other structural abnormalities and pregnancy findings are detected among the screen-positive population. Major fetal abnormalities associated with screen-positive status for SLOS have been previously reported (Craig et al., 2007) as well as increased risk of cardiac defects among fetuses of all screen-positive women (Jelliffe-Pawlowski et al., 2009). Significant associations between several maternal serum markers and an increased risk for multicystic dysplastic kidney, two-vessel cord and hydrocele were demonstrated in participants of the FASTER trial (Hoffman et al., 2008). An increased incidence of structural abnormalities was reported to be associated with elevated mid-trimester levels of hCG (Fejgin et al., 1997). Another study by Celentano et al. (2005) indicated a lack of correlation between elevated maternal serum hCG and fetal congenital anomalies. The current study represents the largest, most comprehensive analysis of the association of screen-positive status and second-trimester ultrasound findings to date.

Follow-up services covered by the California Prenatal Screening Program must occur at state-approved PDCs that meet strict standards. The ultrasound must be performed by a physician who is board certified in radiology or obstetrics/gynecology and has completed a fellowship with subspecialty training related to fetal medicine. All ultrasound practices must be accredited by the American College of Radiology or the American Institute of Ultrasound in Medicine. There are minimum volume requirements for the annual number of prenatal ultrasound exams performed on pregnancies at high risk for fetal abnormalities. The follow-up ultrasound for screen-positive women must meet the American College of Obstetrics and Gynecology, the American Institute of Ultrasound in Medicine and the American College of Radiologists requirements for ultrasound examinations (American College of Radiology, 2007; American Institute of Ultrasound in Medicine, 2007; ACOG Committee on Practice Bulletins, 2009 ). These strict standards might contribute to the level of the prenatal detection of abnormalities in the screen-positive women reported in this study.

The reported prevalence in the general population of fetuses with anomalies at second trimester varies widely from 1.2 to 3.1% (Chitty et al., 1991; Levi et al., 1991; Luck et al., 1992; Shirley et al., 1992; Crane et al., 1994; Levi et al., 1995; Skupski et al., 1996; Boyd et al., 1998; Lee et al., 1998; Magriples et al., 1998; VanDorsten et al., 1998; Bricker et al., 2000). The reported sensitivity for the detection of fetal abnormalities by ultrasound in the second trimester also varies widely from 8.7 to 85.0% (Chitty et al., 1991; Levi et al., 1991; Luck et al., 1992; Shirley et al., 1992; Crane et al., 1994; Levi et al., 1995; Skupski et al., 1996; Boyd et al., 1998; Lee et al., 1998; Magriples et al., 1998; VanDorsten et al., 1998; Bricker et al., 2000). Of the screen-positive group of women in our study, 5.9% of the women had a fetus with a structural defect. After exclusion of NTDs and AWDs, which are known to be enriched in this population, the rate of structural abnormalities is still 4.1%. This rate among the screen-positive women exceeds the highest reported background rates, even if 100% detection is assumed.

Antenatal diagnosis of major fetal abnormalities offers a variety of options for the pregnant women, including choosing to deliver at a center equipped to perform the appropriate neonatal surgical procedures, psychological preparation for the birth of a child with abnormalities or termination of the pregnancy. The median gestational age that the PDC ultrasound was performed is 19 weeks 0 days. As there is considerable variation in the protocols regarding ultrasounds performed among prenatal care providers in California, it is unclear how many of these abnormalities would have been detected at a later ultrasound during the pregnancy. A high percentage (72%) of the women had a previous ultrasound, but many were at an earlier gestational age where fewer abnormalities would be expected to be detected.

While the information presented on ultrasound findings in screen-positive women should be of use to prenatal care providers and genetic counselors in explaining the benefits of prenatal screening and the possible significance of a screen-positive status to patients, this study has several limitations. The data only includes ultrasound findings and chromosomal abnormalities detected at the PDC visits. It does not include any data on structural or chromosomal abnormalities detected only at birth. In addition, the study does not include any information on the 10.3% of screen-positive women who do not receive follow-up services via the Expanded AFP Program. A significant portion of these women may have declined services because an abnormality or demise had already been detected. Furthermore, the results of this study, like those from all studies of screen-positive populations, depend on the particular choice of cut-offs for screen-positive status and the resulting rate of referrals to the PDCs.

While maternal serum prenatal screening tests do not explicitly screen for structural abnormalities other than NTDs and AWDs, clearly many other structural abnormalities and pregnancy findings may be associated with a screen-positive status. The total number of women identified with fetuses affected with structural defects (n = 1085) far exceeds the number of women identified with fetuses affected by NTDs (n = 207) and AWD (n = 254). Thus, the identification of these additional structural defects can be considered an ancillary benefit to the State of California's Prenatal Screening Program.

Acknowledgements

We thank the Genetic Disease Laboratory Branch for the laboratory analysis of the screening specimens, as well as the Prenatal Screening Branch and Program Standards and Quality Assurance Branch for the implementation of the screening program. We also thank the Prenatal Diagnostic Centers for providing the data on ultrasound findings among screen-positive women in the Program. This study was supported by funding from the Genetic Disease Screening Program, California Department of Public Health.

Ancillary