First-trimester screening for trisomies 21 and 18.

BACKGROUND: Screening for aneuploid pregnancies is routinely performed after 15 weeks of gestation and has a sensitivity of approximately 65 percent, with a false positive rate of 5 percent. First-trimester markers of aneuploidy have been developed, but their use in combination has not been adequately evaluated in clinical practice. METHODS: We conducted a multicenter study of screening for trisomies 21 and 18 among patients with pregnancies between 74 and 97 days of gestation, based on maternal age, maternal levels of free beta human chorionic gonadotropin and pregnancy-associated plasma protein A, and ultrasonographic measurement of fetal nuchal translucency. A screening result was considered to be positive for trisomy 21 if the calculated risk was at least 1 in 270 pregnancies and positive for trisomy 18 if the risk was at least 1 in 150. RESULTS: Screening was completed in 8514 patients with singleton pregnancies. This approach to screening identified 85.2 percent of the 61 cases of Down's syndrome (95 percent confidence interval, 73.8 to 93.0), with a false positive rate of 9.4 percent (95 percent confidence interval, 8.8 to 10.1). At a false positive rate of 5 percent, the detection rate was 78.7 percent (95 percent confidence interval, 66.3 to 88.1). Screening identified 90.9 percent of the 11 cases of trisomy 18 (95 percent confidence interval, 58.7 to 99.8), with a 2 percent false positive rate. Among women 35 years of age or older, screening identified 89.8 percent of fetuses with trisomy 21, with a false positive rate of 15.2 percent, and 100 percent of fetuses with trisomy 18. CONCLUSIONS: First-trimester screening for trisomies 21 and 18 on the basis of maternal age, maternal levels of free beta human chorionic gonadotropin and pregnancy-associated plasma protein A, and measurement of fetal nuchal translucency has good sensitivity at an acceptable false positive rate.

Late first-trimester placental disruption and subsequent gestational hypertension/preeclampsia.

OBJECTIVE: To evaluate the potential relationship between placental disruption in weeks 13 and 14 and the subsequent development of gestational hypertension or preeclampsia. METHODS: Using subjects recruited during a randomized trial funded by the National Institute of Child Health and Human Development, which compared early amniocentesis and late transabdominal chorionic villus sampling (CVS) in weeks 13 and 14, rates of gestational hypertension and preeclampsia were compared between cases with varying degrees of placental disruption. RESULTS: A total of 3,698 of 3,775 randomized subjects had cytogenetically normal pregnancies and were analyzed. A significantly higher rate of hypertension/preeclampsia was observed in the late CVS group (5.4%, n = 1,878) compared with the early amniocentesis cohort (3.5%, n = 1,820; P = .005). This difference persisted after controlling for maternal age, body mass index, parity, previous preterm delivery, smoking, and fetal gender. Early amniocentesis cases were further stratified on the basis of whether the placenta had been penetrated (n = 460) or not (n = 1,360). Risk of hypertensive complications was lowest if the placenta was not traversed (3.4%), greater with placental penetration (3.9%), and highest when the placenta was directly sampled during CVS (5.4%, P = .02). CONCLUSION: We hypothesize that focal disruption of the placenta at 13-14 weeks may increase the risk of hypertension/preeclampsia. These findings provide support for the theory that disturbances in early placentation lead subsequently to maternal hypertension.

Sequential pathways of testing after first-trimester screening for trisomy 21.

OBJECTIVE: To evaluate the performance and use of second-trimester multiple-marker maternal serum screening for trisomy 21 by women who had previously undergone first-trimester combined screening (nuchal translucency, pregnancy-associated plasma protein A, and free beta-hCG), with disclosure of risk estimates. METHODS: In a multicenter, first-trimester screening study sponsored by the National Institute of Child Health and Human Development, multiple-marker maternal serum screening with alpha-fetoprotein, unconjugated estriol, and total hCG was performed in 4,145 (7 with trisomy 21) of 7,392 (9 with trisomy 21) women who were first-trimester screen-negative and 180 (7 with trisomy 21) of 813 (52 with trisomy 21) who were first-trimester screen-positive. Second-trimester risks were calculated using multiples of the median and a standardized risk algorithm with a cutoff risk of 1:270. RESULTS: Among the first-trimester screen-negative cohort, 6 of 7 (86%) trisomy 21 cases were detected by second-trimester multiple-marker maternal serum screening with a false-positive rate of 8.9%. Among the first-trimester screen-positive cohort, all 7 trisomy 21 cases were also detected in the second trimester, albeit with a 38.7% false-positive rate. CONCLUSION: Our data demonstrate that a sequential screening program that provides patients with first-trimester results and offers the option for early invasive testing or additional serum screening in the second trimester can detect 98% of trisomy 21-affected pregnancies. However, such an approach will result in 17% of patients being considered at risk and, hence, potentially having an invasive test. LEVEL OF EVIDENCE: II-2

Ultrasound and fetal diagnosis.

PURPOSE OF REVIEW: The purpose of this review is to highlight publications from the last year that have advanced the use of ultrasound in obstetrics. RECENT FINDINGS: Anatomic examination of the fetus in the first trimester has been emphasized because it allows for early diagnosis of many conditions. The prevalence of absent nasal bone, a marker for trisomy 21, in euploid fetuses depends on ethnicity. Nasal bone hypoplasia is another marker for Down syndrome. Studies on genetic screening in the first trimester have involved various serum analytes, adjustments in timing and calculations, use in multiple gestations, and the association of extreme measurements with adverse outcomes. A first-trimester integrated screening approach, which incorporates nuchal translucency, nasal bone, crown-rump length, pregnancy-associated plasma protein-A, and free beta-human chorionic gonadotropin, has the potential to maximize detection rates of Down syndrome and trisomy 18 and minimizes the screen-positive rate. The value of combining first and second-trimester results in sequential, contingent, or integrated screening protocols has been assessed. Isolated mild ventriculomegaly (10-12 mm) may prove to be a normal variant, and the role of 'soft' ultrasound markers in genetic counseling continues to be debated. Anomaly or high-risk status detection in the second trimester has been enhanced by the use of Doppler, 3D/4D ultrasound, and magnetic resonance imaging. SUMMARY: Imaging techniques have been critical in the development of screening methods for Down syndrome or trisomy 18 and for euploid fetuses at high risk for adverse outcomes.

Elevated first-trimester nuchal translucency increases the risk of congenital heart defects.

OBJECTIVE: We sought to evaluate the association between first trimester nuchal translucency measurement and the risk for major congenital heart defect in chromosomally normal fetuses. STUDY DESIGN: First trimester (10 weeks 4 days of gestation to 13 weeks 6 days of gestation) nuchal translucency was obtained in a large prospective multicenter National Institute of Child Health and Human Development study for Down syndrome prediction. The study, which was conducted between May 1998 and December 2000, was restricted to singleton pregnancies. Gestational age was determined by crown rump length measurements. Perinatal outcomes were determined and included the frequency of major congenital heart defect, which was defined as those cases that potentially could require surgery, intensive medical therapy, or prolonged follow-up time. Logistic regression analysis was used to determine whether nuchal translucency was a significant predictor of congenital heart defect. RESULTS: There were 8167 chromosomally normal pregnancies, of which 21 cases of major congenital heart defect were identified at follow-up examination (incidence, 2.6/1000 pregnancies). The risk of congenital heart defect rose with increasing nuchal translucency measurements. The mean nuchal translucency value for the normal and congenital heart defect groups were 1.5 mm and 1.9 mm, respectively (P = .05). With a nuchal translucency measurement of < 2.0 mm, the incidence of congenital heart defect was 13 of 6757 pregnancies (1.9 of every 1000 pregnancies). At 2.0 to 2.4 mm, the incidence was 5 of 1032 pregnancies (4.8 of every 1000 pregnancies). At 2.5 to 3.4 mm, the incidence was 2 of 335 pregnancies (6.0 of every 1000 pregnancies). At > or = 3.5 mm, the incidence was 1 of 43 pregnancies (23 of every 1000 pregnancies). Logistic regression analysis confirmed that nuchal translucency was associated significantly with congenital heart defect (odds ratio, 2.1; 95% CI, 1.4-3.1; P = .0004). CONCLUSION: Increased first trimester nuchal translucency measurement was associated with a higher risk of major congenital heart defect in chromosomally normal pregnancies. The practical implications of our findings are that patients with unexplained elevations of nuchal translucency may need referral for a fetal echocardiogram.

Association of extreme first-trimester free human chorionic gonadotropin-beta, pregnancy-associated plasma protein A, and nuchal translucency with intrauterine growth restriction and other adverse pregnancy outcomes.

OBJECTIVE: The purpose of this study was to determine the association between first-trimester trisomy 21 screening markers (free human chorionic gonadotropin-beta [hCG], pregnancy-associated plasma protein A [PAPP-A], and nuchal translucency) and adverse pregnancy outcome. STUDY DESIGN: This was a cohort study of 8012 patients enrolled in a National Institute of Child Health and Human Development-sponsored study of first-trimester trisomy 21 and 18 screening. Trisomy 21 and 18 risk results and individual marker levels in unaffected pregnancies and pregnancies with adverse outcomes were evaluated. RESULTS: PAPP-A <1st percentile (OR 5.4, 95% CI 2.8-10.3) and PAPP-A <5th percentile (OR 2.7, 95% CI 1.9-3.9) and free beta-hCG <1st percentile (OR 2.7, 95% CI 1.3-5.9) were associated with increased risk of intrauterine growth restriction (IUGR) with positive predictive values of 24.1%, 14.1%, and 14.3%, respectively. PAPP-A <5th percentile (OR 2.3 95% CI 1.1-4.7) and nuchal translucency >99th percentile (OR 3.5, 95% CI 1.1-11.3) were associated with increased risk of preterm delivery before 34 weeks. Increased risk at screening for trisomy 21 and 18 identified 16 of the 29 other chromosomal abnormalities (55%). Low free beta-hCG, low PAPP-A, and increased nuchal translucency were all associated with an increased rate of fetal abnormality. CONCLUSION: Extreme values of first-trimester free beta-hCG, PAPP-A, and nuchal translucency are all associated with adverse outcomes. The especially high predictive value for IUGR of PAPP-A levels below the 1st percentile suggests that patients within this group may benefit from increased surveillance for this condition.