Practitioner–Specific Medians for Nuchal Translucency to Improve First-Trimester Screening Performance:

First-Trimester Abdominal Circumference (Versus Crown Rump Length) Improves Precision in Inter- and Intraobserver Variability

OBJECTIVES

The aim of this study was to evaluate inter- and intraobserver variability of first-trimester biometric measurements and crown-rump length (CRL) and to compare the accuracy and precision of CRL with these biometric measurements used in the interpretation of first-trimester nuchal translucency (NT).

METHODS

Women presenting for a first trimester ultrasound were recruited. Both a sonographer, and a maternal fetal medicine specialist individually examined each participant. Each examiner obtained three independent measurements of CRL, a standardized set of biometric measurements (biparietal diameter, occipitofrontal diameter, head circumference, abdominal circumference, humerus length, and femur length), and an NT between 11 0/7 and 13 6/7 weeks of gestation. Biometry-specific expected NT values were calculated using linear and quadratic regression models and were used to convert results into multiples of the median.

RESULTS

Fetal biometric measurements, CRL, and NT measurements were obtained in 356 consecutive pregnancies with singleton fetuses. CRL demonstrated the least intra- and interobserver variability as demonstrated by the smallest coefficient of variance. However, abdominal circumference and head circumference were not statistically different from CRL variance. CRL and abdominal circumference showed the smallest standard deviation when calculating multiples of the median for NT interpretation.

CONCLUSION

First-trimester abdominal circumference demonstrates the most intra- and interobserver precision for dating and calculating NT multiples of the median, which could potentially be useful with obesity and in any setting with technical limitations of sonography.

Detection Rates for Aneuploidy by First-Trimester and Sequential Screening

OBJECTIVE

To estimate detection rates for aneuploidy by first-trimester and sequential screening.

METHODS

The study included women with singleton pregnancies who participated in the California Prenatal Screening Program with estimated delivery dates from August 2009 to December 2012 who had first- or first- and second-trimester (sequential) screening. Detection rates were measured for target (trisomies 21 and 18) and other aneuploidies identified from the California Chromosome Defect Registry.

RESULTS

Of 452,901 women screened, 17,435 (3.8%) were screen-positive for Down syndrome only; 433 (0.1%) for trisomy 18 only; 1,689 (0.4%) for both Down syndrome and trisomy 18; and 2,947 (0.7%) for neural tube defects, Smith-Lemli-Opitz syndrome, or for multiple conditions. The detection rates were Down syndrome-92.9% (95% confidence interval [CI] 91.4-94.2); trisomy 18-93.2% (95% CI 90.5-95.9); trisomy 13-80.4% (95% CI 73.9-86.9); 45,X-80.1% (95% CI 73.9-86.3), and triploidy-91.0% (95% CI 84.2-97.9). Overall, the detection rate for chromosome abnormalities was 81.6% (95% CI 80.0-83.1) at an overall false-positive rate of 4.5%.

CONCLUSION

First-trimester and sequential screening are sensitive and specific for the broad range of karyotype abnormalities seen in the population.

LEVEL OF EVIDENCE

II.

Outcomes of pregnancies with more than one positive prenatal screening result in the first or second trimester

OBJECTIVE

To describe adverse outcomes and fetal abnormalities in women with a positive prenatal screening result for more than one disorder.

STUDY DESIGN

Study participants were drawn from a population of 452 901 women pregnant with singletons entering the California Prenatal Screening Program in their first-trimester. Risk assessment was provided for trisomy 21 and trisomy 18 in the first-trimester and trisomy 21, trisomy 18, neural tube defects, and Smith-Lemli-Opitz syndrome in the second-trimester. Inclusion in this study required positive screening for more than one of the screened conditions and a completed outcome of pregnancy survey.

RESULTS

A total of 874 women met our study inclusion criteria. Over 25% of these pregnancies had a fetus with a chromosomal abnormality. Of the euploid pregnancies, 6.9% had a fetus with a major birth defect. Of the pregnancies with a fetus with neither a chromosomal abnormality nor a major birth defect, 9.3% ended in fetal demise. Overall, more than 50% of women with multiple positive screening results had either a fetus with a birth defect or a poor pregnancy outcome.

CONCLUSION

Although it is rare to screen positive for more than one condition, such results indicate a very high risk for chromosomal abnormality, fetal demise, or structural abnormality.

Risk of critical congenital heart defects by nuchal translucency norms

OBJECTIVE

The purpose of this study was to compare the performance of first-trimester nuchal translucency (NT) cutoff of ≥3.5 mm with NT percentiles that were calculated for crown-rump length to identify fetuses with critical congenital heart defects (CCHDs).

STUDY DESIGN

This was a population-level study of singleton pregnancies in California with NT measurements performed between 11 and 14 weeks of gestation. Eligible cases were those that resulted in live births from 2009-2010 and had information about the presence or absence of CCHDs available in the hospital discharge records through age 1 year (n = 76,089). Logistic binomial regression methods were used to compare the rate of CCHDs by an NT percentile for crown-rump length and millimeter cutpoints.

RESULTS

Compared with fetuses with an NT measurement of <90th percentile, fetuses with an NT of ≥99th percentile were >5 times as likely to have a CCHD (1.3% vs 0.2%; relative risk, 5.66; 95% confidence interval, 3.19-10.04) and fetuses with an NT measurement ≥3.5 mm were >12 times as likely to have a CCHD (2.8% vs 0.2%; relative risk, 12.28; 95% confidence interval, 5.11-29.51). NT ≥99th percentile had a sensitivity of 5.8% and a specificity of 98.9% for the detection of CCHDs compared with 2.6% and 99.8% for NT ≥3.5 mm.

CONCLUSION

Results show that NT measurements of ≥99th percentile and ≥3.5 mm are not equivalent and that substantial risk for CCHD extends to the less restrictive ≥99th percentile cutpoint. Data suggest that the use of this cutpoint compared with the current standard could double the number of CCHDs that are identified based on NT risk.

Risk of selected structural abnormalities in infants after increased nuchal translucency measurement

OBJECTIVE

We sought to examine the association between increased first-trimester fetal nuchal translucency (NT) measurement and major noncardiac structural birth defects in euploid infants.

STUDY DESIGN

Included were 75,899 singleton infants without aneuploidy or critical congenital heart defects born in California in 2009 through 2010 with NT measured between 11-14 weeks of gestation. Logistic binomial regression was employed to estimate relative risks (RRs) and 95% confidence intervals (CIs) for occurrence of birth defects in infants with an increased NT measurement (by percentile at crown-rump length [CRL] and by ≥3.5 mm compared to those with measurements <90th percentile for CRL).

RESULTS

When considered by CRL adjusted percentile and by measurement ≥3.5 mm, infants with a NT ≥95th percentile were at risk of having ≥1 major structural birth defects (any defect, RR, 1.6; 95% CI, 1.3-1.9; multiple defects, RR, 2.1; 95% CI, 1.3-3.4). Infants with a NT measurement ≥95th percentile were at particularly high risk for pulmonary, gastrointestinal, genitourinary, and musculoskeletal anomalies (RR, 1.6-2.7; 95% CI, 1.1-5.4).

CONCLUSION

Our findings demonstrate that risks of major pulmonary, gastrointestinal, genitourinary, and musculoskeletal structural birth defects exist for NT measurements ≥95th percentile. The ≥3-fold risks were observed for congenital hydrocephalus; agenesis, hypoplasia, and dysplasia of the lung; atresia and stenosis of the small intestine; osteodystrophies; and diaphragm anomalies.

Obstetric, perinatal, and fetal outcomes in pregnancies with false-positive integrated screening results

OBJECTIVE

To assess the risk of adverse obstetric, perinatal, and fetal outcomes for pregnant women participating in prenatal sequential integrated screening through the California Prenatal Screening Program who had a false-positive screening result.

METHODS

Women who underwent first- and second-trimester prenatal integrated screening plus nuchal translucency measurement with outcome information available were included. Fetuses and neonates with chromosomal or neural tube defects were excluded. We compared the risk of adverse outcomes for all women with a positive screening result compared with a 10% random sample of women with a negative screening result. Logistic binomial regression was used to compare adverse outcomes in screen-positive compared with screen-negative women.

RESULTS

We identified 9,051 screen-positive and 30,928 screen-negative pregnancies with outcome information available. Compared with screen-negative pregnancies, screen-positive women were more likely to be diagnosed with preeclampsia, placenta previa, or abruption (7.6% screen-positive, 3.8% screen-negative; relative risk 1.7, 95% confidence interval [CI] 1.6-1.8) or experience fetal loss before 20 weeks of gestation (1.9% screen-positive, 0.2% screen-negative; relative risk 3.5, 95% CI 3.2-3.8). Women with positive results for more than one screened condition were at substantially greater risk of fetal and neonatal mortality (relative risks 33.6-156.7, 95% CIs 21.8-194.4).

CONCLUSION

Among pregnancies without chromosomal or neural tube defects, prenatal sequential integrated screening provides information regarding risk across a variety of adverse pregnancy outcomes.

Association of early-preterm birth with abnormal levels of routinely collected first- and second-trimester biomarkers

OBJECTIVE

The purpose of this study was to examine the relationship between typically measured prenatal screening biomarkers and early-preterm birth in euploid pregnancies.

STUDY DESIGN

The study included 345 early-preterm cases (<30 weeks of gestation) and 1725 control subjects who were drawn from a population-based sample of California pregnancies who had both first- and second-trimester screening results. Logistic regression analyses were used to compare patterns of biomarkers in cases and control subjects and to develop predictive models. Replicability of the biomarker early-preterm relationships that was revealed by the models was evaluated by examination of the frequency and associated adjusted relative risks (RRs) for early-preterm birth and for preterm birth in general (<37 weeks of gestation) in pregnancies with identified abnormal markers compared with pregnancies without these markers in a subsequent independent California cohort of screened pregnancies (n = 76,588).

RESULTS

The final model for early-preterm birth included first-trimester pregnancy-associated plasma protein A in the ≤5th percentile, second-trimester alpha-fetoprotein in the ≥95th percentile, and second-trimester inhibin in the ≥95th percentile (odds ratios, 2.3-3.6). In general, pregnancies in the subsequent cohort with a biomarker pattern that were found to be associated with early-preterm delivery in the first sample were at an increased risk for early-preterm birth and preterm birth in general (<37 weeks of gestation; adjusted RR, 1.6-27.4). Pregnancies with ≥2 biomarker abnormalities were at particularly increased risk (adjusted RR, 3.6-27.4).

CONCLUSION

When considered across cohorts and in combination, abnormalities in routinely collected biomarkers reveal predictable risks for early-preterm birth.