Abstract
Objective The objective of this study was to evaluate risk factor prevalence in pregnancies
with fetal Down syndrome, in an effort to characterize efficacy of population-based
screening.
Study Design Retrospective review of singleton pregnancies with delivery of live born or stillborn
infant with Down syndrome from 2009 through 2015. Risk factor categories included
maternal age ≥35 years, abnormal serum screening, identification of ≥1 ultrasound
marker at 16 to 22 weeks (nuchal thickness ≥6 mm, echogenic intracardiac focus, echogenic
bowel, renal pelvis dilatation, femur length <third percentile), and detection of
a major fetal anomaly. Statistical analyses included χ2 test and Mantel–Haenszel χ2 test.
Results Down syndrome infants represented 1:428 singleton births. All risk categories were
assessed in 125 pregnancies and included abnormal serum screen in 110 (88%), ≥1 ultrasound
marker in 66 (53%), and ≥1 anomaly in 41 (34%). The calculated risk was at least 1:270
in 93% of Down syndrome pregnancies. More pregnancies had multiple risk factors than
had a single risk factor, 90 (72%) versus 30 (24%), p < 0.001. An abnormal ultrasound marker or anomaly was identified in >50% of fetuses
in women <35 years and in >75% of those 35 years and older.
Conclusion In a population-based cohort, sensitivity of second-trimester Down syndrome screening
was 93%, with multiple risk factors present in nearly three-fourths of cases.
Keywords
Down syndrome - ultrasound markers - serum aneuploidy screening
