Efficacy of community-based second trimester genetic ultrasonography in detecting the chromosomally abnormal fetus

We sought to assess prospectively the efficacy of community-based genetic u ltrasonography in detecting chromosomally abnormal fetuses in a high-risk p opulation and determine independent markers of aneuploidy. Patients 18 year s old and older who were between 14 and 24 weeks' gestation were included i f referred for maternal age greater than 35 years, increased risk of Down s yndrome or trisomy 18 by second trimester serum screen, or prior affected o ffspring. All women had a targeted ultrasonographic examination between Apr il 1997 and Tune 1999 and were offered fetal chromosomal analysis. Markers of aneuploidy and pregnancy outcomes were recorded prospectively. The prima ry outcome was prenatally or postnatally detected chromosomal abnormalities . Of the 1030 fetuses seen during the study, 789 had outcome data available and constituted the study group. In this group, 694 (87.9%) ultrasonograms were normal, 73 (9.2%) had one marker present, 17 (2.2%) had two markers p resent, and 5 (0.6%) had three or more markers present. Fourteen of 17 (82. 3%:) aneuploid fetuses had an abnormal ultrasonogram tone or more markers p resent), including 5 of 7 (71.4%) with Down syndrome. Logistic regression s howed abnormal four-chamber view, structural anomaly and intracardiac echog enic focus to be significant aneuploidy markers. The amniocentesis rate was 334 of 1030 (32.4%,), and it increased with the number of sonographic mark ers noted (0 = 29.9%, 1 = 60.2%, 2 = 70.6%;, 3 or more 80%). Genetic ultras onography is highly effective in identifying chromosomally abnormal fetuses in a community-based practice.