Clinical impact of systematic genetic sonogram screening in a low-risk population

OBJECTIVE: To determine the clinical impact of a genetic sonogram (GS) on a population at low risk for trisomy 21 (T21). STUDY DESIGN: A GS evaluating common major and minor markers was created and prospectively applied to consecutive women at 15-20 weeks' gestation presenting for routine ultrasound and at low T21 risk. Prenatal diagnosis (PND) referral occurred if 1 major marker, 2 minor markers, major malformation or choroid plexus cysts (CPCs) were seen. Neonatal outcomes were determined by chart review for neonates born at our institution and by letter for those born elsewhere. Using an ultrasound database, a similar population was identified prior to study inception and the GS retrospectively applied. PND referrals in both periods were confirmed by chart review. The rates of isolated minor marker (IMM), positive GS and PND referrals were compared using χ ² analysis. RESULTS: IMM detection was unchanged (43 of 434, 10.1%) in the study vs. (23 of 243, 9.5%) control group. Excluding CPCs, 6 of 18 (33.3%) subjects of vs. 2 of 28 (7.1%) controls with IMM were referred for prenatal diagnosis (p < 0.03). The frequency of positive GS was unchanged: 14 of 434 (3.2%) subjects vs. 5 of 243 (2.1%) controls. CONCLUSION: Currently no prospectively studied, effective ultrasound models exist for screening low-risk populations at 15-20 weeks. A GS with clear criteria for counseling on an increased T21 risk decreased inappropriate referrals without increasing positive screens.