Role of ultrasound for Down syndrome screening in advanced maternal age

OBJECTIVE. To determine the sensitivity and false-positive rate of Down syndrome screening by use of maternal serum screen and the genetic sonogram in women greater than or equal to 35 years of age. STUDY DESIGN: We searched our perinatal databases retrospectively from January 1992 to January 2000 for the following criteria: known Down syndrome fetus or newborn, advanced maternal age, and genetic sonogram from 14-24 weeks' gestation. The a prior! maternal age or maternal serum screen risk was modified by likelihood ratios for ultrasound markers. Without markers the risk was reduced by 50%. The cut-off was 1:270. RESULTS. Age and maternal serum screen had a sensitivity of 90.5% and a false-positive rate of 27.1%. Age and ultrasound had a 95.2% sensitivity and 43.5% false-positive rate, whereas the combination of age, maternal serum screen, and ultrasound had a 97.6% sensitivity and a 22.0% false-positive rate. CONCLUSION: The combination of age, maternal serum screen, and ultrasound improves the sensitivity for Down syndrome detection in the advanced maternal age population.