OBJECTIVE. To determine the sensitivity and false-positive rate of Down syn
drome 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 Janu
ary 1992 to January 2000 for the following criteria: known Down syndrome fe
tus or newborn, advanced maternal age, and genetic sonogram from 14-24 week
s' gestation. The a prior! maternal age or maternal serum screen risk was m
odified by likelihood ratios for ultrasound markers. Without markers the ri
sk was reduced by 50%. The cut-off was 1:270.
RESULTS. Age and maternal serum screen had a sensitivity of 90.5% and a fal
se-positive rate of 27.1%. Age and ultrasound had a 95.2% sensitivity and 4
3.5% false-positive rate, whereas the combination of age, maternal serum sc
reen, and ultrasound had a 97.6% sensitivity and a 22.0% false-positive rat
e.
CONCLUSION: The combination of age, maternal serum screen, and ultrasound i
mproves the sensitivity for Down syndrome detection in the advanced materna
l age population.