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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 > or =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 priori 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.