UNCONJUGATED ESTRIOL AS MATERNAL SERUM MARKER FOR THE DETECTION OF DOWN-SYNDROME PREGNANCIES

The effectiveness of unconjugated estriol (uE(3)) as a serum marker fo r the detection of Down syndrome (DS) during the 2nd trimester of preg nancy was evaluated. A population of 18,764 normal singleton pregnanci es was screened for alpha-fetoprotein and human chorionic gonadotropin . In 9,311 women, uE(3) was added. Using a risk of 1:250 at term as a cutoff value, the false-positive rates were 4.1 and 4.3% without and w ith uE(3), respectively. The detection rates in 47 DS serum samples, s ome of which were studied retrospectively, were 66% without uE(3) and 57% with uE(3). In 12 of 25 younger women and in 19 of 22 older women, DS was detected without uE(3). The uE(3) contributed to the detection of 4 additional DS pregnancies (1 in the young and 3 in older women). On the other hand, 8 DS pregnancies (3 in younger women and 5 in olde r women) escaped detection. In our sample the addition of uE(3) lowere d the detection rate of DS pregnancies with only a small and insignifi cant effect on the false-positive rate. Our results call for special c aution in the addition of markers for risk calculations. We suggest th at pregnancies with a calculated risk of >1:250 following maternal ser um alpha-fetoprotein and human chorionic gonadotropin markers tests sh ould be regarded as high-risk pregnancies, even in cases in whom the a ddition of uE(3) lowers the risk beneath the cutoff value.