Fetal sex determination from maternal plasma in pregnancies at risk for congenital adrenal hyperplasia

OBJECTIVE: To determine first-trimester fetal sex by isolating free fetal D NA from maternal plasma. METHODS: The index case was a pregnant woman who previously delivered a gir l with congenital adrenal hyperplasia. The SRY gene as a marker for the fet al Y chromosome was detected in maternal serum and plasma by quantitative p olymerase chain reaction analysis. Simultaneously, we performed the same te st in 25 and 19 women in the first and second trimester, respectively, and compared plasma results with fetal gender as assessed by prenatal karyotypi ng or as seen at ultrasound or birth. RESULTS: In 44 of 45 patients at gestational ages ranging from 8 3/7 to 17 3/7 weeks, we correctly predicted fetal sex using quantitative polymerase c hain reaction analysis of the SRY gene in maternal plasma. In one case, the test result was inconclusive. Overall, fetal sex was correctly predicted i n 97.8% of cases (95% confidence interval 88.2%, 99.9%). CONCLUSION: Amplification of free fetal DNA in maternal plasma is a valid t echnique for predicting fetal sex in early pregnancy. In case of pregnancie s at risk for congenital adrenal hyperplasia, the technique allows restrict ion of dexamethasone treatment to female fetuses resulting in a substantial decrease of unnecessary treatment and invasive diagnostic tests. (C) 2001 by the American College of Obstetricians and Gynecologists.