A prospective trial of prenatal screening for Down syndrome by means of maternal serum α-fetoprotein, human chorionic gonadotropin, and unconjugated estriol

OBJECTIVE: Our purpose was to prospectively evaluate the effectiveness of prenatal screening for Down syndrome by means of multiple serum markers. STUDY DESIGN: α-Fetoprotein, human chorionic gonadotropin, and unconjugated estriol were measured in 8233 midtrimester serum samples, including 7492 from women <35 years old and 741 from women ≥35 years old. Down syndrome risks were computed by means of age and all three markers. Further testing was recommended for patients with a risk ≥ 1: 270. Testing for trisomy 18 was recommended for patients with an a-fetoproteln ≤ 0.70 multiples of the median, human chorionic gonadotropin ≤0.50 multiples of the median, and unconjugated estriol ≤0.55 multiples of the median. RESULTS: Of women screened initially 10.4% had a Down syndrome risk ≥1:270; 10 of 12 known cases of Down syndrome were identified, One abnormality was detected for every 33 amniocenteses performed in this group. Of 0.4% of patients at increased risk for trisomy 18, two cases of trisomy 18 and one of triploidy were found. CONCLUSION: Multiple marker screening is effective in identifying the majority of fetal chromosome anomalies.