Maternal serum α-fetoprotein screening for chromosomal abnormalities: A prospective study in women aged 35 and older

Abstract

OBJECTIVE: Our purpose was to determine the detection and false-positive rates for maternal serum α-fetoprotein measurement to screen for fetal Down syndrome and other chromosomal abnormalities in women ≥35 years old. STUDY DESIGN: A total of 3896 women had serum maternal serum α-fetoprotein levels measured routinely before amniocentesis for the indication of advanced maternal age. RESULTS: Eighty-five percent (28/33) of fetal Down syndrome pregnancies had second-trimester risks of ≥1:270 on the basis of a combination of maternal serum α-fetoprotein measurement and maternal age. Risks were also ≥1:270 in 63% of the unaffected pregnancies. Sex chromosome aneuploidies, translocations, and other nonautosomal chromosome abnormalities in this study population were not associated with altered maternal serum α-fetoprotein levels; 51.9% (14/27) of these, however, were also assigned risks of ≥1:270. CONCLUSIONS: Maternal serum α-fetoprotein screening is more accurate than age alone for assigning individual Down syndrome risk in pregnant women ≥35 years old. Counseling for women in this age group should include information regarding the lower sensitivity of maternal serum α-fetoprotein screening for detecting fetal Down syndrome and other chromosomal abnormalities (especially sex chromosome aneuploidies) compared with offering amniocentesis to these women. (AM J OBSTET GYNECOL 1994; 170:80.)