Ultrasonography in patients with low maternal serum alpha-fetoprotein.

In previous reports on the use of maternal serum alpha-fetoprotein (MSAFP), emphasis was placed on the significance of elevated MSAFP values. The purpose of this paper is to stress the importance of low MSAFP values based on data from 28,285 pregnancies screened. The cutoff value used to define low MSAFP is less than 5 ngm/ml or 0.2 multiples of the median at 16 weeks. In the low group, which comprised 1.3% of the total screened, the findings at ultrasonography were incorrect gestational age, fetal demise, hydatid mole, nonpregnancy, and a grossly normal live fetus. The overall incidence of a positive finding (exclusive of a normal fetus) in the low MSAFP group was 83% compared to an incidence of 38% of the patients offered ultrasonography in the group with elevated MSAFP. The low MSAFP group is more likely to yield a finding that could affect obstetrical management than the high MSAFP group.