Amniotic fluid alpha-fetoprotein levels and the prenatal diagnosis of neural tube defects: a collaborative study of 2180 pregnancies in the Netherlands.

Amniotic fluid alpha-fetoprotein (AFP) concentrations were measured in 2180 patients at risk of fetal abnormality because of previous history, family history, advanced maternal age, suspected fetal growth retardation and hydramnios. In 12 patients investigated before 20 weeks gestation, pregnancy was terminated because of a raised amniotic fluid AFP-level: 11 fetuses had neural tube defects (NTDs) and one had a congenital nephrosis. There were no false negative results in the 1927 patients tested before 20 weeks and with a pregnancy of known outcome. In patients tested after 20 weeks, the amniotic fluid AFP concentration was raised in 20 cases of anencephaly, in 9 fetuses with severe congenital malformations without NTD and in one apparently normal fetus. Of 428 patients with a previous offspring who had a NTD, only 8(1.9 per cent) again had a fetus with a NTD.