Evaluation of measurement of maternal plasma alpha-fetoprotein levels as a screening test for fetal neural tube defects.

Maternal plasma alpha-fetoprotein (AFP) levels were estimated on 1844 consecutive patients at the time of their first hospital antenatal visits. There were 28 pregnancies with an 'abnormal' outcome: 19 patients had twins, 3 had an anencephalic fetus, and 6 a fetus with a spina bifida (4 of these had an open neural tube defect). Evaluation of maternal plasma AFP levels as a screening test for neural tube defects at 15 to 19 weeks gestation indicated a sensitivity of 50% taking the 'cut-off' point as the 95th centile of the plasma AFP levels in pregnancy with a normal outcome.