Screening for fetal neural tube defects by maternal plasma alpha-fetoprotein determination.

A total of 5539 consecutive pregnant patients at three maternity units in the City and Hackney District of London were screened for fetal neural tube defect by measurement of maternal plasma alpha-fetoprotein (AFP) levels. Only 25-7% of women booked at 16 to 22 weeks, the optimum time for this screening test; 54-1% booked before 16 weeks and 20-2% after 22 weeks. Of the women tested before 23 weeks, 300 had elevated levels of AFP in plasma and 14 of them had fetuses with abnormalities known to cause a rise in AFP levels (12 fetuses had a neural tube defect and 2 had alimentary tract abnormalities). Of women examined before 23 weeks, half of those with twin pregnancies had elevated levels of plasma AFP as did 16-7% of those who ultimately had a spontaneous abortion.