Avoidance of anencephalic and spina bifida births by maternal serum-alphafetoprotein screening.

Screening of 11 585 pregnant women between 16 and 20 completed weeks' gestation for raised serum-alphafetoprotein (A.F.P.) levels showed that the birth of 81.4% of babies with open neural-tube defects could be avoided. The screening test was sensitive enough to detect 93% of those affected and serum-A.F.P. levels above the point at which intervention shouldbe considered were found in 1.7% of pregnancies. After 75.2% of false-positives had been excluded by ultrasonography or by a repeat of the serum test, only 0.63% of pregnancies proceeded to amniocentesis, 46.6% of amniocenteses showed raised amniotic A.F.P. levels due to fetal abnormality. Fetal loss by abortion or perinatal death after amniocentesis occurred in 0.034% of pregnancies screeded, 75% being associated with threatened abortion before amniocentesis. There were no terminations of normal pregnancies due to false-positive amniotic A.F.P. results. It is concluded that voluntary maternal serum-A.F.P. screening has a valuable role in antenatal care.