Amniotic fluid alpha1fetoprotein in the diagnosis of neural tract malformations.

Amniotic fluid alpha1fetoprotein levels were determined in 400 pregnancies. The normal range for alpha1fetoprotein in amniotic fluid was defined by 350 samples from normal pregnancies. Elevated levels of alpha1fetoprotein were detected in 17 out of 18 pregnancies which gave rise to infants with neural tract abnormalities. The significance of this test in the antenatal diagnosis of neural tract abnormalities is discussed together with the possible reasons for "false negative" and "false positive" results. There were no complications in an individual series of 105 consecutive amniocenteses.