Very low maternal plasma alpha-fetoprotein concentration. An indication for follow-up

In the course of a screening programme for the detection of fetal neural tube abnormalities by measurement of maternal plasma alpha-fetoprotein (AFP), 57 patients were identified who had plasma AFP levels of less than 7 units/ml at 15-20 weeks gestation. follow-up at the time of screening included requests to confirm that the patient was pregnant and also to repeat the AFP test. Tow patients were lost to follow-up and of the remaining 55, 17 patients (31 per cent) were subsequently shown not to have a live fetus and 31 patients (56 per cent) had incorrect estimates of gestation. No particular reason for the very low plasma AFP could be identified in the other seven patients.