Antenatal screening in Oxford for fetal neural tube defects.

Between May 1975 and the end of 1977, 6443 antenatal patients were screened mainly between 16 and 22 weeks of pregnancy for neural tube defects (NTDs) at the John Radcliffe Hospital, Oxford, by maternal serum alpha-fetoprotein (AFP) measurement; a take-up of 72 per cent. Seventeen out of 18 (94 per cent) patients with open NTD pregnancies (9 out of 9 with anencephaly and 8 out of 9 with open spina bifida) had positive screening tests, and all except one were offered and accepted a termination of pregnancy. Two hundred and forty-five (3.8 per cent) patients with unaffected pregnancies also had positive screening tests, although only 1.4 per cent had an amniocentesis. Following ultrasonography, about 50 per cent of patients with unaffected pregnancies with positive screening tests were not offered an amniocentesis because they had a multiple pregnancy or their gestational age had been underestimated. The odds of having a fetus with an NTD among the women who had an amniocentesis was about 1 to 6 (1 to 11 for open spina bifida alone). Two apparently normal pregnancies were terminated. A survey of the acceptability of the screening programme among a consecutive sample of 73 patients who knew that they had a positive screening test revealed that all except one had no objection to screening in general, and 68 (93 per cent) wanted to be tested again in a future pregnancy. The approximate direct cost of the programme was 2 pounds to 3 pounds per patient screened, or about 1000 pounds per NTD detected (about 2200 pounds per open spina bifida detected).