Impact of prenatal diagnosis and elective termination on prevalence and risk estimates of neural tube defects in California, 1989-1991.

The authors examined the impact of prenatal diagnosis and elective termination of neural tube defect (NTD)-affected pregnancies on NTD prevalence and risk estimates. Prevalence data were actively ascertained and were derived from a population-based 1989-1991 cohort of California births. Included were 664 singleton infants/fetuses with an NTD. The birth prevalence (livebirths and stillbirths only) was 48.4% of the total prevalence (including elective terminations) for anencephaly and 70.2% for spina bifida. The authors also used in-person interview data from mothers of 538 of the ascertained NTD cases and mothers of 539 randomly selected nonmalformed control infants to examine maternal/infant characteristics. Compared with women who delivered liveborn/stillborn infants with an NTD, women who electively terminated NTD-affected pregnancies were disproportionately white, were more highly educated, had higher incomes, and used vitamins containing folic acid more often. For factors associated with elective terminations, risk estimates appeared biased when only liveborn and stillborn infants were included among cases compared with analyses in which all clinically recognized NTD-affected pregnancies were included.