Objectives: To conduct surveillance for neural tube defects (NTDs) in a high-risk region of the United States and to prevent occurrence and recurrence of NTDs through the periconceptional use of folic acid supplements.

Design: Active and passive methods were used for surveillance of NTD-affected pregnancies and births during a 6-year period (October 1992-September 1998). Individual genetic counseling was used to prevent NTD recurrences and a public awareness campaign was used to reduce NTD occurrences.

Setting: State of South Carolina.

Patients: All cases of spina bifida, anencephaly, and encephalocele identified among 278 122 live births and fetal deaths to South Carolina residents during 1992-1998 were included.

Main outcome measure: Changes in occurrence and recurrence rates during a 6-year period.

Results: Over the 6 years of surveillance, the prevalence rates for NTDs decreased from 1.89 to.95 cases per 1000 live births and fetal deaths. The prevalence decrease is explained primarily by a decrease in cases of spina bifida. Isolated NTDs accounted for 297/360 (82%) NTDs and 63/360 (18%) had at least 1 other structural anomaly. Females predominated among isolated NTDs but the sex distribution was equal among NTD cases with other anomalies. Prevalence rates for whites (1.48 cases per 1000 live births and fetal deaths) were higher than rates for blacks (.87 cases per 1000 live births and fetal deaths). There were no NTD recurrences in 113 subsequent pregnancies to mothers of infants with isolated NTDs who took periconceptional folic acid. The rate of periconceptional folic acid use among women of childbearing years increased from 8% to 35% during the 6-year project period.

Conclusion: The prevalence of NTDs in a high-risk region has declined coincident with the increased periconceptional use of folic acid supplements among women of childbearing age.neural tube defects, high-risk region, birth defects, folic acid, spina bifida, anencephaly, encephalocele.