Neural Tube Defect Surveillance and Folic Acid Intervention — Texas-Mexico Border, 1993-1998

Morbidity and Mortality Weekly Report, Jan 14, 2000

Neural tube defects (NTDs) are common and serious malformations that originate early in pregnancy. In the United States, approximately 4000 pregnancies each year are affected by the two most common NTDs (spina bifida and anencephaly). In 1992, the Texas Department of Health (TDH), with support from a CDC cooperative agreement, implemented the Texas Neural Tube Defect Project (TNTDP), a program of NTD surveillance and risk-reduction activities in the 14 counties that border Mexico. The project was initiated in response to an anencephaly cluster identified during 1990--1991 in Brownsville (Cameron County), Texas [1]. Whether the high anencephaly rate (19.7 per 10,000 live births) was unique to Cameron County or was characteristic of the entire border was unknown. This report summarizes NTD surveillance rates for the 14 Texas-Mexico border counties for 1993--1998 and presents preliminary results of TNTDP efforts to prevent the recurrence of NTDs by providing folic acid to high-risk women. Findings indicate that the baseline rate along the border is high (13.4 per 10,000 live births) and largely reflects the rate among Hispanics (13.8). Although a longer period is needed to obtain definitive results, folic acid appears to be effective for reducing the risk for NTD recurrence in Hispanics.

The TNTDP surveillance system involved prospective case finding (International Classification of Diseases, Ninth Revision [ICD-9], codes 740, 741, and 742.0, for all gestational ages) using the following data sources: hospitals; birthing centers; ultrasound centers; abortion centers; prenatal clinics; genetics clinics; and birth attendants including lay midwives, certified nurse midwives, and nonhospital physicians. Data on NTD cases were collected by three field teams (El Paso, Harlingen, and Laredo), abstracted onto standardized forms, and sent to TDH with confirmatory medical records. Denominator data (live birth, death, and fetal death records) were derived from the Bureau of Vital Statistics at TDH; 91% of the resident live births in the border counties were to Hispanic women of Mexican ancestry.

For 1993--1998, NTD surveillance rates include cases at all gestational ages for the 14 Texas-Mexico border counties (Table 1). The surveillance system identified 360 resident NTD-affected births/terminations (cases) not otherwise accompanied by a known trisomy, triploidy, or syndrome (e.g., Turner, Meckel, or amniotic band). Of these cases, 324 (90%) occurred in the four most populous border counties--Cameron, El Paso, Hidalgo, and Webb. The overall NTD rate in the border counties for 1993-1998 was 13.4 per 10,000 live births (6.1 for anencephaly, 6.3 for spina bifida, and 1.0 for encephalocele) (Table 1). The craniorachischisis (contiguous opening of brain and spinal column; included in anencephaly) rate in the border counties was 0.5.

Of the 360 women identified as having had an NTD-affected pregnancy, 340 (94.4%) were Hispanic. Of the 20 non-Hispanic women, 16 (4.4%) were white, three (0.8%) were black, and one (0.3%) was Asian/Pacific Islander. The rate among Hispanics was 13.8 per 10,000 live births and the rate among non-Hispanic whites was 8.8 (p=0.08). El Paso County (the northwesternmost county) had a significantly lower NTD rate (9.0) than the rest of the border counties combined (15.6; p[less than]0.001). The rate among Hispanics also was significantly lower for El Paso County (8.8) than that for the rest of the border counties (16.1) (p[less than]0.001).

Of the NTD-affected pregnancies, 68 (19%) were induced or spontaneously aborted at [less than]20 weeks' gestation, 94 (26%) were delivered or induced at 20 through 33 weeks' gestation, and 198 (55%) were delivered at [greater than or equal to]34 weeks' gestation. Excluding fetuses that failed to reach 20 weeks' gestation would have lowered the overall rate to 10.8 per 10,000 live births (p=0.01).

The primary objective of TNTDP is preventing recurrence of NTDs by providing folic acid to women who have had an NTD-affected pregnancy. For the folic acid intervention program, all women identified through the surveillance protocol were contacted by telephone, letter, and/or in person. Women whose index pregnancy was delivered or terminated in 1993 or later and who resided in the study area were asked to enroll in the program. The enrolled women were interviewed and provided preconception, pregnancy, and NTD risk-reduction education and counseling. If the women used contraception, they were given a multivitamin with 0.4 mg folic acid; if the women did not use contraception, they were given daily doses consisting of 4.0 mg folic acid--one multivitamin containing 1.0 mg of folic acid and three 1.0 mg tablets of folic acid. Women were followed, counseled, and provided folic acid supplements at 1- to 3-month intervals.

As of December 31, 1998, 264 (73%) of the 360 women were eligible for enrollment in the folic acid intervention program; 96 (27%) women were not eligible for enrollment (moved out of area or had tubal ligations/hysterectomies). Of the 264 eligible women, 95 (36%) refused enrollment, quit, or were lost to follow-up; 17 (6%) consented but were pending enrollment; and 152 (58%) were taking folic acid. Of 65 (34%) eligible women with induced abortions, 22 (34%) refused participation in the folic acid intervention compared with 19 (15%) of 128 (p=0.004) who had had natural outcomes (i.e., live-born infants, stillbirths, or spontaneous abortions).