Understanding the increased risk of neural tube defect-affected pregnancies among Mexico-born women in California: immigration and anthropometric factors.

Mexico-born women in the United States have an unexplained twofold increased risk of neural tube defect (NTD)-affected pregnancies. We examined whether immigration characteristics were associated with the NTD risk and whether anthropometric factors contributed to the increased risk among Mexico-born women. Data were derived from a large population-based case-control study in California. In-person interviews were conducted with mothers of 538 (88% of eligible) NTD-affected fetuses/infants and mothers of 539 (88%) randomly selected non-malformed control infants. The crude odds ratio (OR) for NTDs among all Mexico-born women, women residing <2 years in the US, and women >16 years old at immigration compared with non-Hispanic white women was 2.4 [95% confidence interval (CI) = 1.8, 3.3], 7.2 [95% CI = 3.7, 14.0] and 3.0 [95% CI = 2.0, 4.4], respectively. Risk for second- or third-generation Mexican-Americans was similar to that of white women. The crude OR for all Mexico-born women was reduced from 2.4 to 2.0 [95% CI = 1.3, 3.0] and for those residing <2 years in the US from 8.4 to 7.1 [95% CI = 3.2, 15.3] after adjustment for maternal body mass index (BMI), height, compromised diet, diabetes, and other known risk factors. In term pregnancies, additional adjustment for pregnancy weight gain reduced the OR in all Mexico-born women and recent immigrants by 16% and 25%, respectively. Low pregnancy weight gain (<10 vs. 10-14 kg) was particularly associated with increased NTD risk among Mexico-born women (OR(ADJ) = 5.8; 95% CI = 2.1, 15.8). Findings indicate that recent Mexican immigrants have a sevenfold increased risk for NTDs. Maternal BMI and height contributed very little, and inadequate weight gain contributed modestly to the NTD risk disparity for Mexican immigrants.