Risk of oral clefts in relation to prepregnancy weight change and interpregnancy interval.

Epidemiologic evidence regarding the influence of maternal obesity on the risk of oral clefts is inconsistent. It is unknown whether increases in maternal weight before pregnancy are related to the risk of these malformations. The authors conducted a population-based cohort study in Sweden among 220,328 women who had their first two pregnancies between 1992 and 2004. The risk of oral clefts during the second pregnancy was estimated in relation to maternal change in body mass index (BMI; weight (kg)/height (m)(2)) from the beginning of the first pregnancy to the beginning of the second pregnancy. Among women whose second-pregnancy BMI was > or =3 units higher than their first-pregnancy BMI, the adjusted risk of isolated cleft palate was 2.3 times higher (95% confidence interval: 1.4, 4.0) as compared with women whose BMI did not change substantially. BMI change was not related to the risk of cleft lip. Unexpectedly, the birth prevalence of isolated cleft palate per 1,000 livebirths increased linearly with the length of the interpregnancy interval, from 0.3 in women with intervals of <12 months to 0.9 in women with intervals of > pr =48 months (adjusted p for trend = 0.002). High prepregnancy maternal weight gain and long interpregnancy intervals appear to be associated with increased risk of cleft palate.