Seasonal impact in the frequency of isolated spina bifida

Objectives: To evaluate whether a relationship exists between season at conception and occurrence of isolated spina bifida (ISB). Study design: All fetuses with prenatal diagnosis of ISB were analyzed according to date of conception. We compared the seasonal rates of conception between ISB fetuses and a control group consisting of a cohort of fetuses delivered during the same period from 1992 to 2009. Results: In the control group, conceptions were equally distributed among the four seasons. Chi-square analysis showed a significantly higher rate of ISB conceptions in the fall compared with the control group (16/36, 44% vs 12467/50533, 25%, Odds Ratio (OR) 2.44, 95% confidence interval 1.21-4.92). Not a single woman with a fetus affected by ISB took preconceptional supplement of folic acid. Conclusions: Seasonality affects the frequency of ISB. We hypothesize that the seasonal differences may reflect dietary and climate changes with reduced intake of folic acid in the fall. © 2013 John Wiley & Sons, Ltd.