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.