Folic acid supplementation in early pregnancy and asthma in children aged 6 years.

Design: Prospective cohort. Participants: 1,499 pregnant women from Massachusetts and Connecticut; followed through pregnancy and offspring to age 6; subset included women with asthma history or symptoms; data collected via interviews and medical records; analysis used logistic regression adjusting for confounders.

Daily folic acid supplementation during the month before conception through the third month of pregnancy; prenatal vitamins contain 800 mcg folic acid per tablet and other vitamin supplements contain 400 mcg per tablet.

No association between folic acid supplementation in early pregnancy and asthma in offspring by age 6. The adjusted odds ratio per 100 mcg increase in average daily intake during the first trimester was 0.98 (95% CI: 0.93-1.04). Across time periods and intake categories (0, <400 mcg, 400-800 mcg, >800 mcg) there was no significant dose-response relationship (p-trend > 0.05). Conclusion: Evidence does not support folic acid supplementation in pregnancy altering asthma risk in offspring by age 6.

No dietary folate data; small number in >800 mcg category; asthma outcome may be misclassified; potential residual confounding; observational design; fortification effects not fully accounted.