To determine the effect of preconceptional folate supplementation on duration of pregnancy and incidence of preterm delivery.
In a cohort of 38,033 singleton pregnancies preconceptional folate supplementation was prospectively recorded in the first trimester of pregnancy. Duration of pregnancy was estimated based on ultrasound measurement of crow-rump length between 10 4/7 and 13 6/7 weeks of pregnancy. Natural length of pregnancy was defined as gestational age at delivery in pregnancies uncomplicated by medical or obstetrical complications which may constitute indication for delivery. Pregnancies with those conditions: congenital or chromosomal abnormalities, termination of pregnancy or stillbirth, chronic hypertension, pregnancy induced hypertension, preeclampsia, gestational or pre-gestational diabetes, placental abruption and placenta previa, were censored. The effect of preconceptional folate supplementation on duration of pregnancy was evaluated using survival analysis-Cox regression.
Preconceptional folate supplementation for >= 1 year was associated with a 70% decrease in the incidence of spontaneous preterm delivery between 20 and 28 weeks (HR, 95% CI = 0.22, 0.08-0.62; p=0.004) and 50% decrease in the incidence of spontaneous preterm delivery between 28 and 32 weeks (HR, 95% CI = 0.45, 0.23-0.85; p=0.015). Adjustment for maternal characteristics: age, race, education, marital status and prior preterm birth, did not have a material effect. Preconceptional folate supplementation did not have a significant effect on duration of pregnancy beyond 32 weeks or if supplementation lasted < 1 year. The interaction term between folate supplementation and prior preterm birth was not significant (p=0.6). Proportional hazard assumption was met (p>0.05 for all).
Preconceptional folate supplementation is associated with a 50-70% reduction in the incidence of early spontaneous preterm birth. The earlier the preterm birth the stronger the effect. Folate supplementation is equally effective in patient with and without prior preterm birth.
© 2007 Mosby, Inc. Published by Elsevier Inc. All rights reserved.