Amount of folic acid supplementation, dietary and total folate intake (FFQ data) and hazard ratios for spontaneous PTD (22+0-36+6 weeks, n = 1,628). Cox regression for 65,668 participants in the Norwegian Mother and Child Cohort Study (2002–2009). Iatrogenic deliveries have been censored in the regression model.
1 HR per 500 μg extra folate/d.
2 Cox regression, adjusted for maternal age, prepregnancy BMI, parity, history of PTD and spontaneous abortion, child’s sex, smoking habits and alcohol consumption during pregnancy, maternal education, marital status, household income, energy intake. Mutual adjustment for dietary and supplemental folate intake.