Folate Levels by Time Since Last Live Birth Among U.S. Women, 2007-2016

Folate depletion in the postpartum period may increase the risk of adverse pregnancy outcomes for women with a short interpregnancy interval following a live birth. We sought to examine folate levels by time since last live birth among U.S. women. Data were from 4,809 U.S. women, 20-44 years of age, participating in the National Health and Nutrition Examination Survey, 2007-2016. Red blood cell (RBC) folate was measured using microbiological assay on whole blood samples. Dietary folate intake and folic acid supplementation were measured during a 24-hour dietary recall. Prevalence of supplementation by time since last live birth was estimated from logistic regression models; mean levels of RBC folate and mean intake of dietary folate equivalent were estimated from linear regression models. Models were adjusted for maternal sociodemographic characteristics. In adjusted models, supplementation (±standard error) was highest among women in the first year postpartum (31.7% ± 3.2) compared with nulliparous women (23.7% ± 1.9) and those 2-3 years (15.6% ± 1.9) and ≥3 years (18.4% ± 1.6) after last live birth. Mean RBC folate was highest among women in the first year postpartum, regardless of supplementation, with overall mean levels of 606 ± 15 ng/mL, compared with 484 ± 9, 477 ± 11, and 474 ± 7 among women in the aforementioned groups, respectively. Mean dietary folate intake was also highest among postpartum women: 542 ± 23 mcg/day, compared with 474 ± 12, 486 ± 21, and 467 ± 12. Folate levels are highest in the first year postpartum compared with other time periods within a woman's reproductive lifespan. These findings do not support the idea that postpartum U.S. women are depleted in folate, on average.