Vitamin D during pregnancy and its association with birth outcomes: a Brazilian cohort study

Evidence is lacking on how variation in vitamin D concentrations during gestation affects perinatal outcomes. Therefore, we evaluated the association between vitamin D serum concentrations during pregnancy and neonatal outcomes.

A prospective cohort of 180 healthy Brazilian pregnant women was followed and plasma 25-hydroxyvitamin [25(OH)D, nmol/L] was measured at 5-13 (baseline), 20-26 and 30-36 gestational weeks. Birth weight (BW), birth length (BL), BW z-scores, BL z-scores, first minute Apgar, small for gestational age (SGA), large for gestational age (LGA) and preterm birth were the outcomes. Multiple linear and Poisson regression models were estimated. Best linear unbiased prediction of random coefficients model was used to determine the association between the mean rate of change in vitamin D during pregnancy concentrations and neonatal outcomes.

Mean (SD) BW was 3300 (600) g, BW z-score 0.34 (1.11), BL 49.3 (3.3) cm, BL z-score 0.44 (1.5), and first minute Apgar score 8.2 (1.4). Prevalence of SGA, LGA and preterm birth were 6%, 18% and 13%, respectively. 25(OH)D was directly associated with the risk of preterm birth at all trimesters. Incidence-rate ratios were 1.02, 1.05 and 1.04 for the 1st, 2nd and 3rd trimester, respectively. Mean rate of change during pregnancy in 25(OH)D was directly associated with BW z-score (β: 0.36, 95% CI 0.07; 0.65), LGA risk (IRR: 1.97, 95% CI 1.07; 3.63) and preterm birth (IRR: 7.35, 95% CI 2.99; 18.07).

Mean 25(OH)D rate of change during pregnancy was directly associated with BW z-scores, and increased LGA and preterm birth risk.