OBJECTIVE: To investigate the association of maternal circulating 25‐hydroxyvitamin D3 [25(OH)D3] concentration with pregnancy and birth outcomes.
DESIGN: Prospective cohort study.
SETTING: Four geographical areas of Spain, 2003–2008.
POPULATION: Of 2382 mother–child pairs participating in the INfancia y Medio Ambiente (INMA) Project.
METHODS: Maternal circulating 25(OH)D3 concentration was measured in pregnancy (mean [SD] 13.5 [2.2] weeks of gestation). We tested associations of maternal 25(OH)D3 concentration with pregnancy and birth outcomes.
MAIN OUTCOME MEASURES: Gestational diabetes mellitus (GDM), preterm delivery, caesarean section, fetal growth restriction (FGR) and small‐for‐gestational age (SGA), anthropometric birth outcomes including weight, length and head circumference (HC).
RESULTS: Overall, 31.8% and 19.7% of women had vitamin D insufficiency [25(OH)D3 20–29.99 ng/ml] and deficiency [25(OH)D3 < 20 ng/ml], respectively. After adjustment, there was no association between maternal 25(OH)D3 concentration and risk of GDM or preterm delivery. Women with sufficient vitamin D [25(OH)D3 ≥ 30 ng/ml] had a decreased risk of caesarean section by obstructed labour compared with women with vitamin D deficiency [relative risk (RR) = 0.60, 95% CI 0.37, 0.97). Offspring of mothers with higher circulating 25(OH)D3 concentration tended to have smaller HC [coefficient (SE) per doubling concentration of 25(OH)D3, −0.10 (0.05), P = 0.038]. No significant associations were found for other birth outcomes.
CONCLUSION: This study did not find any evidence of an association between vitamin D status in pregnancy and GDM, preterm delivery, FGR, SGA and anthropometric birth outcomes. Results suggest that sufficient circulating vitamin D concentration [25(OH)D3 ≥ 30 ng/ml] in pregnancy may reduce the risk of caesarean section by obstructed labour.
