Maternal vitamin D status, prolonged labor, cesarean delivery and instrumental delivery in an era with a low cesarean rate.

Objective: To examine the association between maternal 25-hydroxyvitamin D (25(OH)D) and adverse labor and delivery outcomes.
Study Design: We measured serum 25(OH)D at ⩽ 26 weeks gestation in a random subsample of vertex, singleton pregnancies in women who labored (n=2798) from the 12-site Collaborative Perinatal Project (1959 to 1966). We used labor and delivery data to classify cases of adverse outcomes.
Result: Twenty-four percent of women were vitamin D deficient (25(OH)D <30 nmol l(-1)), and 4.5, 3.3, 1.9 and 7.5% of women had prolonged stage 1 labor, prolonged stage 2 labor, primary cesarean delivery or indicated instrumental delivery, respectively. After adjustment for prepregnancy body mass index, race and study site, 25(OH)D concentrations were not associated with risk of prolonged stage 1 or 2, cesarean delivery or instrumental delivery.
Conclusion: Maternal vitamin D status at ⩽ 26 weeks was not associated with risk of prolonged labor or operative delivery in an era with a low cesarean rate.