Introduction Factors which increase risk of delivery by cesarean include older maternal age, obesity, nulliparity, minority status and a prior history of cesarean delivery. In all probability less well defined factors exist at least one of which may be nutritional—maternal vitamin D deficiency and insufficiency during pregnancy. We examined the association of circulating levels of vitamin D to risk of cesarean delivery using prospective data.

Method Circulating maternal 25-hydroxyvitamin D and intact parathyroid hormone at entry to care (13.8±0.17 weeks - mean, SEM) were assayed by HPLC (25 hydroxyvitamin D) and radioimmunoassay (parathyroid hormone) in a cohort of 1153 low income and minority gravidae from Camden, NJ.

Results The prevalence of vitamin D deficiency (19.8%) and insufficiency (50.5%) at entry was high and accompanied by increasing concentrations of parathyroid hormone, a functional indicator of vitamin D status. Risk for primary cesarean, for secondary cesarean, as well as for all deliveries by cesarean was increased approximately twofold for vitamin D deficient women (<37.5 nmol/l) except for primary cesarean delivery where risk also was increased 1.5-fold with levels suggestive of insufficiency (37.5–80 nmol/l). Vitamin D deficiency was linked to indications for cesarean including a twofold increased risk of cesarean section for prolonged labour and cesarean section for fetal distress.

Conclusions Poor maternal vitamin D status was linked to approximately a twofold increased risk of as well as to specific indications for cesarean delivery.