Miscarriage is the most common negative outcome of pregnancy, and identification of modifiable risk factors is potentially of great importance for public health. Low vitamin D concentrations in pregnancy are widespread worldwide, and vitamin D deficiency is implicated in immune cell regulation at the feto-maternal interface and several diseases of pregnancy.
We investigated whether 25-hydroxyvitamin D serum concentration was a modifiable risk factor for early miscarriage.
In a prospective cohort study of 1683 pregnant women donating serum before gestational week 22, we investigated the association between maternal serum concentrations of serum 25-hydroxyvitamin D [25(OH)D] and the risk of subsequent miscarriage (n = 58).
The adjusted hazard of first-trimester miscarriage was lower with higher 25(OH)D concentrations (HR: 0.98; 95% CI: 0.96, 0.99). Concentrations of 25(OH)D 2-fold increased adjusted HR for miscarriage (HR: 2.50; 95% CI: 1.10, 5.69). Concentrations of 25(OH)D were not associated with an increased risk of second-trimester miscarriage.
We found an association between 25(OH)D and first-trimester miscarriages, suggesting vitamin D as a modifiable risk factor for miscarriage. To test this hypothesis, randomized controlled trials should investigate the possible effect of vitamin D supplementation to increase 25(OH)D concentrations in early pregnancy, or before conception, to decrease risk of miscarriage. This trial was registered at clinicaltrials.gov as NCT02434900.