Introduction: Low 25-hydroxyvitamin D (25OHD) levels are frequently found in fertile women and associated with low birth weight, reduced fertility and adverse pregnancy outcomes.
Objective: We investigated the effects of vitamin D supplementation on birth weight, fertility, and delivery complications in women planning pregnancy with low 25OHD levels.
Methods: This was an investigator-initiated double-blind, randomized, placebo-controlled, parallel-group trial from a single centre.
Patients: A total of 193 women planning pregnancy (2040 y old) with 25OHD level below 50 nmol/l were recruited.
Interventions: Daily supplementation of cholecalciferol 70 μg (2800 IU) (70-VitD3), 35 μg (1400 IU) (35-VitD3) or matching placebo was administered before conceiving and continued until 16 weeks post partum.
Main outcome measures: 25OHD, birth weight, fertility, and complication were evaluated.
Results: Baseline level of 25OHD did not differ between groups (mean 43 nmol/l; P=0.91). Levels of 25OHD increased dose-dependently in response to treatment (P<0.001). A total of 108 women (56%) conceived within 12 months after randomization, 41 (38%) in the placebo group, 31 (29%) in the 70-VitD3, and 36 (33%) in the 35-VitD3 group. Compared with placebo, the 35-VitD3 group did not affect pregnancy chances significantly (HR: 0.79; 95% CI: 0.48, 1.28), but chances of conceiving were significantly reduced by a daily supplement of 70 μg (HR: 0.52; 95% CI: 0.31, 0.87). Birth weight did not differ significantly between the vitamin D3 treated and the placebo group. Complications during labour were significantly more frequent in the placebo- compared with the combined vitamin D3 group (52 vs 23%, P< 0.005), although specific complications did not differ between groups. There were no differences between groups on any safety measures.
Conclusions: High doses of vitamin D3 (70 μg/daily) may reduce the likelihood of conceiving, but may also be associated with fewer complications during childbirth without affecting birth weight.
Approved by The Ethical Committee of Denmark (M-20090097).
14 May 2016 - 17 May 2016