Background: Recent studies suggest that vitamin D may play a role in human reproduction. Our goal was to investigate whether vitamin D levels are predictive of implantation and clinical pregnancy rates in infertile women following in vitro fertilization (IVF).
Methods: We prospectively evaluated vitamin D status, as determined by serum 25-hydroxy-vitamin D (25[OH]D) levels, in a cohort of 173 women undergoing IVF at Mount Sinai Hospital, Toronto, Ontario. Serum 25(OH)D samples were collected within 1 week before oocyte retrieval. We classified patients as having sufficient (≥ 75 nmol/L) or insufficient (or deficient; hereafter referred to as "insufficient"; < 75 nmol/L) serum levels of 25(OH)D. We compared patient demographics and IVF cycle parameters between groups. The primary outcome measure was clinical pregnancy (intrauterine sac visible on ultrasound performed 4-5 weeks after embryo transfer).
Results: Of the included women, 54.9% had insufficient 25(OH)D levels and 45.1% had sufficient levels. Women with sufficient levels had significantly higher rates of clinical pregnancy per IVF cycle started (52.5%) compared with women with insufficient levels (34.7%; p < 0.001). Implantation rates were also higher in the sufficient 25(OH)D group, but the results were not statistically significant. Multivariable logistic regression analysis (adjusted for age, body mass index and day 5 [v. day 3] embryo transfer) showed that serum 25(OH)D level may be a predictor of clinical pregnancy (adjusted odds ratio 1.01, 95% confidence interval 1.00-1.03).
Interpretation: Our findings suggest that women with sufficient levels of vitamin D are significantly more likely to achieve clinical pregnancy following IVF. Vitamin D supplementation could provide an easy and cost-effective way of improving pregnancy rates; this merits further investigation.
Trial registration: ClinicalTrials.gov, no. NCT01348594.