Association between Vitamin D and pregnancy in women with polycystic ovary syndrome: a case-control study from Beijing, China

Abstract Background Polycystic ovary syndrome (PCOS) is the most common cause of anovulatory infertility. Several evidence show that vitamin D may be beneficial to female reproduction in PCOS. However, few studies have been done to the correlation between vitamin D levels and pregnancy in PCOS patients after ovulation induction therapy. Methods We enrolled a total of 200 newly diagnosed anovulatory infertile patients with PCOS (experimental group) and 200 healthy women of childbearing age (control group) between June 2016 and September 2018. The experiment group treated with Letrozole for inducing ovulation. We investigated the pregnancy rate for patients with PCOS and studied correlation of pregnancy rate and levels of 25-(OH) D3 in patients with PCOS. Then we evaluated serum 25-(OH) D3 levels between the two subgroups, with the experimental group divided into vitamin D-deficient and vitamin D non-deficient subgroups and analyzed their respective pregnancy rates. Results The mean serum 25-(OH) D3 level in the experimental group was significantly lower than that in the control group (14.57 ± 5.86 ng/mL vs. 22.24 ± 6.73 ng/mL, respectively; t = 12.190, P < 0.05). Of the 200 patients in the experimental group, 149 patients completed the ovulation-induction regimen, comprising 72 patients who became pregnant and 77 patients who failed to become pregnant—generating a pregnancy rate of 48.32%. We noted that the serum 25-(OH) D3 level in the pregnant patients was significantly higher than that in the non-pregnant patients (16.06 ± 5.80 ng/mL vs. 13.54 ± 5.88 ng/mL, respectively; t = 2.635, P < 0.05). Additionally, the pregnancy rate was 43.89% in the vitamin D-deficient group compared to 67.86% in the vitamin D non-deficient group, with the latter significantly higher compared to the former group (χ 2  = 5.269, P < 0.05). Conclusions Our results demonstrate that vitamin D deficiency is common in women with PCOS and vitamin D appears to play a beneficial role in PCOS patients undergoing an ovulation-induction regimen. Therefore, monitoring the serum vitamin D level in PCOS patients and timely and appropriate vitamin D supplementation are essential to improve the pregnancy success rate of infertile women with PCOS.