Serum Levels of 25-Hydroxyvitamin D and Time to Natural Pregnancy

Aim: The aim of this study was to evaluate whether natural fertility is related to serum 25-hydroxyvitamin D (25-OH-vitamin D) levels. Methods: A nested case-control study was designed from a prospective cohort of pregnant women undergoing first trimester screening for aneuploidies. Cases included women seeking pregnancy for 12-24 months. Controls were the subsequent age-matched women conceiving in less than 1 year. We excluded women aged ≥40 or <18 years, those assuming supplementary products that included vitamin D before or during pregnancy, those with irregular menstrual cycles or known causes of subfertility, those conceiving through assisted reproductive techniques or requiring ovarian stimulation and those who were overweight or obese. A quantitative detection of serum 25-OH-vitamin D and patients' interview were performed. Results: Seventy-three cases and 73 matched controls were selected. The mean ± SD serum 25-OH-vitamin D was 21.2 ± 6.8 and 19.7 ± 7.3 ng/ml, respectively (p = 0.16). The number (%) of women with serum levels <20 ng/ml (vitamin D insufficiency) was 34 (47%) and 37 (51%), respectively (p = 0.73). The adjusted OR of longer time to pregnancy in women with vitamin D insufficiency was 0.84 (95% CI 0.42-1.66). Conclusions: Our study does not support a crucial role of 25-OH-vitamin D in natural fertility.