Context: Vitamin D deficiency has been proven to affect fertility in mammals, but data in human is less convincing. In particular, data on in vitro fertilization (IVF), an attractive model to draw information on this topic, are sparse and conflicting.
Objective: Our objective was to investigate IVF outcome in women with deficient 25-hydroxy-vitamin D [25(OH)D] serum levels (<20 ng/mL).
Design and setting: This prospective cross-sectional study was conducted at the infertility unit of an academic setting.
Patients: The main inclusion criteria were as follows: (1) indication to IVF, (2) age 18-42 years, (3) BMI 18-25 kg/m(2), (4) adequate ovarian reserve according to Bologna criteria. Eligible women provided a serum sample for 25(OH)D measurement at the time of cycle preparation. Subjects were subsequently excluded if the cycle was cancelled or if the attempt was excessively delayed.
Intervention: Quantitative detection of serum 25(OH)D.
Main outcome measure: Clinical pregnancy rate.
Results: The number of recruited women with serum 25(OH)D <20 ng/mL and ≥ 20 ng/mL was 154 and 181, respectively. The clinical pregnancy rates were 20% (30/154) and 31% (56/181), respectively (P = .02); the adjusted odds ratio for clinical pregnancy in women with vitamin D ≥ 20 ng/mL was 2.15 (95% CI: 1.23-3.77). Subgroup analyses showed that the group of women with the highest serum levels (>30 ng/mL) had the highest chances of pregnancy.
Conclusions: Vitamin D is an emerging factor influencing female fertility and IVF outcome. Additional studies are pressingly needed to confirm a causal relationship and to investigate the potential therapeutic benefits of vitamin D supplementation.