Vitamin D level is associated with increased clinical pregnancy rate and live birth rate in Chinese women undergoing IVF/ICSI-ET: a retrospective cohort study

Research question To explore the relationship between serum 25(OH)D level and Clinical Pregnancy Rate (CPR) as well as Live Birth Rate (LBR) in Chinese women receiving IVF/ICSI-ET. Design: The data of 612 patients who underwent IVF/ICSI-ET in the Reproduction Center of the Second Affiliated Hospital of Wenzhou Medical University were retrospectively analyzed. Results: None of the baseline characteristics of participants were significantly different between the two cohorts. The trend of 25(OH)D concentration was positively correlated with CPR and LBR. Moreover, our results indicated that the younger (Age: p <0.001 both in CPR and LBR) women with primary infertility (Infertility type: p =0.004 in LBR) were more likely to get a better pregnancy outcome under the same 25(OH)D concentration stages. As shown on heatmap plots, CPR and LBR were significantly increased for 25(OH)D concentrations above 30.00ng/ml and women younger than 30 years old. The adjusted binary logistic regression and RCS showed that there exists a nonlinear positive correlation between 25(OH)D concentration and pregnancy outcome (CPR and LBR) ( nonlinear < 0.001, respectively). The women with a sufficient 25(OH)D concentration (30ng/ml) had 1.07 (clinical pregnancy) and 1.05 (live birth) times higher successful birth outcomes compared to women with an insufficient 25(OH)D concentration (25ng/ml). (OR 25ng/ml,ref=30ng/ml [95%CI] = 0.935[0.932-0.938] and 0.947[0.945-0.950],P<0.001, respectively) Conclusion: In Chinese women receiving IVF/ICSI-ET, the serum level of 25(OH)D demonstrated a non-linear positive correlation with pregnancy outcome（CPR&LBR, with stronger correlations above 25 ng/ml and worse yields below 30 ng/ml. However, it could not yet be considered different in distinct ages.