Association between vitamin B12 and pregnancy outcomes with the follicular-phase GnRH agonist protocol: a single-center retrospective cohort study

Background Vitamin B12 takes essential effects on human reproductive system. The impact of Vitamin B12 on the outcome of assisted reproduction technology (ART) still remains elusive. This study was aimed to investigate whether vitamin B12levels is associated with the outcomes of IVF-ET. Methods A retrospective study was carried out in an assisted reproduction unit in a Chinese teaching hospital, from November 2018 to December 2019. A total of 356 infertile women, aged 20–45 years, were included. The patients were classified by vitamin B12 status: deficient (B12 350 pg/ml). Linear regression and smooth curve fitting were performed to analyze the association between Vitamin B12 and the outcomes of IVF-ET. Result(s) We found a nonlinear relationship and threshold effect between serum vitamin B12 and the outcomes of IVF-ET, after adjusting for various potential confounding factors. When the vitamin B12 value is lower than 357.1 pg/ml, the vitamin B12 is significantly positively related to the clinical pregnancy outcomes, each 10 pg/ml increase in the vitamin B12 value, the clinical pregnancy rate increased by 4% (OR=1.04, 95% CI=1.00, 1.09, P=0.0337), When the vitamin B12 value is greater than 357.1 pg/ml, the vitamin B12 is not significantly related to the clinical pregnancy outcomes (P>0.0337). Conclusion(s) Lower serum vitamin B12 levels are associated with a lower clinical pregnancy rate in IVF, for the normal and deficient vitamin B12 Chinese infertile women who undergo IVF-ET with the follicular-phase GnRH agonist protocol.