Association between maternal

study questionWhat are the roles of maternal 5,10-methylenetetrahydrofolate reductase ( SUMMARY ANSWER: Our study reveals for the first time that the oocyte maturation potential gradually decreases with a reduction of maternal MTHFR activity determined by combined C677T/A1298C polymorphisms, while embryo quality was worse in women with intermediate MTHFR activity. WHAT IS KNOWN ALREADY: Although many previous studies have explored the association between STUDY DESIGN SIZE DURATION: This is a retrospective cohort study investigating 1160 women who were referred for PARTICIPANTS/MATERIALS SETTING

methodsWomen who were referred for MAIN RESULTS AND THE ROLE OF CHANCE: Women with the combined 677TT/1298AA genotype (hereafter abbreviated as TT/AA, as with other combined genotypes), whose enzyme activity was the lowest, had a lower oocyte maturation rate compared with those with the wild-type genotype ( LIMITATIONS REASONS FOR CAUTION: Our study population had comparable embryological outcomes but worse clinical outcomes than other women undergoing IVF/ICSI treatment at our hospital. Therefore, the results related to the clinical outcomes should be generalized with caution. In addition, we did not detect the folate concentration of each patient during pregnancy. However, this might not have much influence on our results because almost all of our study participants took sufficient folic acid around pregnancy. WIDER IMPLICATIONS OF THE

findingsWe provide a holistic view of the effect of STUDY FUNDING/COMPETING INTERESTS: This work was funded by the National Natural Science Foundation of China (31871447, and 82101677), the National Key Research and Development Program (2019YFA0801400) and the Natural Science Foundation of Beijing Municipality (7202226). The authors declare that they have no competing interests. TRIAL REGISTRATION NUMBER: N/A.