Abstract: Objective：To study the relationship between the gene polymorphism of methylene tetrahydrofolate reductase (MTHFR) and the unexplained recurrent spontaneous abortion (URSA). Methods：83 patients with unexplained recurrent spontaneous abortion (the URSA group) and 90 normal women of reproductive age (the control group) were recruited. Fluorescence quantitative PCR was used to detect the MTHFR gene C677T, A1298C single nucleotide polymorphisms (SNP). The frequency distribution of genotype and allele was compared, and  the risk of different genotypes to URSA was evaluated. Results：The distribution of MTHFR genotypes in both groups was consistent with the Hardy-Weinberg balance. There were significant differences in the frequencies of C677T genotype and alleles between the URSA group and the control group (P＜0.05). There were no significant differences in the frequencies of A1298C genotype and alleles between the two groups (P＞0.05). The frequency of homozygous genotype in the URSA group was higher than that in the control group (30.1% vs. 13.3%,  χ2=7.237,  P=0.007). The risk of URSA in those patients with TT homozygous genotype was 3.289 times higher than that in the patients with CC homozygous genotype (OR=3.289, 95%CI: 1.342-8.063). Conclusions：The gene polymorphism of MTHFR C677T site is a risk factor of URSA, and the TT homozygoous genotype increases the risk of URSA.

Key words: Abortion, habitual, 5, 10-methylenetetrahydrofolate reductase (FADH2), Polymorphism, single nucleotide, Polymerase chain reaction