Microsomal epoxide hydrolase polymorphism and risk of spontaneous abortion

We conducted a nested case-control study to examine the association of microsomal epoxide hydrolase polymorphism with spontaneous abortion. The analysis included 127 cases and 107 controls from a rural community in China. The prevalence of the homozygous wild-type (AA), the heterozygous variant (Aa), and the homozygous variant (aa) in exon 3 of epoxide hydrolase was 13.4%, 34.6%, and 52.0% in cases and 27.1%, 30.8%, and 42.1% in controls, respectively. In contrast, the variant genotypes in exon 4 of epoxide hydrolase were less frequent in cases than controls. Using women with genotype AA as the referent, the adjusted odds ratio of spontaneous abortion was 2.69 [95% confidence interval (CI) = 1.33-5.42] for those with genotype Aa or aa in exon 3; but it was 0.45 (95% CI = 0.22-0.94) for those with genotype Aa or aa in exon 4, indicating that the two variants have opposite associations with spontaneous abortion. The findings persisted after adjustment for age, education, parity, smoking, alcohol use, occupation, and pesticide exposure, as well as in subgroup analysis. Moreover, for the variant genotypes Aa or aa in exon 3, the odds ratio was twice as great in those cases with three or more spontaneous abortions than in those with fewer spontaneous abortions.