Oral sex is associated with reduced incidence of recurrent miscarriage.

• At population level, women with unexplained recurrent miscarriage had less oral sex. • Oral sex seems to influence pregnancy outcome in a proportion of the women. • Oral sex might induce maternal tolerance towards paternal antigens of the fetus. A possible way of immunomodulation of the maternal immune system before pregnancy would be exposure to paternal antigens via seminal fluid to oral mucosa. We hypothesized that women with recurrent miscarriage have had less oral sex compared to women with uneventful pregnancy. In a matched case control study, 97 women with at least three unexplained consecutive miscarriages prior to the 20th week of gestation with the same partner were included. Cases were younger than 36 years at time of the third miscarriage. The control group included 137 matched women with an uneventful pregnancy. The association between oral sex and recurrent miscarriage was assessed with conditional logistic regression, odds ratios (ORs) were estimated. Missing data were imputed using Imputation by Chained Equations. In the matched analysis, 41 out of 72 women with recurrent miscarriage had have oral sex, whereas 70 out of 96 matched controls answered positive to this question (56.9% vs. 72.9%, OR 0.50 95%CI 0.25−0.97, p = 0.04). After imputation of missing exposure data (51.7%), the association became weaker (OR 0.67, 95%CI 0.36–1.24, p = 0.21). In conclusion, this study suggests a possible protective role of oral sex in the occurrence of recurrent miscarriage in a proportion of the cases. Future studies in women with recurrent miscarriage explained by immune abnormalities should reveal whether oral exposure to seminal plasma indeed modifies the maternal immune system, resulting in more live births. [ABSTRACT FROM AUTHOR]