Does swallowing semen make you fertile? Here's what research says

Scientists at Leiden University Medical Centre, a respected college hospital in the Netherlands, gathered a relatively small sample of 97 women under age 36 with at least three unexplained consecutive miscarriages before 20 weeks of gestation with the same partner. They also had a matched control group of 137 women who had not experienced any complications with their pregnancy. All of the women were asked to fill out a questionnaire looking into their demographics, sexual behavior, health, and lifestyle.

Reporting in the Journal of Reproductive Immunology, they found that 41 out of 72 women (56.9 percent) who experience recurrent miscarriage reported having oral sex with the partner, compared to 70 out of 96 (72.9 percent) of the matched controls. In other words, those who experienced recurrent miscarriage were less likely to have oral sex.

So, what explains this trend?

The research did not look for an underlying mechanism or causal link to explain their results, so it’s important to remember the golden rule: correlation does not imply causation. The link does not automatically mean that one factor is the sole and direct cause of change in the result. It's possible that a number of intertwined factors, such as age or social background, could also be toying with the results in a complex and fiddly way.

Nevertheless, the team delved into other scientific studies and found evidence to suggest that the link here could be to do with the immune system of the mother. Previous studies have linked the role of the immune system during pregnancy and recurrent miscarriage, with some even suggesting an immune response to the fetus could explain a significant number of unexplained miscarriages. The researchers put forward the idea that oral sex exposes the mother to paternal antigens in the partner’s semen. This helps them to build a tolerance to the antigens, such as human leukocyte antigens (HLA), making a strong immune response to the fetus less likely.

“This study suggests a possible protective role of oral sex in the occurrence of recurrent miscarriage in a proportion of the cases,” the study authors write.

“This is in line with the hypothesis that the gut has the most adequate absorption in the absence of an inflammatory environment, and seminal fluid contains soluble HLA antigens which can already induce maternal immune tolerance towards inherited paternal antigens of the fetus before implantation."

The researchers acknowledge that their sample group is small, and did not provide evidence that swallowing semen actually leads to a lower miscarriage rate. And, of course, they are not suggesting whether or not you and your partner should partake in oral sex, either. But they think their results are strong enough to link the two and warrants further study.