Does swallowing sperm really reduce the risk of recurring miscarriage?

A new study, published in Journal of Reproductive Immunologyon March 27, suggests that woman who more frequently gave their partners oral sex, and swallowed the semen, were less likely to suffer recurring miscarriages.

Wait; what?

In the study, Dutch researchers compared the habits of 97 woman who have suffered recurrent miscarriage, defined as the loss of three or more consecutive pregnancies, to 137 women who did not. It was found that the woman who did not endure recurring miscarriages were performing markedly more oral sex on their partners than the members of the former group.

Of the women with recurring miscarriages, a little more than half reported giving oral sex. Nearly 75 percent of the other group reported doing so.

Now, this is all just correlation right now, and we all know that correlation does not prove causation. The scientists have yet to identify a mechanism that relates giving oral sex and having fewer miscarriages. It also relies entirely on self-reporting by a small number of test subjects.

At this point we don’t know if the results aren’t caused by other factors — suppose that woman who enjoy giving oral sex are just somehow inclined to have fewer miscarriages, for example. However, this study could be the basis for further investigation into the issue that does find something more tangible.

The authors of the study have speculated on what that mechanism might be. One idea is that exposure to the genetic material of their partners might be giving their immune system time to recognize it and reduce the chance it will see a fetus as foreign if it includes the same DNA. As they mentioned in their study, this notion isn’t without precedent:

“A well-known route to induce immune tolerance is via oral exposure, possibly because the gut has the most adequate absorption in the absence of an inflammatory environment. In transplantation models of rats, oral administration of MHC molecules diminishes the occurrence of allograft rejection. In addition, Clark et al showed that direct seminal plasma antigen presentation to a mouse model of NK-cell mediated recurrent miscarriage may prevent the rejection of embryos. Koelman et al hypothesized that a potent way of inducing tolerance towards paternal HLA antigens of the fetus in pregnancy would be exposure of these antigens to oral mucosa. To support this theory, they showed that both oral sex and swallowing sperm reduced the incidence of preeclampsia.”

The above excerpt references several other studies, including one that showed a connection between swallowing semen and a reduced rate of preeclampsia in expecting mothers.

The researchers conclude, “[Oral] exposure to seminal fluid seems to induce maternal tolerance to paternal antigens and therefore influence pregnancy outcome in a positive way.”

The maternal immune system

Strange as it is to think, in a way a fetus is like a foreign object in the mother’s body which the immune system would have an interest in. While the womb is supposed to be an immunologically privileged area, some studies have suggested that unexplainable miscarriages could be caused by an immune response to the fetus. RH disease and preeclampsia are examples of less severe reactions to an improper immune response.

While the idea of more oral sex as a practical solution to the problem of recurring miscarriage will undoubtedly interest quite a few people, the jury is still out.