Having sex alters immune system so you’re more likely to get pregnant

If you’re struggling to conceive—or if you don’t want to just yet—a new study out of the Indiana University Bloomington has some important news for you: Having frequent sex appears to alter the female immune system, improving chances of conceiving—even outside of ovulation.

“It’s a common recommendation that partners trying to have a baby should engage in regular intercourse to increase the woman’s changes of getting pregnant—even during so-called ‘non-fertile’ periods— although it’s unclear how this works,” said Tierney Lorenz, lead author of two new papers on the subject and visiting research scientist at the Kinsey Institute, in a statement. “This research is the first to show that the sexual activity may cause the body to promote types of immunity that support conception.

“It’s a new answer to an old riddle: How does sex that doesn’t happen during the fertile window still improve fertility?”

Previous studies have shown that the immune system alters its function during pregnancy, at various stages in the menstrual cycle, and following childbirth, but these studies are the first to show that sex also can make key changes in immune regulation.

Immune changes

The data for both papers came from participants in the Kinsey Institute’s WISH Study (Women, Immunity and Sexual Health). The Institute collected information about 30 women—roughly half sexually active and half not—for the full span of their menstrual cycles.

The first of the papers, published in Fertility and Sterility, discovered that the sexually active women demonstrated a great change in immune system components known as helper T cells, along with the proteins that support them. The second paper, which can be found in Physiology and Behavior, found key differences in antibody levels between the two groups of women.

Helper T cells are responsible for recognizing threats to the body and activating other immune cells to combat them, and there are two general kinds. Type 1 focuses on augmenting the body’s defense systems against foreign threats. Meanwhile, type 2 helps the body in accepting what may be seen as foreign invaders, like sperm or an emerging embryo.

The antibodies (also called immunoglobulins) are created by white blood cells, and also work to fight off foreign invaders. There are many kinds of immunoglobulins, but the study focused on immunoglobulins A (IgA) and G (IgG). IgA is usually found in the mucous of the female reproductive tract, and can interfere with fertilization; IgG is usually found in the blood and fight off invaders without interfering with the uterus.

A careful balance

“The female body needs to navigate a tricky dilemma,” Lorenz said. “In order to protect itself, the body needs to defend against foreign invaders. But if it applies that logic to sperm or a fetus, then pregnancy can’t occur. The shifts in immunity that women experience may be a response to this problem.”

For the sexually active women, they detected significantly higher levels of type 2 helper T cells and IgG—the immune system components that aid in accepting certain aspects needed for pregnancy and for regulating the immune system outside of the uterus—during the phase of the menstrual cycle in which the uterine lining thickens in preparation for pregnancy and which follows ovulation.

During the phase in which the ovaries’ follicles are maturing, which happens right after menstruation, the sexually active women showed higher levels of type 1 helper T cells and IgA.

The sexually abstinent women, however, showed none of these changes.

“We’re actually seeing the immune system responding to a social behavior: sexual activity,” Lorenz explained. “The sexually active women’s immune systems were preparing in advance to the mere possibility of pregnancy.”

—–

Feature Image: Thinkstock