Timing is everything, right? Not so fast. Two new studies suggest that having sex at any time may boost a woman's chances for getting pregnant, even if it's outside of the ovulation cycle.

The studies, based on data collected from 30 women who participated in the Kinsey Institute's Women, Immunity and Sexual Health (WISH) Study were both led by Tierney Lorenz, a visiting research scientist at the Kinsey Institute of Research in Sex, Gender and Reproduction at Indiana University at Bloomington, in the United States of America.

"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," Lorenz said in a press release.

"This research is the first to show that the sexual activity may cause the body to promote types of immunity that support conception", he added.

In the paper published in Fertility and Sterility, Lorenz and colleagues collected saliva samples from 30 healthy premenopausal women, 16 of which were abstaining from sex – and 14 who were sexually active – at the four phases of the women's cycle: menstrual, follicular, ovulatory and luteal phases. 

Lorenz and colleagues found significantly higher levels of type 2 helper T cells, which are believed to help the body accept changes associated with pregnancy, during the luteal phase of the menstrual cycle.

They also found higher levels of type 1 helper T cells, which act as the body's defense against illness or disease, in the same women during the follicular phase of the menstrual cycle.

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

In the paper published in Physiology and Behavior, Lorenz and colleagues collected the same type of saliva samples from 32 healthy premenopausal women – 15 sexually active and 17 abstinent.

Once again, the sexually active women showed greater changes to helper T cells and proteins that T cells use to communicate to the body that it's ready for pregnancy.