Although doctors and researchers have long suspected that there is a relationship between stress and the likelihood that a woman becomes pregnant, until now they had no scientific evidence to prove it. Now, that link has finally been empirically demonstrated, the Los Angeles Times writes. Women who are stressed out, researchers found, are indeed less likely to become pregnant.

The authors of the new study kept tabs on 400 female volunteers who were just beginning to try for a pregnancy. Over the four years, the researchers found that women who had the highest levels of a stress indicator called alpha-amylase in thier saliva were 30 percent less likely to become pregnant than women who were significantly less stressed out, the LA Times reports. But that's not the end of the story:

The researchers still do not understand exactly why stress affects a woman's ability to become pregnant, but this study did rule out some possibilities. For example, they found women with high levels of alpha-amylase had the same amount of sex as some of their less-stressed counterparts. They also found no correlation between high levels of alpha-amylase and ovulation problems. One theory the researchers plan to explore in future studies is whether stress changes what [reproductive epidemiologist Courtney Denning-Johnson] Lynch called "the hormonal milieu" of the uterus in such a way that it becomes inhospitable to implantation. "But that's still a big question mark," she said.

As the researchers pointed out to the LA Times, it's not that stressed women are doing something wrong or should feel guilty. Instead, the LA Times continues, they should view these findings as an opportunity to try to change their circumstances—including eliminating whatever it is that is stressing them out or finding ways to better manage that stress. As Lynch told The New York Times, “Yoga, meditation and mindfulness have been successful in other health outcomes and might be helpful for fertility as well.”