The research: Researchers from Ohio State University followed 401 women for a year. After examining blood, urine, and saliva samples, along with 12 months of daily journal entries, study author Courtney Denning-Johnson Lynch and her team discovered women with the highest levels of alpha-amylase—a biomarker of stress measured in saliva—were 29% less likely to become pregnant each month, and twice as likely to be deemed infertile after 12 months of trying. “Women have always known this to be true, and we’ve heard it anecdotally for years,” explains Lynch. “We can’t say stress causes infertility yet, but we now know there’s an association.”  What it means: Even though this is her second study on the topic, the exact relationship between stress and fertility is still a mystery. They were able to test a few hypotheses—including the belief that stressed people have less intercourse—but none panned out. At the beginning of the study, Lynch gave women a stress questionnaire and, after comparing their scores, found the population of women she was studying was actually less stressed than the overall population. “Our women’s alpha-amylase levers were not that high comparatively, which means the effect is even bigger than what our study is reporting.” Bottom line: Taking up yoga, meditation, or any other stress-relief program won’t guarantee a pregnancy, of course. But if you’ve been trying for a several months without success, experts suggest it’s a reasonable time to start paying attention to your stress levels. At the very least, it will increase your overall pre-conception health, which, according to Lynch, will put you and your overall health in a better place if you do become pregnant. More from Prevention: 2-Minute Stress Solutions