Research finds that women with higher stress levels are less likely to become pregnant and more likely to be infertile, but yoga may help.

For couples having difficulty getting pregnant, stress is a common experience. But a new study shows that stress may compound the problem by reducing a woman’s ability to conceive and increasing the risk of infertility.

Exactly how stress affects a woman’s fertility is still unclear, but researchers discovered a connection between a protein stress indicator found in a women’s saliva and her chances of becoming pregnant. The study was a follow-up to previous research conducted in the U.K.

“This is now the second study in which we have demonstrated that women with high levels of the stress biomarker salivary alpha-amylase have a lower probability of becoming pregnant, compared to women with low levels of this biomarker,” said study author Courtney Denning-Johnson Lynch, director of reproductive epidemiology at the Ohio State University College of Medicine, in a press release. “For the first time, we’ve shown that this effect is potentially clinically meaningful, as it’s associated with a greater than two-fold increased risk of infertility among these women.”

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In the study, published online today in Human Reproduction, researchers measured stress levels in 373 women, ages 18 to 40, using two compounds found in saliva—alpha-amylase and the stress hormone cortisol.

Women with the highest levels of alpha-amylase, which increases in response to sudden and ongoing stress, were 29 percent less likely to become pregnant during each month of the study than women with the lowest amounts of the enzyme.

In addition, these women were more than twice as likely to be classified as infertile, which is defined as being unable to conceive after 12 months of trying without contraception.

Researchers measured each subject’s stress level at the beginning of the study and then on the morning after the start of her next menstrual cycle. The stress indicators were similar both times, but because the researchers didn’t collect samples throughout the study, they were unable to tell if stress levels changed later on. Stress may have increased as women failed to become pregnant over time.

The researchers didn’t find a connection between the amount of cortisol in the women’s saliva—a more commonly used measure of stress—and their chances of conceiving. It is not uncommon, they wrote in the paper, for changes in cortisol levels to differ from changes in alpha-amylase levels in stressed people.

Read About Tests for the Stress Hormone Cortisol »

According to the Centers for Disease Control and Prevention, about 15 percent of women ages 15 to 44 have difficulty getting pregnant or carrying a pregnancy to full term. Six percent of women in that age group are clinically infertile.

Assisted reproductive technology, such as in-vitro fertilization (IVF), has made it easier for women to become pregnant when they are faced with difficulty conceiving. But stress reduction could offer women a way to improve their chances before turning to more-expensive clinical methods.

“Stress reduction modalities, such as yoga, meditation, and mindfulness, that have been shown to be helpful in reducing stress in studies of other health outcomes, might be relevant for further consideration,” the study’s authors wrote.

This study didn’t look at whether yoga or other stress-reduction methods could improve fertility, but previous research has investigated benefits of these types of activities. This includes a 2012 study in the Journal of Alternative and Complementary Medicine, which found that just 10 days of yoga can reduce cortisol levels.

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While the authors of the study published today encourage women who are having difficulty becoming pregnant to manage their stress levels, the researchers emphasize that stress is not the only factor that affects fertility. Other issues—such as the male’s low sperm count or the woman’s ovulation problems—can also play a role.

For obese women who turn to IVF for help conceiving, their weight may be a hurdle. In another study, published last week in the Journal of Clinical Endocrinology & Metabolism, researchers at the University of Colorado Denver examined how well the bodies of obese women absorbed GnRH antagonist, a medication used during the IVF procedure.

The study found that the drug left the obese women’s blood more quickly than it left the blood of women whose weight was normal. If an IVF patient’s GnRH level drops too quickly, the brain signals ovulation sooner than expected, reducing the number of eggs doctors can collect and the chances of a successful pregnancy.

“Our findings indicate obese women may need a different or increased dosing regimen to improve fertility treatment outcomes,” said study author Dr. Nanette Santoro, in a press release. “Given the cost of IVF and stress of infertility, it is important to maximize each woman’s chances of conceiving a child.”

Learn More About In-Vitro Fertilization (IVF) »