Women with higher levels of a marker of stress in their saliva took longer to get pregnant and were more likely to have trouble with infertility, according to new research.
A previous study in the UK by the same authors reported similar findings on women's time to become pregnant. But it was too short to examine an association with infertility, defined as the inability to get pregnant after a full year of trying to conceive without contraception.
"In that paper we show that women who have the highest levels of salivary alpha-amylase, the stress biomarker, were 15 percent less likely to get pregnant," Courtney Lynch told Reuters Health.
Lynch, from The Ohio State University in Columbus, led the new study that was published in Human Reproduction.
This time she and her colleagues followed a larger group of U.S. women for a full 12 months and were able to look at infertility as well as time to become pregnant.
They studied 401 couples from Michigan and Texas who were trying to conceive between 2005 and 2009.
The women were asked to collect two saliva samples, one at the beginning of the study and a second sample the morning of their first menstrual period after they were enrolled.
A total of 373 women became pregnant during the study.
The researchers divided the women into three groups based on their levels of two stress markers, alpha-amylase and cortisol.
Women with the highest levels of alpha-amylase were 29 percent less likely to get pregnant than women with the lowest levels.
That translated into a doubling in their chances of meeting the cut-off for infertility, compared to women in both the middle and lowest alpha-amylase groups.
The researchers didn't find any association between cortisol and infertility.
Lynch said women shouldn't feel like it's their fault if they haven't been able to get pregnant. Stress is just a minor factor affecting a couple's ability to conceive and there are many medical issues that could also be responsible.
"If you've been trying to get pregnant longer than 12 months you need to go seek a work-up from a physician," she said.
Lynch added that couples that have gotten to the six- to 12-month window of not getting pregnant should also be thinking about their lifestyles and considering partaking in some sort of stress reduction techniques.
The researchers weren't able to collect additional saliva samples that might have determined if failing to get pregnant was linked to further changes in stress levels.
"The paper itself doesn't address the mechanisms, they just say the higher the amylase, the longer the time to conception," Dr. Sarah Berga told Reuters Health.
Berga, from Wake Forest Baptist Medical Center in Winston-Salem, North Carolina, was not involved in the new study.
"It also doesn't look at what are the outcomes of the pregnancies," she said. "But it's good that it shores up this basic idea that stressful events somehow impair the reproductive system and therefore stress is an important cause of infertility."
Berga has studied some of the ways stress might lead to infertility. For instance, she said, activation of the body's stress responses can suppress messages between the brain and the ovaries and testes.
"We also know that if you address the stress you can actually see a return of ovarian function and the brain message to the ovary," she said.
Researchers are also looking at whether high cortisol levels affect estrogen, Berga added.
She is optimistic about the benefits of stress reduction for women who are trying to get pregnant, and has studied talk therapy for that purpose.
"It really would be good for people to understand not only that stress is not good for your reproduction but the more important message is that you can do pretty simple things to manage your stress and that it might have very powerful positives," she said.
Lynch is planning to look at stress relief techniques to see if they might help women become pregnant.
"Mindfulness, meditation, even yoga, have been shown to lower stress, so I think it's reasonable to presume we're going to find them to be helpful for fertility as well," Lynch said.