Doctors already know stress is tied to increased risk of heart disease and conditions like depression, but now, new research suggests stress may be a reason women trying to conceive experience difficulty getting pregnant.

The researchers, led by Dr. Courtney Denning-Johnson Lynch, director of reproductive epidemiology at Ohio State University Wexner Medical Center in Columbus, report their findings in the journal Human Reproduction.

The new study builds on the team’s earlier work – that found a link between high levels of stress and reduced likelihood of pregnancy – by finding it is also tied to increased risk of infertility.

For the new findings, the team examined data on 501 couples trying to conceive who were enrolled in the Longitudinal Investigation of Fertility and the Environment (LIFE) Study between 2005 and 2009 at two research centers in the US, one in Michigan and the other in Texas.

The couples were followed for up to 12 months as they tried to conceive.

As part of the data collection, the female participants, aged between 18 and 40, and free from fertility problems, gave saliva samples the morning after they were enrolled and also the morning after their first period after enrollment. From these samples, the researchers could measure levels of cortisol and alpha-amylase, known biomarkers of stress.

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Women with the highest levels of a known biomarker of stress had a 29% lower chance of becoming pregnant, researchers found.

Over the 12 months of the study period, of the 401 women who completed it, 347 (87%) became pregnant and 54 (13%) did not.

When they analyzed the data, the researchers found the women with the highest levels of alpha-amylase had a 29% lower chance of becoming pregnant each month, compared with women with the lowest levels.

Also, the women with the highest indicated stress levels were more than twice as likely to meet the clinical definition of infertility, which is not conceiving despite 12 months of regular, unprotected intercourse.

These links remained despite adjusting for possible factors like age, race, income and use of alcohol, caffeine and tobacco while trying to conceive.

Dr. Lynch, who is the principal investigator of the psychological stress part of the LIFE Study, says this is the second time they have shown women with high levels of the stress biomarker alpha-amylase are less likely to become pregnant, compared with women with low levels, and adds:

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.”

She says she hopes the findings will persuade women finding it difficult to conceive to look for ways to reduce their stress with methods such as meditation, yoga and mindfulness stress reduction.

But she also notes that couples should not blame themselves if they cannot conceive, because stress is only one of several potential reasons.

Funds from the Eunice Kennedy Shriver NICHD helped finance the study.

In July 2013, Medical News Today reported a study that found shift work is linked to reduced fertility. After re-analyzing data on the effect of shift work on health, researchers found women who worked shifts were more likely to suffer disrupted menstrual periods and experienced a higher rate of miscarriage.