Women who are under considerable stress may find it more difficult to conceive, according to a new study. The findings, however, did not apply to men.

Living a modern, fast-paced lifestyle is taking its toll on Americans. According to a 2017 Gallup poll, about eight in ten Americans say they frequently (44%) or sometimes (35%) encounter stress in their daily lives. Women are more likely to report frequent stress than men (49% vs 40%), which can trigger anxiety and depression.

Researchers at the Boston University School of Medicine investigated whether there was any association between stress and the odds of conception for women among the general population. To this aim, they turned to the Pregnancy Study Online (PRESTO), a preconception cohort that followed couples for 12 months or until pregnancy, whichever came first.

PRESTO included 4,769 women and 1,272 men who had no prior history of infertility and had not been trying to conceive for more than six menstrual cycles.

The researchers measured perceived stress among the participants by employing a 10-item test designed to assess how unpredictable and overwhelming individuals find their life circumstances. Each item referred to the past month and had five response choices, ranging from 0 (never) to 4 (very often). Both partners had to complete the perceived stress scale (PSS), whose maximum score is 40, indicating severe daily stress.

Besides PSS, the researchers also assessed data on diet, sleep, household income, frequency of intercorse, and demographic factors such as race or ethnicity.

On average, the baseline perceived stress score was about 1 point higher among women than in men, in line previous surveys and studies. The study’s most important finding, however, was that women who scored 25 or higher on the PSS were 13% less likely to conceive than women with PSS scores under 10. This association was stronger among women who had been trying to conceive for no more than two menstrual cycles and were under 35 years old.

The researchers note that only a small proportion of this association can be explained by less frequent intercourse and increased menstrual cycle irregularity due to stress.

Another important finding was that the PSS score did not seem to influence a man’s odds of conception. If there’s really a causal relationship, perhaps stress may interfere with a woman’s hormonal balance in such a way as to interfere with conception.

The authors have proposed several biological mechanisms through which stress might directly affect a woman’s fecundability. For instance, stress is known to be associated with higher levels of corticotropin-releasing hormones and glucocorticoids, which could delay or inhibit the surge of luteinizing hormones directly involved in ovulation induction. Stress might also reduce ovarian reserves.

More research will be required in order to establish such a causal link. In the meantime, couples who find it hard having a baby might want to consider managing their stress.

The findings appeared in the American Journal of Epidemiology.