Courtney Denning-Johnson Lynch, director of reproductive epidemiology at Ohio State University's Columbus Wexner Medical Center in Columbus, and colleagues found women with high levels of alpha-amylase -- a biomarker of stress in saliva -- are 29 percent less likely to get pregnant each month and are more than twice as likely to meet the clinical definition of infertility, compared to women with low levels of this enzyme.
The medical definition of infertility is not being able to become pregnant despite 12 months of regular unprotected sexual intercourse.
The research team tracked 501 U.S. women ages 18 to 40, who were free from known fertility problems and had just started trying to conceive, for 12 months or until they became pregnant.
Saliva samples were collected from 373 study participants for the presence of salivary alpha-amylase and cortisol, two biomarkers of stress.
"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," Lynch said in a statement. "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."
The findings were published in the journal Human Reproduction.