By Lisa Rapaport

Men may be more likely to experience fertility problems if their mothers endured stressful life events early in pregnancy, a recent study suggests.

Compared to men with mothers who had stress-free early pregnancies, men whose mothers experienced one or more stressful life experiences were more likely to have lower testosterone, lower total sperm count, and sperm less able to move through the female reproductive tract to reach an egg.

For the study, researchers looked data on reproductive hormones and sperm quality and quantity for 643 men at age 20.

Overall, 407 men, or 63%, had mothers who lived through at least one stressful life event early in pregnancy, like the death of a close relative or friend, separation or divorce, marital problems, job loss, money problems, pregnancy complications, or a residential move. Mothers of 87 men had endured at least three stressful life experiences early in pregnancy.

Mothers who reported no stressful life experiences early in pregnancy were more likely to be affluent and a healthy weight.

Pregnancy normally lasts about 40 weeks, and babies born after 37 weeks of gestation are considered full-term. Researchers asked women about any stressful life experiences they had gone through in the previous four weeks at two points in pregnancy: 18 and 34 weeks gestation.

Stressful life experiences later in pregnancy weren’t clearly associated with sons’ fertility in adulthood.

“The health of the couple at the time of conception, and for the woman her health during pregnancy, has a significant impact on the health of the offspring after birth, through childhood and into adulthood,” said Dr. Roger Hart, senior author of the study and a fertility researcher at the University of Western Australia.

“For a couple planning a family … the best time to try to attempt to conceive is when both the female and the male partner are as healthy as possible, both with respect to their physical and mental health,” Hart said by email.

The biological connection between early pregnancy exposure to stressful life experiences and male infertility isn’t well understood, Hart and colleagues note in Human Reproduction. But weeks 8 to 14 of pregnancy are a critical period for male reproductive development, the study team notes, and it’s possible stress exposure during this time might interrupt the normal development process.

The study wasn’t a controlled experiment designed to prove whether or how any stress mothers experienced during pregnancy might directly impact their sons’ reproductive health decades later. And the researchers didn’t track the men to see who went on to father children.

Another limitation of the study is that not all people respond the same way to the same stressors, and researchers lacked data on how women felt about certain experiences that the study team classified as stressful life experiences.

Factors like socioeconomic status, maternal education, and lack of insurance could all impact how women cope with stressful experiences.

Still, the results add to the evidence suggesting that it’s important to manage stress during pregnancy, said Dr. Muhammad Imran Omar, a researcher at the University of Aberdeen in the U.K. who wasn’t involved in the study.

“Stressful life events are associated with physiological, metabolic and hormonal changes in the body,” Omar said by email.

“These changes also occur during pregnancy and can impact the development of the fetus,” Omar added. “Stressful life events are associated with a high level of stress hormone cortisol in the body, and these high levels are also found in the amniotic fluid and can affect fetal development.”

SOURCE: Human Reproduction, online May 31, 2019.