Women exposed to stress in pregnancy ‘have sons with lower sperm count’

Men born to mothers who experienced stress in early pregnancy may have reduced sperm counts as adults, new research suggests.

Women who went through a challenging life event – such as the death of a relative – in the first 18 weeks of gestation also had sons with fewer sperm that could swim well, according to the study in journal Human Reproduction.

The researchers suggest the early stages of pregnancy are an important time for developing male reproductive organs, and said exposure to stress during this period may have long-term consequences for fertility.

Professor Roger Hart, senior author of the study from the University of Western Australia, said maternal stress is unlikely to cause infertility in male offspring on its own, but could be a contributing factor.

The scientists studied 643 men aged 20 years old, whose mothers were monitored during their pregnancy for stressful life events including family deaths, relationship problems and money troubles.

Almost two-thirds (63%) had been exposed to at least one stressful life event in the first 18 weeks of pregnancy, while 13.5% had experienced three or more.

Men who had been exposed to three or more stressful life events had, on average, a 36% reduction in their sperm count, a 12% reduction in sperm motility and an 11% reduction in testosterone levels, compared to men who were not exposed to any stressful event during that early period, the researchers found.

“This suggests that maternal exposure to stressful life events during early pregnancy, a vulnerable period for the development of male reproductive organs, may have important life-long adverse effects on men’s fertility,” Prof Hart said.

“This contrasts with the absence of any significant effect of exposure to maternal stressful life events in late gestation.”

The researchers note that the study is observational, and does not show that maternal stress causes changes to sperm count, quality or testosterone levels.

Prof Hart said: “Like most things in life, if exposure to stressful life events in early gestation is added to other things that are known to affect men’s fertility, it may contribute to an increased risk of male infertility.

“These other, predominantly lifestyle exposures include being overweight, central obesity, smoking, excessive alcohol intake, high blood pressure, high cholesterol, sugar, or fat levels in the blood, a varicocele in the scrotum, or possibly exposure to chemicals in the environment that interfere with natural hormones, both before birth and in adulthood.”

Commenting on the findings, Dr Jane Stewart, chairwoman of the British Fertility Society, said: “There is accruing evidence of the effects of intrauterine life on adult health.

“This association of stressful events and male reproductive function may be a further piece of evidence.

“That said, the study does not confirm a causative relationship. As the authors quite correctly point out there are several potential confounding factors. These include how each of the mothers may have responded to stressors.”