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Email You are free to share this article under the Attribution 4.0 International license. University University of Michigan

When a couple is expecting a baby, it’s not just the mother that goes through hormonal changes. A new study suggests impending fatherhood coincides with a drop in two hormones in men—testosterone and estradiol—even before the baby is born.

Previous research has suggested that men’s hormones change once they become fathers, and there is some evidence that this is a function of a decline after the child’s birth.

The new study is the first to show that the decline may begin even earlier, during the transition to fatherhood, says Robin Edelstein, associate professor of psychology at University of Michigan.

“We don’t yet know exactly why men’s hormones are changing,” Edelstein says.

“These changes could be a function of psychological changes that men experience as they prepare to become fathers, changes in their romantic relationships, or even physical changes that men experience along with their pregnant partners.

“Nevertheless, fathers’ hormonal changes could have important implications for paternal behavior once their babies are born.”

Drop in hormones

Expectant mothers experience significant hormone changes throughout the transition to parenthood, but less has been known about the prenatal hormone changes among soon-to-be fathers.

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For the new study, published in the American Journal of Human Biology, researchers examined salivary testosterone, cortisol, estradiol, and progesterone in 29 first-time expectant couples between the ages of 18 and 45. The saliva samples were obtained up to four times during the prenatal period at about 12, 20, 28 and 36 weeks of pregnancy.

Women showed large prenatal increases in all four hormones, while men saw declines in testosterone (which is associated with aggression and parental care) and estradiol (which is associated with caregiving and bonding). No changes were found in men’s cortisol (a stress hormone) or progesterone (which is associated with social closeness and maternal behavior).

So it’s not just about the presence of an infant that lowers testosterone.

One limitation of the new study—as it relates to lower testosterone—is that researchers do not have a comparison group of men who are not expecting a child, Edelstein says.

“Thus, we can’t completely rule out the possibility that the changes are simply due to age or the passage of time.”

Source: University of Michigan