A new study has found that impending fatherhood can lower two hormones — testosterone and estradiol — in men, even before their babies are born.
According to researchers at the University of Michigan, previous studies have shown that men’s hormones change once they become fathers. The new study is the first, they claim, to show that the change may begin even earlier, during the transition to fatherhood, said Dr. Robin Edelstein, the study’s lead author.
“We don’t yet know exactly why men’s hormones are changing,” said Edelstein, an associate professor of psychology. “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.”
Whatever the cause of the changes, she notes that these hormonal changes could have “important implications for paternal behavior once their babies are born.”
For the study, Edelstein and her research team 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.
The researchers found that women showed large prenatal increases in all four hormones, while men saw declines in testosterone — associated with aggression and parental care — and estradiol, which is linked to 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.
One limitation of the new study, especially as it relates to lower testosterone, is that researchers did not have a comparison group of men who are not expecting a child.
“Thus, we can’t completely rule out the possibility that the changes are simply due to age or the passage of time,” Edelstein said.
The study was published in the American Journal of Human Biology.
Source: University of Michigan