Yes, women are the ones who actually experience the physical act of being pregnant and the hormone changes that come with it. But a new study suggests that expecting fathers go through their own share of hormonal shifts as the due date approaches.
The study, published in the American Journal of Human Biology on Dec. 15, was the first to look at how men's hormones change along with the mother's while she's still pregnant. Researchers found that, during this prenatal period, first-time dads showed significant declines in testosterone and estradiol, a hormone associated with caregiving and bonding. Since previous studies have shown that fathers in general have lower testosterone levels than non-fathers, this hormone shift during pregnancy could be biology's way of preparing men to become dads, according to the new study.
Researchers tested the hormone levels of 29 first-time expecting couples at the twelfth week of pregnancy and then again every eight weeks until the birth. As expected, women showed large prenatal increases in testosterone, cortisol, estradiol, and progesterone. While the men experienced less of a hormonal shift in general, they did show that aforementioned drop in testosterone and estradiol.
"Having lower testosterone is good if you're around a child, because you're going to be less aggressive and it promotes nurturance," Robin Edelstein, an Associate Professor of Psychology at the University of Michigan and co-author of the study, told The Huffington Post.
Testosterone is also associated with seeking out sexual partners and dominance. Edelstein said the drop men experienced could have to do with changes in the relationship between them and their partners as well as a change in how much these men are thinking about nurturing and parenting.
Previous research has shown that estradiol may also facilitate caregiving once babies are born. So even though men in this study experienced a drop in that particular hormone during pregnancy, maybe their estradiol increased after they met their child, as previous research suggests. But again, Edelstein said that this is all speculation.
"There's a lot of evidence that these changes are happening, but less is known about why exactly," Edelstein said.
The sample in this particular study was fairly small and only included expectant fathers, so more work needs to be done to properly compare these hormonal shifts with men in non-prenatal circumstances. It's possible that these changes were experienced due to the passage of time, not pregnancy, but Edelstein said this isn't likely -- previous studies didn't find similar hormonal dips in men when pregnancy wasn't a factor.
Edelstein's findings suggest that it's important for people to understand that men may experience change during this exciting and tumultuous nine-month period, too.
"Keep in mind that this time is important for men as well," she said. "Whatever it is that men are doing while their partners are pregnant may actually be helping to prepare them to become fathers."