Pregnant women have to deal with a lot: nine months of morning sickness and pregnancy brain and swollen feet and stretch marks, followed by giving birth. So it might seem like expectant dads get off easy.
And while guys don't have to grow a human or anything, recent research suggests that pregnancy affects their bodies too. In a new study of 29 couples expecting a first child, researchers used saliva tests to measure hormone levels of both expectant parents up to four times throughout the pregnancy.
Levels of the sex hormones estradiol and testosterone declined among the men throughout the nine months. While experts already knew that testosterone levels dip after men have children, the new data shows these changes happen even before the baby is born.
Researchers can't fully explain the phenomena. What they do know: Lower levels of testosterone make men more nurturing, caring, and loyal, according to Rachel Edelstein, Ph.D., a psychologist and director of the Personality, Relationships, and Hormones Lab at the University of Michigan. This, at least in theory, makes them better fathers and partners. While more research is needed, estradiol likely has the same effects, Edelstein says.
Interestingly, couples in the study also had similar levels of progesterone and cortisol—they were generally high or low in both expectant parents. Because these hormones are linked to stress, the correlation suggests that moms- and dads-to-be are definitely on the same page.
This article orginally appeared on Cosmopolitan.com. Minor edits have been made by the Cosmo.ph editors.