Expectant mothers aren't the only family members on a hormonal roller coaster, a new study in the June issue of Mayo Clinic Proceedings shows. First-time fathers too undergo hormonal changes before and after their children are born. To explore these shifts, Sandra J. Berg and Katherine E. Wynne-Edwards of Queen's University in Ontario, Canada, recruited 23 would-be dads at first-trimester prenatal classes and another 14 men who were not fathers as controls. They took regular saliva samples from all of the men and measured levels of testosterone, cortisol (a stress hormone) and estradiola hormone known to influence maternal behavior in women, nonhuman primates and other mammals.

"Relative to control subjects, expectant fathers have lower testosterone and cortisol concentrations and more frequently detectable estradiol," Wynne-Edwards says. "These results confirm and expand on the results of the only previous study, suggesting that men's hormones change as they become fathers." Whereas the earlier study had revealed some testosterone and cortisol fluctuations in men becoming fathers, the new research was first to discover that these men were exposed to more estradioland that this exposure increased after their children were born. Now the scientists hope to learn just what these hormone changes do physiologically to new dads.