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Hormonal Pregnancy Shifts Aren't Just for Mom

If you're blaming those late-stage pregnancy mood swings on all the hormonal changes your body's going through, you may not be the only one who can play that card. According to new research in the American Journal of Human Biology, dads-to-be also go through hormonal shifts in the days and weeks leading up to baby's arrival, including dips in testosterone and estradiol levels.

The study examined 29 couples all expecting their first child, using saliva samples to measure testosterone, cortisol, estradiol and progesterone. In each case, the couples were monitored at 12, 20, 28 and 36 weeks along. While the decrease in male testosterone was significant, changes seen in other hormone levels were not.

This marks the first time that prenatal testosterone changes (or any hormone changes, for that matter) have ever been seen in dads-to-be as opposed to moms. Still, researchers note that the changes are mild in comparison to those seen in women. One other caveat is that the study did not compare these testosterone shifts to other couples who were not expecting, so it's hard to say for sure how often these shifts might occur outside of having a baby.

One other big question is why these changes even happen in the first place. Some experts have theories, based on previous research—namely that hormones have been found to change fathers after having kids, as they start to pick up more "nurturing" behaviors. A dip in testosterone has also been linked to the lack of sleep and lack of sex men often experience after having kids, which also does happen during pregnancy.

So while the facts so far have shed an interesting light on what Dad goes through in those all-too-important nine months, experts say that more research is needed to get to the bottom of what it all means.

"It will be important for future research to determine whether the changes that we observed in men’s hormones reflect processes associated with fatherhood specifically, or long-term pair-bonding more generally," the study authors wrote.

MORE: 10 Amazing Painted Pregnancy Bumps

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