Pregnant woman

So you're pregnant, and you partner has become a little emotional, maybe a tetch moody and getting a little, shall we say, plump?

Turns out it might not be sympathy weight gain or the rare Couvade syndrome which causes men to have a phantom pregnancy alongside their partner (like this poor bloke in Manchester who described his condition as "I’ve never felt so rough.").

A new study from The American Journal of Human Biology has found that just as women’s hormones fluctuate (wildly) in pregnancy, so too can their partner’s as the pregnancy progresses.

"There are hormonal changes going on with men as well, and they occur earlier than other studies have suggested," the study’s lead researcher Robin Edelstein, an associate professor of psychology at the University of Michigan, Ann Arbor said.

“What we found is there is a gradual decline in men's testosterone."

The study followed 29 couples who were pregnant with their first child and over the course of the pregnancies checked in with each couples levels of salivary testosterone, cortisol, estradiol and progesterone four times.

While all four hormones increased in women. (Women's testosterone declines after birth.) the men showed declines in levels of both testosterone and estradiol, their levels of cortisol or progesterone remained the same.

So far the researchers don’t yet know what causes the lowering of testosterone but are keen to explore it. While the decline in the level of testosterone was small and not enough for the men to be considered low-testosterone, the researchers have speculated that the –very slight 'softening'- might have something to do with preparing to become a father and care-giver.