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Spokane, Washington  Est. May 19, 1883

She’s expecting, but him?

John Fauber Milwaukee Journal Sentinel

Your wife is pregnant; so why are you gaining weight?

Working with man’s closest relatives, researchers at the University of Wisconsin-Madison have shed new light on the centuries-old observation that is part of a phenomenon in people known as the couvade syndrome.

Also known as sympathetic pregnancy, up to 65 percent of men have been known to exhibit changes such as queasiness, headache, irritability, hormonal levels and weight gain during the pregnancy of their partners.

The big question always has been, is it biological, social or psychosomatic?

Whatever the cause, the phenomenon apparently is real, at least among expectant marmoset and tamarin fathers at the Wisconsin National Primate Research Center in Madison.

The male monkeys experienced about a 10 percent gain in weight during the five- to six-month gestation of their mates, but nonexpectant males did not gain weight. The study involved a total of 58 monkeys.

The paper is the first published report to document weight gain in expectant non-human primates. Humans are the only other species in which males are known to gain weight during the pregnancy of their mates.

An earlier study involving 81 fathers-to-be found that nearly half of them gained weight during the third trimester of their pregnant partners.

Scientists not associated with the University of Wisconsin paper, which appeared this week in the journal Biology Letters, said it is an important finding that’s likely to open up a new avenue of research into the biology of paternal care.

“It helps us understand the neurobiology and endocrinology of it,” said Joe Lonstein, a professor of psychology and neuroscience at Michigan State University. “The hope is that if this occurs in non-human primates, it occurs in humans as well.”

Most male mammals do not undergo physical changes associated with gestation, but among species in which males take part in parenting, the changes are more likely to take place, the Wisconsin researchers said.

In their paper, they say the weight gain may be the result of some evolutionary process in which males prepare for the increased energy demands of fatherhood by putting on pounds.

“It could be the weight gain is preparing men for their investment such as the sleepless nights and taking over the extra work,” said lead author Toni Ziegler, a Wisconsin endocrinologist.

In monkeys, males need to be ready to take care of infants immediately after they are born. That can mean carrying around babies weighing up to 20 percent of the father’s body weight.

Ziegler acknowledged that in humans, the changes could be purely psychosomatic.

“But if it occurs in two different species of monkeys, perhaps it is biological,” she said.

Ziegler noted that the male monkeys have higher levels of estrogen, prolactin and testosterone during the gestation of their mates. In male humans, levels of testosterone and the stress hormone cortisol are higher prior to the birth of a child than after.

What remains unknown is what may be triggering the changes.

“Women have an internal signal of pending motherhood – they are pregnant,” said Mark Erickson, an assistant clinical professor of psychiatry at the University of Washington School of Medicine. “Men do not.”

If there are changes that prepare men for fatherhood, presumably they are caused by some signal from the mother, Erickson said.

One possibility is that the changes are sparked by pheromones, aromatic chemicals secreted by a variety of animals, possibly including humans, that are sensed by other animals in the species and may lead to behavioral or physiological changes.

Of course, another explanation is that the weight gain is social. Men may simply be exercising less and eating more because their wives are.