From: New Scientist

When Dads go gooey-eyed, blame their hormones

A PREGNANT woman is on a nine-month hormonal roller coaster-and it turns out that the father of her child goes along for the ride. Researchers in Canada have shown for the first time that expectant fathers' hormones also fluctuate, and that the way they change mimics their partners' ups and downs.

During pregnancy, levels of several hormones rise in an expectant mother. These include prolactin, which triggers lactation; the stress hormone cortisol, which is known to be related to a mother's attraction to her child; and the main female sex hormone, oestradiol. Immediately after the birth, the levels crash. These hormonal changes are thought to be driven by the development of the baby in the womb.

Recently, however, studies in certain animals, including most birds, some rodents and even a few primates, have shown that fathers are also hormonally primed for the birth of their young (New Scientist, 12 December 1998, p 38). But until now no one knew whether the same was true for men.

Anne Storey of Memorial University in St John's, Newfoundland, and her colleagues wanted to find out. They recruited 34 couples from an antenatal class in a Newfoundland hospital and took blood samples at different times during and after the pregnancies.

Twelve couples were sampled in the fourth or fifth month, eight in the last month, nine three weeks after the birth, and eight between three and six weeks after the birth. Most of the volunteers gave samples just once, but two couples gave blood before and after the birth, and one couple donated 10 blood samples at different times during the pregnancy. The researchers found that in fathers, levels of cortisol, prolactin and testosterone changed significantly during their partners' pregnancies.

"The differences for mums were much more drastic, but the patterns were similar," says Storey. Testosterone dropped 33 per cent just after the baby's birth, and lower levels of testosterone were associated with men becoming more parental, they found. They will report their results in a future issue of the journal Evolution and Human Behavior.

The team also asked fathers about changes that might signal a "sympathetic pregnancy", such as fatigue, change of appetite and weight gain. Fathers who reported these symptoms also had higher prolactin levels and a steeper drop in testosterone than those who did not have these symptoms.

The researchers also studied short-term changes. After giving a blood sample, volunteers listened to a six-minute tape of a newborn's cries and watched a video about the trials of learning to breastfeed. Thirty minutes later, their blood was sampled again. The researchers found that the men experienced pronounced hormonal changes after exposure to the baby cues. Like mothers, fathers' cortisol plummeted.

Storey speculates that a combination of behaviour and pheromones from a pregnant woman somehow prompts the father to prepare for the birth of his child. "There's something about the couple being together that sets the stage," she says.

Author: Alison Motluk

New Scientist issue 8th Jan 2000


This article comes from Science Blog. Copyright 2004