A PREGNANT woman is on a nine-month hormonal roller coaster鈥攁nd 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鈥� hormones also
fluctuate, and that the way they change mimics their partners鈥� 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鈥檚 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.
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Anne Storey of Memorial University in St John鈥檚, 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鈥� pregnancies.
鈥淭he differences for mums were much more drastic, but the patterns were
similar,鈥� says Storey. Testosterone dropped 33 per cent just after the baby鈥檚
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 鈥渟ympathetic
pregnancy鈥�, 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鈥檚 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鈥� 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.
鈥淭here鈥檚 something about the couple being together that sets the stage,鈥� she
says.