By Amy Norton
Using brain imaging scans, researchers found that, compared with women who'd had a c-section, those who'd delivered vaginally showed greater activity in a number of brain regions in response to their own infants' crying.
The brain regions in question are thought to be involved in emotional regulation, empathy and habitual behaviours, among other things.
The findings, published in the Journal of Child Psychology and Psychiatry, raise the question of whether the method of delivery can affect a new mother's mood or behaviour soon after giving birth.
However, no one knows whether this is in fact the case.
"We don't know yet what this means," lead researcher Dr. James E.
Swain, of Yale University's Child Study Centre, said in an interview.
There is no evidence, he said, that women who have c-sections tend to have more difficulty bonding with their babies, for instance.
Instead, the little that is known often comes from animal research, with experiments showing that surgical delivery seems to alter how mothers tend to their pups. Some studies of women have linked c-section delivery to a higher risk of postpartum depression - but this relationship is controversial and not proven, Swain pointed out.
It is known that vaginal delivery triggers the release of a hormone called oxytocin, which is key in breast milk production and, in animals, has been shown to affect maternal behaviours like licking and grooming.
In theory, c-sections could - by altering the hormonal milieu of childbirth - affect human mothers' brain responses shortly after birth, according to Swain and his colleagues.
To test this idea, the researchers performed functional MRI brain scans on 12 healthy women who had given birth two to four weeks earlier. Half of the women had delivered vaginally and half underwent an elective c-section.
The scans charted changes in each woman's brain blood flow as she listened to either a recording of her own baby crying or to static-like sounds.
In general, the study found, the mothers who'd delivered vaginally showed greater activity in response to their babies' cries within several regions of the brain.
Much more research will be necessary to sort out what all of this means, according to Swain. He and his colleagues are continuing to follow the women in their study to see whether differences in brain activity persist.
There is also a need for larger studies that include not only healthy women, as this one did, but mothers with postpartum depression as well, Swain pointed out.
If c-sections do affect maternal brain activity and behaviour, the researcher noted, it would stand as one more factor for women and their doctors to consider when deciding whether to have an elective cesarean.
It would also suggest, Swain said, that doctors, husbands and families should "give a little extra consideration and care to moms who have c-sections."