Mothers who push to give birth may be more responsive to the cry of their babies than those mothers who elect to have a caesarean birth, a brain-scanning study suggests.

When U.S. researchers looked at functional MRI brain scans taken up to a month after mothers gave birth and heard their own babies' cries, they found more activity in areas linked to motivation and emotion among the six who had vaginal deliveries compared with six who had caesarean sections.

"We wondered which brain areas would be less active in parents who delivered by caesarean section, given that this mode of delivery has been associated with decreased maternal behaviours in animal models, and a trend for increased postpartum depression in humans," said the study's lead author, Dr. James Swain of the Child Study Centre at Yale University in Connecticut.

"Our results support the theory that variations in delivery conditions such as with caesarean section, which alters the neurohormonal experiences of childbirth, might decrease the responsiveness of the human maternal brain in the early postpartum."

The differences in brain activity were found in regions that seem to affect how a mother responds to her child and regulate her mood.

Postpartum depression risk

In natural birth, contractions help trigger the release of the hormone oxytocin, which is thought to shape a mother's behaviour. Hormones are not released in the same way during a caesarean section.

Obstetricians have long known that women who have a caesarean section sometimes have problems bonding with their baby.

That's why doctors and nurses on maternity wards commonly advise women to cuddle newborns against their skin right after birth to establish a bond, and offer support for feeding and care for the baby.

It is possible that the clinical reasons that lead women to have C-sections may play a role. To rule that out, researchers studied six mothers who opted to have C-sections, rather than cases where the procedure was medically necessary.

The study appears in the October issue of the Journal of Child Psychology and Psychiatry.

The number of women giving birth by C-section in Canada rose to 26 per cent in 2005-06 from 23 per cent in 2001-02, according to a report by the Canadian Institute for Health Information.

"As more women opt to wait until they are older to have children, and by association be more likely to have a caesarean section delivery, these results are important, because they could provide better understanding of the basic neurophysiology and psychology of parent-infant attachment," said Swain.

"This work could lead to early detection of families at risk for postpartum depression and attachment problems and form a model for testing interventions."