BABIES born by elective caesarean are almost 2½ times more likely to die within their first month than babies born vaginally, researchers have found, adding weight to the argument that caesareans should only be carried out in emergencies.

The study, which involved more than 8 million births in the US over four years, is the first of its kind to focus on full-term babies born to women with no medical reason for choosing a caesarean over a vaginal delivery, an increasingly common phenomenon in Australia.

One in three babies is now born by caesarean section, up from about one in five 10 years ago, but those born before the onset of labour are often unresponsive and unable to breathe without help.

They are frequently admitted to neonatal intensive care units because their lungs cannot eliminate secretions and they lack catecholamines, a vital chemical secreted during labour that keeps them alert and eager to feed.

“We are designed to give birth vaginally. When will people wake up and realise this?” the secretary of the NSW Midwives Association, Hannah Dahlen, said yesterday. “When a baby is born vaginally, fluid is squeezed out of the lungs as it is pushed through the birth canal. The baby can then inhale with clean lungs, aerating its blood supply and kick-starting its circulation. A baby born by caesarean quite often comes out gurgling because its lungs are full of fluid, requires suction and is non-responsive because it lacks the hormonal surge delivered during labour.”

But babies born vaginally with high levels of catecholamines were usually alert and quick to seek out their mother’s breast. “They’ve got that ‘wow, I’m alive and I’m ready to go’ response.”

The study, published in the international journal Birth, only included women who had not had a previous caesarean; were giving birth to a single baby which was head down in the cervix; were between 37 and 41 weeks gestation and had none of the 16 common risk factors, such as diabetes or hypertension, associated with birth complications, in a bid to ensure that only low-risk births were evaluated.

It found the mortality rate for babies born vaginally was less than one in 1000 births while the rate for elective caesareans was 1.73 per 1000. A professor in obstetrics and gynaecology at the Australian National University medical school, David Ellwood, said the risk was still very small. “We have enough evidence now to know that caesareans should only be done when there is a medical indication, but when you look at the overall risk here, it is not that high.”

The clinical director of women’s and children’s health at the Sydney South West Area Health Service, Andrew Child, said the study should be treated with caution. “It’s been done by statisticians, not obstetricians or midwives,” he said.

Carolyn Constantian, 43, of Chatswood, delivered her twins, Amelie and Remy, by caesarean two weeks ago, but said she would have chosen a natural birth if she had been given an option. “I had to have a caesarean 2½ years ago when my daughter was born breech, but I tried everything to turn her around so I could give birth naturally. I just didn’t feel comfortable about having a caesarean then. Nor did I this time, but you have to do what’s right for your child.”