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It has long been assumed that it is safer for women to deliver twins by cesarean section rather than vaginal birth.

But a new Canadian study shows that, in fact, the rate of complications and death is no greater with vaginal birth than C-section, meaning there is no reason to automatically opt for surgery.

"There's a perception among the public and the medical profession that cesarean is safer, but the study shows that's not true," Dr. Jon Barrett, chief of maternal fetal medicine at Sunnybrook Health Sciences Centre in Toronto, said in an interview.

The research, published Thursday in the New England Journal of Medicine, involved women in 25 countries who were pregnant with twins.

A total of 1,398 of the mothers-to-be (2,795 fetuses – the odd number is due to the fact that one woman turned out to not be carrying twins) were assigned to planned C-section, and 1,406 women (2,812 fetuses) to planned vaginal delivery.

Among women who planned to have a cesarean section, 91 per cent did so; among those who planned a vaginal birth, 43 per cent did so.

"This was an intention-to-treat analysis and, just as in the real world, plans change all the time," Barrett said. For example, if the first of the two twins was in a breech position – meaning feet or buttocks first, not head first – a cesarean was done.

Barrett and his team found that the risk of serious complications was virtually identical in the two groups, affecting 1.3 per cent of all babies. Complications included seizures, blood poisoning and the need for assisted ventilation.

The risk of death was also similar: 0.4 per cent of babies delivered by C-section and 0.3 per cent of those delivered vaginally.

In the study, 8.5 per cent of mothers who delivered vaginally had complications during birth, compared with 7.3 per cent of mothers who had a cesarean.

In an editorial also published in the New England Journal of Medicine, Dr. Michael Greene of the department of obstetrics and gynecology at Massachusetts General Hospital in Boston said that while the outcomes are the same, "these results do not indicate that all sets of twins should be delivered vaginally." Rather, he said that decision should rest with the obstetrician-gynecologist and that current practices – 75 per cent of twins born by C-section in the United States – should remain.

Barrett said he was dismayed by that view.

"Rather, I hope the findings will be a wake-up call, a reminder that natural birth should be the preferred option," he said.

The researcher said that, despite the common belief that surgery is cleaner and safer than a natural delivery, the reality is that surgery such as a cesarean section entails risks, including infections and complications for the mother; and the uterus can also be scarred, complicating subsequent pregnancies. Research also suggests C-section babies have a higher risk of diabetes and asthma.

But Barrett noted, in the U.S. in particular, that practice is often driven by fear of legal repercussions more than by evidence.

There are about 380,000 babies born in Canada annually; about 12,000 of those births are twins.