Around the world, cesarean births are on the rise, and many experts think that's a bad thing. Now, a new study looks at one way that babies delivered by c-section are different.

The number of surgical deliveries has been increasing for years. Some cesareans are medically necessary. But in other cases, women just want the convenience of knowing when they will give birth. For some, it's the modern thing to do.

Doctors like that predictability, too. And health care providers usually charge more.

A World Health Organization survey of hospital and clinic births in nine Asian countries earlier this year found 27 percent were c-sections, and in China it was nearly half of all births. And there were more deaths and complications when women had a cesarean delivery that wasn't medically required.

Other research has found c-section babies are more likely to have asthma or allergies.

Now, a small but intriguing new study looks at one way the delivery method might affect the baby's health. Co-lead author Elizabeth Costello, now at Stanford, was at the University of Colorado when the study was done.

"We were looking at effect of delivery mode on the very first bacteria that the baby is exposed to," Costello explained. "So we sampled babies literally seconds and minutes after they were delivered. So we're only looking at a snapshot of that very first moment in time."

To do that, Costello's co-lead researcher Maria Dominguez-Bello of the University of Puerto Rico took samples of bacteria from mothers and babies immediately before and after birth. Women who gave birth vaginally transferred the unique mix, their unique "community" of vaginal bacterial to the newborn baby.

"And that was in direct contrast with the c-section babies, who harbored bacterial communities that resembled human skin, but not their own mother's human skin any more than any of the other mothers in the study."

The researchers suspect that the newborn c-section babies might be picking up their generic bacteria mix from the air - one way bacteria gets on our skin.

Exactly how the differences in bacteria might make vaginally born babies less prone to allergies and asthma isn't yet clear, but it does point to a difference that researchers can look at going forward. Costello says she expects more studies as DNA analysis gets cheaper and faster.

So, does Costello's study support the notion that vaginal birth is somehow "better" than a cesarean? Speaking via Skype, she says no.

"I think further studies will be necessary to show whether the differences we've demonstrated depending on delivery mode of babies when they first emerge into the world actually carry over time, and whether those differences might contribute to health outcomes."

Elizabeth Costello's paper is published online by the Proceedings of the National Academy of Sciences.

vaginally: via the vagina 通过阴道

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（来源：VOA 编辑：陈丹妮）