Scientists are set to investigate the role of mothers' bacteria in babies' early health.
The University of Auckland's Liggins Institute will give one half of twin babies born by C-section the vaginal bacteria they would pass through in a natural birth, but miss out on.
Study lead Wayne Cutfield says it's the first controlled test of its kind.
"What we're studying are twins where one twin is treated with the mother's bacteria, and the other is not. The first step is to show there are differences indeed in their bacteria that get established."
Babies born by C-section have a greater risk of getting asthma and eczema, and are also likely to be obese later in life.
"Babies born by caesarean miss out on the normal process of exposure to these bacteria, which happens during a vaginal birth," the study page on the University of Auckland website reads. "The bacteria are an important part of developing babies' digestive and immune systems. The study is trying to see if mimicking the normal process can help babies born by caesarean."
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Cutfield says the study could benefit thousands.
"One-in-four babies in New Zealand is born by Caesarean section, and in specialist referral centres, it's about one-in-three."
He says it's the first study of its kind.
"This study will be really informative to pregnant women who may or may not be undergoing Caesarean section, and to obstetricians and midwives."
Researchers are also looking for women having a single baby to act as part of a control group.
More information and how to get involved can be found on the University of Auckland website.