Auckland researchers are launching a study aimed at showing whether caesarian-section births are linked to asthma and obesity in children.
It's widely speculated that the two are associated as more becomes known about bacterial or bugs in our gut, and what it does to our health.
A third of all adults in New Zealand are obese, and a third of all children are overweight or obese in this country on the day they begin school.
Researchers at Auckland University's Liggins Institute now suspect there may be a link between gut flora, also known as the microbiome, and obesity.
Lead researcher Wayne Cutfield wants to find out whether suggestions that births by caesarean section could be linked to a higher risk of obesity is true.
"The speculation is that babies born by caesarian section are not exposed to their mother's vaginal and perineal microbiome, during that delivery process," Prof Cutfield said.
"Babies have a relatively sterile gut just before they're born and clearly the early colonisation of that gut microbiome is really important."
He said babies born by elective caesarian section are "not going to be exposed to their mother's microbiome, and their gut will be populated by environmental bacterial, which are probably less healthy. So that's what's been proposed is the reason for the link between caesarian [birth] and a 30 percent increased risk of childhood obesity, and in fact a 30 percent increased risk of asthma as well."
He's about to test whether there are differences in the gut bacteria between C-section babies who have been given a small amount of their mother's microbiome shortly after birth, and C-section babies who have not received the treatment.
"What we're going to do is take the mothers' secretions - vaginal and perineal secretions - put them into a sterile water solution and give them to the babies orally, because when babies are born for several hours their stomach is not acid," Prof Cutfield said.
He said adults' stomachs were very acid, which would kill such bacteria.
"But just for several hours after a baby is born its stomach isn't acidic and the bacteria will be swallowed and go down to the bowel where we want them to be."
Latest provisional figures from the Health Ministry show there were 16,423 C-section births in this country last year, and that the percentage of these elective caesarian sections increased from 10.3 percent in 2008 to 12.6 percent last year.
Prof Cutfield said many twins were born by elective C-section, and the study was recruiting twins for the trial through obstetric groups which have registries of these situations.
"If the study is positive and the treatments with the mothers' microbiome actually improves the health and wellbeing of the children in terms of obesity and asthma, it's going to be a simple thing to scale up and do."
An Auckland obstetrician, Nicholas Walker, said one in 20 of his C-section patients asks for a procedure known as "seeding", where the mother's microbiome is transferred to the baby shortly after birth, using a swab technique: "After the birth of the baby, usually within half to one hour, there's a chance to take the swab and gently paint the baby's nose and mouth, lips, ears and eyes and the bottom area of the baby where the bacteria would essentially try to enter the baby's body."
Dr Walker said those who request this have thought about it and strongly want it.
He said bacteria like e-coli and group B streptococcus can be associated with mother's microbiome secretions, but that could be the case with vaginal birth too.
"I don't think there's evidence of harm from it, and there may be benefit, and so in the absence of harm I think it's reasonable to do," he said of the "seeding" procedure.
An Auckland mother, and health professional, whom RNZ agreed to call "Susan", said she did it herself for her first baby two and a half years ago, and had it done by her obstetrician for the birth of her second child, by C-section, for medical reasons, 10 days ago.
"I can't control very much what happens about my children's birth but this was sort of something I could contribute to and hopefully it made a difference," Susan said.
She said both children were doing fine.
"I think they're wonderful. I think that it's pretty hard to say if the seeding has had any effect on them so far but I guess it was one thing I could control in a fairly uncontrollable situation of not really being able to choose how they were born."
Prof Cutfield said they would know within a year to 15 months if gut bacteria was different in children born from C-sections who were treated and not treated.
However, whether C-sections do increase the risk of obesity would not be known for up to five years.