File photo: The practice became popular among British mothers after a documentary called Microbirth was screened in 2014. Picture:

London - A birth technique designed to protect babies from asthma and allergies could actually harm newborns, experts warn.

Doctors said there was no evidence that transferring "protective" bacteria from the mother’s birth canal after a caesarean section helped babies fight infection.

Instead they warned that the procedure – microbirthing or vaginal seeding – could give babies deadly infections and sepsis.

The practice became popular among British mothers after a documentary called Microbirth was screened in 2014.

It said that because babies born by caesarean section did not pass through the birth canal, they did not pick up any of the protective bacteria from their mother that could help to kickstart their immune systems.

As a result, concerned mothers began asking for swabs from the birth canal to be applied to their newborn’s eyes, face and skin after a caesarean section. The procedure can either be carried out by the mother, her partner or a nurse.

As one in four British babies are now born by caesarean section – one of the highest rates in the world – microbirthing has become increasingly popular.

But a review by the Danish Society of Obstetrics and Gynaecology said it could put babies at risk. Lead author Dr Tine Dalsgaard Clausen, a consultant obstetrician, said: "There is no evidence to show that the potential long-term benefits of vaginal seeding outweigh the risks or costs."

But she said there was a chance that babies could be put at risk of sexually-transmitted diseases and serious infections, including HIV, chlamydia, gonorrhoea, herpes, group B strep and E.coli – a leading cause of sepsis in newborns.

Screening mothers for bacteria ahead of birth could help reduce this risk. Instead, the doctors recommended placing the newborn baby on the mother or father’s skin and breastfeeding, both of which boost babies’ immune systems.

Professor John Thorpe, of the journal BJOG, which published the study, said: "This research should help reassure women who’ve had a caesarean section that the practice of vaginal seeding is unnecessary and there are other ways to help give their baby the best start in life."

Dr Patrick O’Brien, consultant obstetrician and spokesperson for the Royal College of Obstetricians and Gynaecologists, said: "There is no robust evidence to suggest that vaginal seeding has any associated benefits, and we would therefore not recommend it until more definitive research shows that it is not harmful and can in fact improve a child’s digestive and/or immune system.

"It is also important to note that some vaginal bacteria can be passed on to the baby, occasionally causing illness."