Microbirthing, which involves taking a swab from the mother's vagina and wiping this over the baby's mouth, eyes, face and skin shortly after birth by Cesarean section, is a growing fad, but there is no evidence this 'vaginal seeding' does anything positive, according to an editorial in the BMJ. Around one in four babies are born via caesarean section in the UK. 

The idea is that vaginal seeding allows a baby born via Cesarean section to come into contact with bacteria from the birth canal. The hope is this may boost their gut bacteria, and reduce risk of conditions such as allergies or obesity. Basically, it appeals to the same logic as homeopathy and organic yogurt. 
Often the husband or partner undertakes the swabbing process, but in some cases parents have asked medical staff to perform the procedure. 

Dr. Aubrey Cunnington from the Department of Medicine at Imperial College London, and lead author of the BMJ article, says that due to lack of evidence, medical professionals should not recommend or encourage the practice. Like with consuming afterbirth, there could be harmful bacteria. In the case of microbirthing, such as group B streptococcus, to the baby via the swab. Although this is the same bacteria a baby would be exposed to during a vaginal birth,  Cunnington says staff would not realize a baby has been exposed to this bacteria, should a newborn fall ill.

"Demand for this process has increased among women attending hospitals in the UK - but this has outstripped professional awareness and guidance. At the moment we're a long way from having the evidence base to recommend this practice. There is simply no evidence to suggest it has benefits - and it may carry potential risks. Its important parents tell staff they have performed the procedure, so the healthcare team are aware the baby is at risk of the same infections as a baby born by vaginal delivery." 

The practice seems to have started because of epidemiological claims based on data suggesting babies born by Cesarean section have a slightly increased risk of conditions in later life such as obesity, allergies and even autoimmune disease, such as inflammatory bowel disease. 

Then add in wacky claims about microbiota and supplement makes claiming these babies have a different microbiome (the collection of trillions of bacteria living in our guts) than those born vaginally. Some speculate this may be because the bacteria the baby is exposed to in the birth canal during a vaginal birth colonize the baby's gut. This helps to protect them against conditions such as allergies.

"The theory is that by transferring bacteria from mum to baby, these bacteria can then make their way to the baby's gut and alter the bacteria in their tummy - called the microbiome. There is now quite a lot of evidence that differences in the microbiome are associated with risk of developing conditions such as allergies and obesity. However people have made a leap of logic that gut bacteria must be the link between Cesarean section and risk of these diseases. But we just don't know this for sure - or whether we can even influence this by transferring bacteria on a swab from mum to baby," says Dr. Cunnington.

He adds there is only one ongoing study into vaginal seeding, which is examining whether the practice can change a baby's gut microbiome. But in the study, scientists are testing the mothers for potentially dangerous bacteria, which would not happen in a routine hospital setting. 

"In some countries, including the UK, we don't test pregnant women for the bacteria group B streptococcus. This is carried by around one in four pregnant women, and although it poses no risk to the mother it can cause fatal infections in babies. There are also other conditions that cause no symptoms in the mother, such as chlamydia, gonorrhea and herpes simplex virus that could be transferred on the swab. One colleague had to intervene when a mother with genital herpes, who had undergone a Cesarean section, was about to undertake this process. Swabbing would have potentially transferred the herpes virus to the baby.

"Doctors, nurses, midwives and parents need to be aware they are doing something with a potential risk that currently doesn't have any evidence of benefit."

He adds that other factors can also affect a baby's microbiome: "Encouraging breast feeding and avoiding unnecessary antibiotics may be more important to a baby's gut bacteria than worrying about transferring vaginal fluid on a swab."