Another review reports 'vaginal seeding' may do more...

"Babies born via c-section do not benefit from vaginal seeding," reports the Mail Online.

Vaginal seeding is an increasingly popular practice in women who have given birth by caesarean section. It's based on the theory that caesarean-born babies have a higher risk of various illnesses than those born vaginally, as they were not exposed to bacteria in the birth canal.

It involves using a gauze swab to transfer vaginal fluid to the newborn baby, thereby exposing them to the bacteria.

But there is no credible evidence that vaginal seeding does any good and, as we discussed last year, it may actually expose babies to infection.

In this latest review, Australian researchers gave an overview of the pros and cons of vaginal seeding for caesarean-born babies, arguing that vaginal seeding is based on weak evidence, unnecessary and potentially unsafe.

There may be many reasons why caesarean-born babies appear to have a higher risk of some infections. For example, use of antibiotics during a caesarean may be a factor.

No methods were provided in the review, so we cannot be sure it included all the available research on the topic. But this is not the first time doctors have warned against the practice of vaginal seeding, and it is not recommended in the UK.

One way to protect your baby from infections is by breastfeeding. Read more about the benefits of breastfeeding.

Where did the study come from?

The study was carried out by researchers from The University of Western Australia, which – along with a scholarship from the Women and Infants Research Foundation of Western Australia – also funded it.

It was published in the peer-reviewed journal Frontiers in Medicine and is free to read online.

While the Mail Online's reporting was accurate, the headline – which also said the practice "may even transmit deadly viruses" – was a little alarmist.

The review provided no evidence of such transmission ever taking place. But to be fair to the Mail Online, this type of transmission, while probably rare, is possible.

What kind of research was this?

This was a narrative review discussing the theory of "bacterial baptism", where naturally born babies are exposed to vaginal bacteria in the birth canal.

Past studies have suggested that babies born by caesarean have a higher risk of infection and allergy because they lack this exposure, and this has led in some places to the practice of "vaginal seeding" to try to introduce bacteria to caesarean-born babies.

This review examined the research around these theories. However, no search methods or study-inclusion criteria were provided, so we cannot be sure if this was a systematic review that identified all the relevant literature on the topic.

What did the review say about differences in the bacteria carried by vaginally and caesarean-born babies?

There is evidence that the bacterial balance of a baby born via caesarean can differ from a baby born vaginally, but it is not clear why this is the case.

The researchers argued that if a baby's bacterial balance is affected by passage through the birth canal, then you would expect babies born vaginally to show colonisation (exposure) to vaginal bacteria in the first days of life – for example, in their skin, mouth or gut.

But most studies suggest any differences in the bacteria carried by vaginally and caesarean-born babies do not become apparent until about a week after birth.

There's also little evidence that babies born vaginally are colonised by greater numbers of vaginal bacteria. In fact, it's thought that any colonisation by vaginal bacteria occurs while the baby is in the womb, with the type of delivery making little difference.

What other factors may have an influence?

Several factors could have a role in the difference in bacteria between vaginal and caesarean babies:

antibiotics are administered as a preventative measure to all women having a caesarean – these could decrease the diversity of bacteria in the baby's gut
if a mother is having a planned caesarean, she does not go through labour – labour causes changes that could affect the baby's bacteria
women who have caesareans may be less likely to breastfeed – breastfeeding influences the baby's bacterial balance
obese women are more like to have a caesarean – a maternal diet higher in fat could alter the bacteria in the baby's gut

What did the review say about vaginal seeding?

The review said the data suggest it's not just "bacterial baptism" that causes differences in the bacterial balance of caesarean babies, and that research on vaginal seeding is "unconvincing and lacking in critical data".

Only very small studies have been conducted – for example, involving around 10 babies – and they have many limitations. The practice also has the potential to introduce some "unfriendly" viruses and fungi.

Conclusion

Overall, this review provides a convincing argument against the theory that differences in the bacteria of vaginally and caesarean-born babies solely result from exposure to the birth canal.

As the researchers explained, these differences could be influenced by many other factors, and there is very little evidence to support vaginal seeding.

The practice is not currently supported by doctors or midwives in the UK due to lack of evidence.