This is a great question and one that scientists have given significant attention in recent years.

We know the vaginal microbiome is dominated by a number of genus, including Lactobacilli3. If balanced, these bacteria provide a natural barrier against bacterial and viral pathogens and help to maintain a healthy vaginal pH.

Pregnant woman
During pregnancy, the vaginal microflora undergoes a series of changes

We also know that once a woman falls pregnant, and as the pregnancy progresses, the vaginal microflora undergoes a series of fascinating changes. At the beginning and towards the middle of gestation the bacterial composition becomes less diverse, in favour of Lactobacilli bacteria.2 This is thought to be a deliberate mechanism for limiting intimate infections, which can cause complications during pregnancy.3 As women progress towards birth this bacterial composition changes again, increasing in diversity so that Lactobacilli bacteria no longer dominate, and the bacterial composition of the vaginal microbiota returns to resemble that of a non-pregnant woman.

It’s been suggested that these changes are as a result of hormonal changes and that the consequent migration of Bifidobacteria to the vaginal tract from the gut is a deliberate ‘gathering’ of bacteria in preparation for birth.

You might remember that in 2014 Joanna wrote a blog post highlighting a documentary film, Microbirth, which investigated the link between a natural birth and our microbiome, and its impact on health and immunity. She explored the idea that bacteria gather in the mother’s vaginal tract pre-birth and that the new-born is ‘seeded’ at birth with the mother’s microbiome – a process the programme-makers referred to as ‘maternal heritage’.

Microbirth poster
Microbirth explores the link between a natural birth and our microbiome

How an individual is born then, whether a vaginal birth or via C-section, has the potential to affect that person’s lifelong microbiome. Interestingly, in a recent interview, Dr Aagaard, from the Texas Children’s Hospital and Baylor College of Medicine in Houston, argued that as much attention needs to be paid to what is happening prior to the birth, in the 40 weeks of pregnancy – ‘as this may be as important or even more than how the baby comes out’.1

For a long time, it was thought that the womb was sterile but we now know that the placenta also harbours a unique ecosystem of bacteria from the mother. It follows that this bacteria is passed to the baby via the blood, and although Dr. Aagaard is sceptical that this was an evolutionary design, she agreed that this knowledge could be used to our advantage, potentially in preparing the fetal immune system.

Although more research is needed, these studies support the message that throughout pregnancy, during labour and beyond, the gut and vaginal microflora are hugely relevant to mum and baby and their health.

If you'd like to learn more about bacteria and the placenta you can read Kathy's excellent blog: 'Do babies come into contact with bacteria in the womb?'


1. Aagard, K Dr. (2016), 'Interview with Kjersti Aagaard on gestational influences on the early microbiota', Interview with Dr. Aagaard by Cristina Sáez, Gut Microbiota News Watch, 13 OCT 2016.

2.Romero, R. et al. (2014). The composition and stability of the vaginal microbiota of normal pregnant women is different from that of non-pregnant women. Microbiome. 2049-2618

3.Spurbeck, R. R., and Arvidson, C. G. (2010). Lactobacillus jensenii surface associated proteins inhibit Neisseria gonorrhoeae adherence to epithelial cells. Infect. Immun. 78, 3103–3111

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