The Vaginal Microbiome and Pregnancy: What Does the Science Say?

What is the relationship between the vaginal microbiome and pregnancy?

Research is increasingly exploring whether the bacteria naturally found within the vagina, particularly Lactobacillus species, may be associated with fertility, pregnancy and pregnancy loss.

Here, we look at what the current scientific evidence tells us, what it doesn't tell us, and where probiotics fit into the research.

What is the vaginal microbiome?

The vagina naturally contains billions of microorganisms. Together, these make up the vaginal microbiome.

Unlike some other areas of the body, where having lots of different bacterial species is often considered beneficial, a healthy vaginal microbiome is commonly dominated by bacteria belonging to the Lactobacillus genus.

These bacteria help maintain the vagina's naturally acidic environment and can make it more difficult for potentially harmful microorganisms to become established.

However, everyone's microbiome is different and its composition can change over time.

Lactobacillus and pregnancy: why does it matter?

Researchers have become increasingly interested in whether the composition of the vaginal microbiome is associated with reproductive outcomes.

Lactobacillus species are particularly important because they help maintain the acidic vaginal environment and are commonly associated with a healthy vaginal microbiome.

The vaginal microbiome and miscarriage: what does the research show?

A systematic review and meta-analysis examining 43 studies found that Lactobacillus abundance was lower across the female reproductive tract in women experiencing miscarriage compared with controls.

The association was particularly apparent in studies of sporadic miscarriage.

However, the researchers also found substantial differences between studies and emphasised that methods for collecting and analysing microbiome samples need to become more standardised before firm conclusions can be drawn.

In other words, there appears to be an association, but that does not mean that low levels of Lactobacillus cause miscarriage.

The vaginal microbiome, fertility and IVF

The vaginal microbiome is also being investigated in fertility treatment.

Research involving assisted reproduction has found associations between a Lactobacillus-dominant vaginal microbiome and improved reproductive outcomes.

A systematic review and meta-analysis reported higher clinical pregnancy and live birth rates among women classified as having a favourable vaginal microbiome. However, the authors also highlighted limitations in the quality of the available evidence.

This is an exciting area of research, but an important distinction needs to be made:

An association does not prove that changing the vaginal microbiome will improve the chance of pregnancy or prevent pregnancy loss.

Can probiotics support the vaginal microbiome?

Because Lactobacillus species are associated with vaginal health, researchers have become increasingly interested in whether probiotics containing selected bacterial strains may help support the vaginal microbiome.

It is important to remember that probiotics are not all the same. Different products contain different bacterial species and strains, often in different quantities.

Evidence relating to one probiotic strain or formulation therefore cannot automatically be applied to another.

Research into probiotics, the vaginal microbiome and reproductive health is continuing, and further high-quality studies are needed to understand whether deliberately altering the vaginal microbiome can influence fertility or pregnancy outcomes.

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Are probiotics safe during pregnancy?

For most healthy people, probiotics are generally considered safe.

Studies examining probiotic use during pregnancy have not identified an increased risk of serious adverse pregnancy outcomes. Some people may experience mild effects such as changes in bowel habits or vaginal discharge, depending on the bacterial strains and product used.

Because probiotics contain live microorganisms, people with a significantly weakened immune system should seek medical advice before using them.

As with any supplement, if you are pregnant, undergoing fertility treatment or have an existing medical condition, speak to an appropriate healthcare professional if you are unsure whether a particular product is suitable for you.

What does the science tell us overall?

The vaginal microbiome is emerging as an important area of reproductive health research.

Current evidence suggests that:

• Lactobacillus species play an important role in maintaining the vaginal environment.

• Lower Lactobacillus abundance and greater bacterial diversity have been associated with some adverse reproductive outcomes, including miscarriage.

• A Lactobacillus-dominant microbiome has been associated with better outcomes in some fertility and assisted-reproduction studies.

• We do not yet know whether deliberately altering the vaginal microbiome improves pregnancy outcomes.

• Research into probiotics and reproductive health is continuing.

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Food supplements should not be used as a substitute for a varied, balanced diet and healthy lifestyle. This article is for general information only and is not intended to diagnose, treat or prevent any medical condition. If you are pregnant, trying to conceive or receiving fertility treatment, seek advice from an appropriate healthcare professional about supplements that may be suitable for you.