Dr. Moira Bradfield Strydom (PhD, M.Acu, B.Nat) shares what you need to know about \the vaginal microbiome and miscarriage. 

Pregnancy can be a beautiful and transformative time, but it also often brings uncertainty, especially if you’ve experienced loss before. Miscarriage, particularly in the first trimester, is far more common than we often acknowledge, and it’s rarely due to a single cause. While chromosomal issues are a major factor, there’s growing evidence that the vaginal microbiome may also influence pregnancy outcomes.

Understanding the vaginal microbiome as part of the broader picture, alongside hormones, nutrition, partner health, emotional wellbeing and lifestyle, can help create a more supportive and holistic environment for conception and pregnancy. For those planning to conceive or navigating pregnancy after loss, exploring your vaginal microbiome can be a proactive and empowering step.

What is the Vaginal Microbiome
The vaginal microbiome is a highly dynamic, hormonally responsive ecosystem made up predominantly of Lactobacillus species. These bacteria actively protect the vaginal environment by producing lactic acid, hydrogen peroxide, and bacteriocins that suppress pathogens. This maintains a naturally acidic pH (typically 3.6 to 4.5), which discourages the growth of bacteria, fungi, and viruses that don’t belong.

This microbial community is not static. It constantly adapts to internal signals and external exposures, influenced by factors such as:

• Hormonal landscape:

  • Estrogen promotes glycogen in vaginal cells, feeding Lactobacilli

  • Puberty initiates microbiome maturation

  • Ovulation generally supports Lactobacillus dominance

  • Menstruation’s higher pH can disrupt balance

  • Perimenopause and menopause reduce estrogen, lowering Lactobacillus and raising pH

  • Pregnancy can either amplify pre-existing imbalances or promote Lactobacillus dominance, though it may also increase susceptibility to fungal issues like thrush (Bradfield Strydom et al., 2023)

• Sexual activity:

  • Semen (pH ~7.1–8) can temporarily alkalise the vaginal environment, destabilising the microbiome for some

  • Microbial sharing and frequency of intercourse also play a role

  • A recent Australian study found that BV-associated microbes are shared between partners, and treating the male partner’s penile and seminal microbiome may reduce recurrence risk (Vodstrcil et al., 2025)

• Hygiene practices:

  • Over-cleansing, douching, or using scented products can disturb vaginal pH and mucosal health

• Gut and general health:

  • A gut-vaginal axis exists. Gut dysbiosis (like constipation, SIBO, or low diversity) can impact vaginal immunity and inflammation systemically

• Medications:

  • Antibiotics, hormonal contraceptives, and antifungals can all shift microbial balance, sometimes for the better, sometimes not

• Stress and immunity:

  • Chronic stress can alter mucosal immunity and reduce Lactobacillus resilience

When Lactobacillus dominance is lost, the vaginal microbiome may shift toward a BV (bacterial vaginosis) pattern, often involving Gardnerella vaginalis, Atopobium/Fannyhessia, and Mobiluncus. BV not only causes odour and discharge, but it also increases vulnerability to STIs, pelvic inflammatory disease, miscarriage, and preterm birth (Ferrante et al., 2025).

BV and Pregnancy Risks
BV is marked by a decline in protective Lactobacillus species and an overgrowth of anaerobic bacteria such as Gardnerella, Fannyhessia, Sneathia, and Prevotella. These bacteria generate inflammatory compounds that can damage vaginal tissue, degrade cervical mucus, increase cervical contractility, and potentially lead to miscarriage via ascending infection into the uterus.

A 2022 study in BMC Medicine (Grewal et al.) found that people with chromosomally normal miscarriages had distinct vaginal microbiota profiles compared to those with successful pregnancies, further highlighting how critical a healthy vaginal microbiome can be.

Additionally, conception success, both natural and assisted, is higher when the vaginal microbiome is Lactobacillus-dominated and stable (Maleki-Hajiagha et al., 2025; Tan et al., 2025).

Proactive Steps for Vaginal Health

1. Microbiome Screening
   If you’ve experienced recurrent BV or miscarriage, consider vaginal microbiome testing, ideally before conception, but it can also be done during pregnancy. Your GP can perform standard swabs and microscopy, or more comprehensive testing can assess microbial diversity and risk patterns.

2. Probiotic Support
   Probiotics containing strains like Lactobacillus crispatus show promise in restoring a healthy microbiome. Research confirms both oral and vaginally inserted probiotics can be effective in reducing BV risk (Udjianto et al., 2025).

3. Safe Sexual Practices
   Using protection can help maintain pH balance. If you’re trying to conceive, focus on improving both partners’ microbiome health before conception, including the seminal and penile microbiome.

4. Consult Healthcare Providers
   If you’re concerned, pregnant or planning, speak with a qualified healthcare provider. Individualised care can make a meaningful difference in how you feel supported.

While not all miscarriages can be prevented, understanding and nurturing the vaginal microbiome is a powerful step toward protecting your reproductive health. Awareness and early action matter.

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