Written by Amy Goodwin. Reviewed by Jenny Wordsworth. Amy is a Physiology graduate with a background in Genetics and Human Life Sciences. Currently pursuing a master’s in Personalised Nutrition, she specialises in women’s health, fertility, and the microbiome’s role in nutrition.

Infertility is on the rise, with more women and people experiencing reproductive challenges due to conditions like endometriosis, polycystic ovarian syndrome (PCOS), and other disorders. On top of that, many people are waiting until later in life to start trying for a baby, which can complicate matters because fertility naturally declines with age. Even with the help of cutting-edge treatments like IVF, success rates remain stubbornly low. But there’s some good news: research into the reproductive microbiome could offer a promising route to improving outcomes.

What is the Microbiome, and Why Does it Matter?

The microbiome refers to the collection of microorganisms, like bacteria, fungi, and viruses, that live in and on our bodies. This includes the reproductive tract, where a healthy balance of microbes can be crucial in fertility and pregnancy. The reproductive tract refers to the system of organs involved in reproduction; ovaries, fallopian tubes, uterus, cervix, vagina, testes, epididymis (where sperm mature and are stored), seminal vesticles and prostate gland, penis. Understanding and altering the microbiome could pave the way for better fertility outcomes, including higher IVF success rates.

The Link Between Infertility and Microbial Imbalance

Studies show that women and people struggling with infertility often have a very different reproductive microbiome compared to those who conceive spontaneously. Imbalances in the vaginal microbiome, called dysbiosis, can increase the risk of infections, inflammation, and other issues, like altered cervical mucus, increased risk of STIs, endometrial health issues and poor implantation, that negatively affect fertility.

The vaginal microbiome changes over time due to factors like age, hormones, diet, and medications. However, during reproductive years, it’s usually dominated by the beneficial Lactobacillus bacteria. Lactobacillus is a genus of beneficial bacteria that help produce lactic acid, protect against pathogens, reduce inflammation, and support sperm survival and implantation. These helpful microbes create an acidic environment that prevents harmful bacteria from thriving. When the balance shifts, the risk of reproductive conditions like bacterial vaginosis, endometriosis, and PCOS increases, all of which can make it harder to conceive.

How Lactobacilli Support Fertility

Lactobacilli do more than keep harmful bacteria at bay; they actively support a healthy reproductive system. For example:

• Preventing infections: They form a physical barrier to stop pathogens from growing, keeping the vaginal environment acidic and unfavourable for harmful microbes.

• Supporting embryo implantation: Lactobacilli help create the ideal environment for an embryo to implant in the uterus, a key factor in both non-assisted conception and IVF success.

• Regulating the immune response: They modulate the immune system to allow for embryo implantation and protect against issues like miscarriage or preterm delivery.

• Promoting blood vessel growth: This supports the implantation process, which is critical for IVF success.

How Does the Microbiome Affect IVF?

IVF involves carefully transferring embryos into the uterus, but microbial imbalances can make this process less effective. They are particularly critical during embryo transfer, including frozen embryo transfer (FET). A disrupted vaginal or endometrial microbiome, especially low Lactobacillus levels and the presence of pathogenic bacteria , can reduce implantation rates, increase inflammation, and negatively impact endometrial receptivity. Vaginal dysbiosis has been linked to repeated implantation failures and recurrent pregnancy loss. Researchers are exploring ways to optimise the reproductive microbiome to improve IVF outcomes.

What Causes Reproductive Dysbiosis?

Several factors can disrupt the balance of microbes in the reproductive tract, including:

• Hormonal imbalances

• Diet and lifestyle

• Misuse of antibiotics

• Certain contraceptives

• Age and genetics

Can We Restore Microbial Balance?

Both antibiotics and probiotics are being explored as ways to improve the reproductive microbiome:

• Antibiotics: These can treat infections like bacterial vaginosis or chronic endometriosis, improving the uterine environment for embryo implantation. However, caution is needed to avoid overuse, as broad-spectrum antibiotics act against a wide variety of bacteria and may have harmful effects on advantageous bacteria such as Lactobacilli. Long-term use can also lead to resistance.

• Probiotics: These “good bacteria” supplements help restore balance by replacing harmful microbes. Some Lactobacillus strains show promise in reducing inflammation, preventing infections, and creating optimal conditions for conception and pregnancy. It is crucial to select probiotic strains with proven clinical efficacy, as not all probiotic strains offer the same health benefits.

A two-step approach may be particularly effective, using antibiotics to clear infections followed by probiotics to rebuild a healthy microbiome. Studies are also exploring novel techniques, such as applying specific Lactobacillus strains (Lactobacillus crispatus) directly to the catheter used in IVF procedures, although more research is needed.

The Key Takeaways

The health of the vaginal microbiome is essential for fertility. If you’re facing challenges, it’s worth considering whether microbial imbalances could be a contributing factor. Early detection and targeted treatments could help restore balance, improve your chances of conception, and support IVF success. This exciting area of research offers new hope for improving fertility and reproductive health.