The Vaginal Microbiome: Its Role in Conception and Fertility

The vaginal microbiome, which is a community of microorganisms living in the vagina, plays a crucial role in reproductive health. It significantly affects the vaginal environment, impacting sperm movement and survival. A healthy microbiome, dominated by Lactobacillus bacteria, creates a favourable environment for sperm, aiding in successful fertilization. On the other hand, an imbalance in the microbiome, known as dysbiosis, characterized by an overgrowth of harmful bacteria like Gardnerella vaginalis, can disrupt this balance and hinder conception.

Composition and Function of the Vaginal Microbiome

  1. Composition

The vaginal microbiome mainly consists of Lactobacillus species, such as Lactobacillus crispatus, Lactobacillus jensenii, Lactobacillus gasseri, and Lactobacillus iners. These bacteria are essential for maintaining an acidic vaginal environment (pH 3.5-4.5) by producing lactic acid, which prevents the growth of harmful microorganisms. The microbiome also includes other bacteria like Gardnerella vaginalis and Atopobium vaginae, fungi like Candida species, and viruses.

  1. Function

The vaginal microbiome has several key functions:

  • Protection Against Pathogens: Lactobacillus bacteria help maintain an acidic environment that protects against harmful bacteria and fungi.
  • Immune System Interaction: The microbiome interacts with the immune system, helping to control inflammation and maintain overall vaginal health.
  • Reproductive Health: It influences factors like lubrication, pH balance, and the health of vaginal tissues, all of which are crucial for fertility and healthy pregnancies.

Changes in the Vaginal Microbiome During the Menstrual Cycle

The vaginal microbiome changes throughout the menstrual cycle due to hormonal variations, particularly oestrogen and progesterone levels. These changes affect the vaginal environment and microbiome composition.

  1. Menstrual Phase

During menstruation, oestrogen and progesterone levels are low. This leads to:

  • Reduced Lactobacillus: The influx of menstrual blood raises the vaginal pH, temporarily reducing Lactobacillus levels.
  • Increased Diversity: This reduction can lead to a temporary increase in other bacteria, including Gardnerella vaginalis.
  • Increased Infection Risk: The less acidic environment increases susceptibility to infections.
  1. Follicular Phase

As oestrogen levels rise in preparation for ovulation:

  • Lactobacillus Recovery: Increased oestrogen boosts glycogen production in vaginal cells, which Lactobacillus bacteria ferment to produce lactic acid, restoring a low pH and Lactobacillus dominance.
  • Stabilization: The microbiome stabilizes, maintaining a protective environment against pathogens.
  1. Ovulatory Phase

At ovulation, oestrogen peaks and luteinizing hormone surges:

  • Enhanced Lactobacillus Activity: High oestrogen levels support Lactobacillus growth, ensuring an acidic environment conducive to sperm survival and motility.
  • Optimal Conditions for Conception: The microbiome is most stable and Lactobacillus-dominant, providing the best conditions for fertilization.
  1. Luteal Phase

After ovulation, progesterone rises while oestrogen declines:

  • Potential Dysbiosis: Increased progesterone can alter vaginal secretions and pH, leading to slight dysbiosis.
  • Immune Modulation: Progesterone reduces local immune responses, potentially allowing non-Lactobacillus bacteria to increase temporarily.
  • Stabilization: Toward the end of the cycle, the microbiome may stabilize again, though this varies among individuals.

Effects of the Vaginal Microbiome on Fertility

A healthy vaginal microbiome supports sperm survival and motility, which are crucial for conception.

Importance for Sperm

  • Protection Against Pathogens: An acidic environment inhibits harmful bacteria and fungi, reducing infection risks that could harm sperm.
  • Enhanced Sperm Motility: A low pH helps sperm move through cervical mucus and reach the egg.
  • Preservation of Sperm Viability: The acidic environment protects sperm membranes, improving their chances of fertilizing the egg.

Dysbiosis and Its Impact on Conception

Dysbiosis can create a hostile environment for sperm by raising vaginal pH and promoting pathogen growth.

Causes of Dysbiosis

  • Antibiotic Use: Antibiotics can kill beneficial bacteria, reducing Lactobacillus populations and increasing harmful bacteria.
  • Hormonal Changes: Fluctuations in oestrogen and progesterone during the menstrual cycle, pregnancy, and menopause can affect the microbiome.
  • Lifestyle Factors: Poor diet, stress, smoking, and douching can disrupt the microbiome.
  • Sexual Activity: Unprotected sex and multiple partners can introduce new bacteria, disrupting the balance.

Consequences of Dysbiosis

  • Elevated Vaginal pH: Pathogenic bacteria can raise pH, degrading protective mucus and making the environment less acidic.
  • Pathogen Overgrowth: Increased pathogens can cause infections like bacterial vaginosis, creating inflammation that disrupts sperm function.
  • Increased Inflammation: Dysbiosis can trigger inflammation, damaging vaginal tissues and creating a hostile environment for sperm.
  • Biofilm Formation: Pathogens can form biofilms, making them resistant to treatment and further disrupting the environment.

Implications for Fertility

  • Reduced Sperm Motility: Elevated pH and pathogens can hinder sperm movement.
  • Decreased Sperm Viability: Pathogens and inflammation can damage sperm, reducing their ability to fertilize the egg.
  • Increased Infection Risk: Infections can damage the reproductive tract, making fertilization more difficult.

Implications for Assisted Reproductive Technologies (ART)

For couples undergoing ART like IVF, the state of the vaginal microbiome can affect outcomes. Addressing microbiome imbalances before ART can improve success rates.

Diagnostic Testing for Vaginal Microbiome Imbalances

Standard Methods

  • Microscopy: Examines vaginal discharge to identify clue cells and assess microbiome composition.
  • Culture Techniques: Identifies and quantifies specific bacteria and fungi.

Advanced Methods

  • PCR: Detects and quantifies specific bacterial species.
  • Next-Generation Sequencing (NGS): Provides comprehensive microbiome profiles, identifying known and novel microorganisms.
  • 16S rRNA Gene Sequencing: Offers detailed taxonomic information on bacterial communities.

Treatment Approaches


Probiotics, especially those with Lactobacillus strains, can restore and maintain a healthy microbiome. They can be taken orally or vaginally to promote beneficial bacteria growth and reduce pathogenic species.

Antibiotics and Antifungals

In severe dysbiosis or infections, antibiotics and antifungals are prescribed. However, these treatments can disrupt the microbiome, so probiotics are often recommended afterward to restore balance.


Prebiotics are non-digestible carbohydrates that promote beneficial bacteria growth. They can be used with probiotics to enhance their effects.

Lifestyle and Dietary Modifications

Diet and lifestyle significantly impact the microbiome. A diet rich in fibre, fruits, and vegetables supports microbial health. Avoiding excessive antibiotics, maintaining good hygiene, and reducing stress can also help.