Fertility & Postpartum

Professor Willa Huston is a microbiologist at the University of Technology Sydney. Her research team is committed to understanding how STIs and the vaginal microbiome are involved in infertility and other adverse impacts on women’s reproductive and genital health. She said:

"In the not too distant future you might be encouraged by your doctor to give some thought to your microbial friends in your vagina!"

1. Vaginal microbiome during conception and implantation

A woman's body produces multiple sex hormones that work together to create the optimal environment for egg production, ovulation, fertilization, conception, and pregnancy. At the same time, the reproductive tract is equipped with an immune system regulated by these hormones, programmed to recognize and respond to any foreign substance or object. This ensures protection against intruders and infections.

However, sometimes the body mistakenly identifies a newly fertilized egg as an intruder. When hormonal balance and immune system coordination function correctly, the body naturally resolves this issue by gently suppressing immune activity in the reproductive tract. This occurs during the luteal phase of the menstrual cycle—the second half, following ovulation—helping to create the ideal conditions for implantation. Each menstrual cycle fine-tunes the delicate interplay between hormones and the immune system, adjusting the structure of reproductive organs to foster a supportive environment for implantation while minimizing any interference caused by an overly protective immune response.

Yet, this immune suppression makes the reproductive tract more vulnerable to vaginal infections. As a result, the process of conception carries inherent risks to the balance of the vaginal microbiome and overall vaginal health (1). However, women's bodies already have a solution, as the vaginal microbiome undergoes significant changes during pregnancy.

2. Vaginal microbiome during pregnancy 

A woman's body is an incredible ecosystem, designed to handle the complex processes of pregnancy while working tirelessly to protect and strengthen both mother and baby. Research has shown that pregnant women have a higher abundance of beneficial bacteria essential for a healthy vaginal microbiome - specifically Lactobacillus crispatus and Lactobacillus gasseri. This suggests that a healthy vaginal microbiome in pregnant women tends to be more stable and resilient than in non-pregnant women (2).

Lactobacillus are the good, healthy bugs that help to maintain balance and healthy bacterial populations in the vagina. Lactobacillus species produce lactic acid, hydrogen peroxide and other directly antimicrobial agents. There are around 20 Lactobacillus species that have been detected in the vagina. Recent scientific research has shown that healthy vaginal microflora does not contain high numbers of many different Lactobacillus species. Rather, 1 or 2 Lactobacillus species are dominant (mainly L. crispatus and L. iners but also L. gasseri and L. jensenii), and other species are rare. 

Lactobacillus crispatus

The most important of the Lactobacillus species is called Lactobacillus crispatus. In fact we like to call it ‘the queen'. It is the most beneficial healthy bacteria in vaginal microbiome of 65% of all women. If you get back a vaginal microbiome test, and see L. crispatus dominance in the results it will usually indicate that there is a balanced and healthy vaginal microbiome. L. crispatus creates very stable colonies. 

Lactobacillus gasseri

Lactobacillus gasseri is the ‘second in command’ good bug, entirely connected with the healthy and balanced vaginal microbiome. It is present in healthy vaginal microbiome in more than 40% of women. Although it does not create as stable colonies as L. crispatus, certain L. gasseri strains have the ability to release antimicrobial substances that interfere with the ability of bad bugs to survive in the vagina and form a biofilm (a protective layer some bad bugs can create around themselves).

3. Vaginal microbiome postpartum

The research shows that the vaginal microbiome composition dramatically changes postpartum to become less Lactobacillus spp. dominant independent of ethnicity. The vaginal microbiome also becomes more diverse, meaning that there are wider range of bacterial species present, moving the microbiome shift toward disbalance. This is due to the physical impact of childbirth, significant hormonal fluctuations, and the increased exposure of the vaginal environment to new microorganisms.

Source: MacIntyre et al. (2015). The vaginal microbiome during pregnancy and the postpartum period in a European population.

A study conducted in the UK on 42 pregnant women of European, African, and Asian ethnicity tracked changes in their vaginal microbiome throughout pregnancy and six weeks postpartum. The findings revealed a significant postpartum shift toward a more diverse microbial community, particularly in microbiomes dominated by Lactobacillus iners. However, in women whose vaginal microbiome was primarily composed of Lactobacillus crispatus, L. gasseri, and L. jensenii, changes were observed but were not statistically significant, indicating that these microbiome types were the most resilient to undesirable shifts (3).

References:

1. Wira CR, Rodriguez-Garcia M, Patel MV. The role of sex hormones in immune protection of the female reproductive tract. Nat Rev Immunol. 2015 Apr;15(4):217-30. 
2. Romero R, Hassan SS, Gajer P, Tarca AL, Fadrosh DW, Nikita L, Galuppi M, Lamont RF, Chaemsaithong P, Miranda J, Chaiworapongsa T, Ravel J. The composition and stability of the vaginal microbiota of normal pregnant women is different from that of non-pregnant women. Microbiome. 2014 Feb 3;2(1):4. 
   
3. MacIntyre DA, Chandiramani M, Lee YS, Kindinger L, Smith A, Angelopoulos N, Lehne B, Arulkumaran S, Brown R, Teoh TG, Holmes E, Nicoholson JK, Marchesi JR, Bennett PR. The vaginal microbiome during pregnancy and the postpartum period in a European population. Sci Rep. 2015 Mar 11;5:8988.