We are pleased to continue our new series here on the Evolving Women's Health blog with Chief Science Officer Elizabeth DuPriest, Ph.D.
Q: How can the biome affect fertility and pregnancy?
The vaginal microbiome is in fact strongly related to fertility and pregnancy, with the healthiest vaginal microbiomes (those dominated by Lactobacillus crispatus, L. gasseri, or L. jensenii) typically associated with the best outcomes.
Let’s start with fertility. Most of what is known is based on women undergoing in vitro fertilization (IVF) simply because it is logistically easier to do than to study fertility and the microbiome in the general population. For example, Babu et al (2017) showed that women with infertility had lower levels of lactobacilli and higher levels of Candida, Enterococcus, and E. coli. Campisciano et al (2017) showed women with idiopathic infertility had lower lactobacilli levels than women with known causes of infertility, and suggested that women with repeated IVF failure should be screened for dysbiosis.
For those closely watching the literature, you might have noticed a couple studies showing worse IVF outcomes for women with L. crispatus, and it might have made you wonder. We believe this is a selection-bias issue. In other words, women with L. crispatus don’t end up at a fertility clinic because of their biome. They have something more significant preventing them from becoming pregnant; whereas women with a poor biome may have infertility that is based primarily on their biome, which may be easier to overcome through IVF. And of course, bacterial vaginosis (BV) increases risk of pelvic inflammatory disease (PID), which can cause tubal infertility or other structural issues. But it’s not only about being able to get pregnant: BV is also tragically associated with increased rates of miscarriage, both in the first trimester and later in pregnancy.
In addition to difficulties becoming or remaining pregnant, the vaginal microbiome is associated with increased risk of adverse pregnancy outcomes. BV has been linked to premature rupture of membranes, whether at term or preterm, which can allow quickly ascending infection. BV has been strongly linked to preterm birth and also associated with having a low birthweight (or small-for-gestational-age) baby. BV is also linked to maternal infections (chorioamnionitis, endometritis) and to neonatal infections. Women with Group B Strep (“GBS”, or Streptococcus agalactiae), whether symptomatic or asymptomatic, are known to be at risk for their babies developing a neonatal strep infection, which can cause sepsis and meningitis, sometimes leading to death.
In the past, it was thought that lactobacilli levels increased during pregnancy due to increasing estrogen levels. Now, data show that this is true only for women starting pregnancy with a healthy vaginal microbiome. Those who have an intermediate biome, dominated by L. iners, have been shown to deteriorate into a BV-like biome during pregnancy. Therefore, starting a fertility journey with a healthy microbiome gives the best chance for a healthy mom and baby.