A 2021 study published in the peer-reviewed medical journal Reproductive Sciences examined the vaginal microbiome compositions of 48 women during pregnancy and postpartum to understand changes in host physiology between these two time periods. Researchers found significant vaginal microbiome differences, with an increase in diverse taxa immediately following pregnancy among the women.
Of the 48 women enrolled in the study, 32 completed vaginal samples during the first and third trimesters, and following 28-45 days postpartum. It is noted that all of the women had vaginal deliveries. To determine the vaginal community composition, researchers identified 358 total taxa which were used to analyze the abundance of taxa and alpha-diversity (the species diversity within a community at a local site). All of the women also had vaginal pH measurements less than 4.5 which is within an optimal vaginal pH range.
Interestingly, researchers found a significant difference between the two vaginal biome composition periods: a high dominance of Lactobacillus species–the dominant species which produces antimicrobial compounds and characterizes a healthy vaginal biome–were identified in the first and third trimester. However, in the postpartum period, vaginal biome compositions measured low proportions of Lactobacillus and a diverse array of bacteria, including G. vaginalis, Prevotella spp., and Streptococcus spp., among other bacterium.
Lactobacillus are the predominant species that make up a healthy vaginal microbiome. In the study L. crispatus, L. jensenii, and L.gasseri (although not L. iners) were significantly lower in abundance in the women postpartum. In addition, decreased levels of D- and L-lactic acid and increased levels of hyaluronan and Hsp70 were found. Abundance of Lactobacillus is positively associated with estrogen production, so decreased Lactobacillus levels may be explained by the decreased levels of estrogen (estradiol and estriol) commonly seen post-delivery. While researchers were uncertain how much estrogen levels change overall in the postpartum period, they noted that “if there is a lag time for estrogen levels to rebound after birth, this could lead to lower abundances of lactobacilli in vaginal communities for quite some time post-delivery.”
Researchers noted that lower Lactobacillus and lactic acid levels may lead to reduced vaginal acidification (a healthy vaginal pH) which may in turn lead to an increase in non-lactobacilli proliferation and an increase in alpha-diversity. Monitoring the vaginal biome composition postpartum and applying Lactobacillus therapy in the form of probiotics and natural lactic acid may support the restoration of vaginal biome composition. Furthermore, the authors mentioned that “the vaginal microbiota are consequences of alterations in nutrient availability, vaginal pH, and local immune parameters that change the ability of different bacterial species to survive and proliferate,” noting that different factors can influence and affect vaginal flora.
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Kenetta L. Nunn, Steven S. Witkin, G. Maria Schneider, Allison Boester, Dimitrios Nasioudis, Evelyn Minis, Karol Gliniewicz, and Larry J. Forney
Reproductive Sciences, July 2021
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