Rationale
Variations within the vaginal microbiome have been associated with
higher risk preterm birth and other pregnancy complications such as
chorioamnionitis. Microbes associated with these complications such asStreptococcus agalactiae and Gardnerella vaginalis, are
frequently present in polymicrobial as well as Lactobacillus predominant
vagial microbiomes.1 In light of these considerations,
a growing body of research has focused on characterizing the vaginal
microbiome using metagenomic approaches. Among the most common
methodologies are those that rely on universal targets, 16S ribosomal
RNA and cpn60 genes, allowing for more detailed taxonomic classification
and profiling of the vaginal microbiome during pregnancy than culture
based or targeted methods. However, data from amplicon-based metagenomic
characterizations suggest that such methods provide an incomplete
understanding of the species-level diversity present in the vaginal
microbiome.2 For example, there is a notable lack of
discussion of S. agalatiae , commonly referred to as Group B
Streptococcus (GBS), a known pathogen associated with poor maternal,
fetal, and neonatal outcomes in amplicon-based metagenomic vaginal
microbiome studies during pregnancy.
Currently, in the United States, screening for GBS occurs at 36 to 38
gestational weeks,3 with those who test positive
receiving antibiotic treatment during labor to help prevent early-onset
GBS. Previous data indicate that approximately one in four women is
colonized by GBS (Centers for Disease Control and Prevention). Yet,
apart from this routine clinical screening near the time of birth, there
are limited metagenomic studies that identify or evaluate GBS during
pregnancy. While screening for GBS prior to birth has reduced early
onset neonatal sepsis caused by GBS in the U.S.,4 the
transient nature of maternal GBS colonization is not well
understood.5,6 Improved understanding of the dynamics
of maternal GBS colinzation during pregnancy can provide additional
insights for preventing GBS complications affecting maternal and fetal
health throughout pregnancy and birth (e.g., miscarriage and
stillbirth).