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).