Vaginal microbiome and its implications in preterm birth

Preterm birth (PTB), defined as birth occurring before 37 weeks of gestation, remains a major global public health challenge, affecting approximately 10% of pregnancies worldwide and contributing significantly to neonatal morbidity and mortality. Despite extensive research, the etiology of PTB is multifactorial and not yet fully understood, with ongoing debates regarding the contributions of inflammation, hormonal dysregulation, genetic predisposition, and environmental factors such as microbial dysbiosis. Recent studies have highlighted the role of the vaginal microbiome in pregnancy outcomes, particularly its association with PTB. This review consolidates current findings on the vaginal microbiome's influence on PTB, addressing microbial dysbiosis as a key risk factor. Despite differences in ethnicity, gestational age at sample collection, and analytical methodologies, a common observation is that a decrease in Lactobacillus species is associated with an increased risk of PTB. These differences influence study outcomes by affecting variations in microbial composition, host immune regulation, genetic predisposition, and environmental influences. However, a consistently observed trend is that a Lactobacillus-dominant vaginal microbiome is generally associated with a lower risk of PTB across diverse populations. This review also discusses the limitations of existing research and suggests directions for future microbiome studies.