The Maternal Microbiome in Pregnancy: From Physiological Changes to Dysbiosis and Obstetrical Complications—Therapeutic Perspectives

During pregnancy, hormonal, metabolic, and immunological changes influence the composition and function of maternal microbial communities. Increasing evidence suggests that the maternal microbiota—particularly in the vaginal, gut, and oral environments—plays a significant role in maintaining pregnancy homeostasis and supporting fetal development. In healthy pregnancies, the vaginal microbiota is typically dominated by Lactobacillus species, which help maintain a low vaginal pH and protect against ascending infections. However, disruption of this balance (vaginal dysbiosis) has been associated with obstetrical complications such as intrauterine infection and preterm birth. Similarly, the maternal gut microbiota undergoes trimester-specific changes that contribute to metabolic adaptations required for fetal growth, while alterations in microbial composition have been linked to metabolic disorders including gestational diabetes mellitus and preeclampsia. Changes in oral microbiota and periodontal disease have also been associated with adverse pregnancy outcomes through systemic inflammatory pathways and potential microbial translocation to the placenta. Recent advances in sequencing technologies have improved the understanding of host–microbiome interactions in pregnancy, although the existence of a placental microbiome remains controversial. Overall, maternal microbiota plays an important role in pregnancy physiology, and its dysregulation may contribute to obstetrical complications. Understanding these mechanisms may facilitate the development of microbiome-based diagnostic and therapeutic strategies in maternal–fetal medicine.