Oral, Vaginal, and Placental Microbiota Profiles in Japanese Pregnancies with Preterm Birth and Chronic Abruption-Oligohydramnios Sequence (CAOS): A Cross-Sectional Study

<i>Background and Objectives</i>: Preterm birth (PTB) imposes a substantial medical and economic burden on perinatal care. Recent advances in 16S rRNA gene sequencing help detailed microbiota analysis. Understanding microbiota's contribution may help in understanding PTB pathogenesis. We aim to investigate the microbiota profiles of the oral, vaginal, and placental microbiota in pregnant Japanese women hospitalized for care of preterm labor and examine the association between them and perinatal outcomes. <i>Materials and Methods</i>: This cross-sectional study included 20 pregnant Japanese women admitted to a single perinatal center for preterm labor between 2022 and 2023. Oral, vaginal, and placental samples were collected aseptically during hospitalization. The patients were retrospectively categorized into: term birth (TB, <i>n</i> = 10), chronic abruption-oligohydramnios sequence (CAOS, <i>n</i> = 3), and PTB without CAOS (PTB, <i>n</i> = 7) perinatal outcomes. Microbiota profiles were analyzed using 16S rRNA gene sequencing, and group comparisons were performed using univariate statistical methods. <i>Results</i>: Alpha or beta diversity of the oral and vaginal microbiota among the three groups did not differ significantly. CAOS and PTB groups showed a trend toward altered vaginal microbial composition, but not the TB group. In the placental microbiota, beta diversity differed significantly among the TB, PTB, and CAOS groups. <i>Ureaplasma urealyticum</i> was more abundant in the PTB group, whereas <i>Ureaplasma parvum</i> was more abundant in the CAOS group. <i>Conclusions</i>: A potential shift in the vaginal microbiota and alterations in the placental microbiota, observed in PTB, including CAOS, suggested a possible microbial contribution.