Gestational Age-Dependent Associations Between Mycoplasma/Ureaplasma Colonization and Inflammatory Placental Lesions in Preterm Birth

Background: Infection and inflammation are key contributors to spontaneous preterm birth (PTB), but the relationship between genitourinary microbial colonization and placental inflammatory pathology across preterm subgroups remains unclear. Methods: In this case–control study, women with PTB were compared with gestational age-matched controls. Urine cultures, Mycoplasma/Ureaplasma screening, inflammatory markers, and placental histopathology were analyzed. Early (24–33 weeks) and late (34–36 weeks) preterm births were evaluated separately. Results: Clinical risk factors were more common in PTB cases (87.0% vs. 68.7%, p = 0.001), particularly PPROM and fetal growth restriction. Conventional urine culture positivity did not differ between groups. Mycoplasma/Ureaplasma colonization was more frequent in controls (41.2% vs. 15.4%, p < 0.001). Early PTB was strongly associated with placental inflammation, including higher rates of histological chorioamnionitis, composite inflammatory lesions, placental culture positivity, and elevated CRP compared with late PTB. Conclusions: Early PTB may represent a distinct infection-associated phenotype characterized by prominent placental inflammation, whereas late PTB demonstrates a weaker inflammatory profile.