Abstract Aim The aim of the present study was to establish the association between the presence of oral and uro‐vaginal microorganisms in the placental membrane and preterm delivery ( PTD ), the premature rupture of membranes ( PRM ), and the clinical signs of intra‐amniotic infection. Methods Eighty‐four women with PTD and 127 women with delivery at term were assessed for the PRM , clinical signs of intra‐amniotic infection, and the presence of periodontitis. Twenty‐seven microorganisms were identified in the placental tissue using nested polymerase chain reaction ( PCR ). Porphyromonas gingivalis ( P. gingivalis ) was quantified by droplet digital PCR . Results The prevalence of microorganisms was 9.47% (20/211). P. gingivalis was the most prevalent (12/211, 5.68%). Mycoplasma hominis , Ureaplasma urealyticum , Staphylococcus spp, and Fusobacterium nucleatum were isolated at a very low frequency in the placenta. Candida albicans was associated with PTD ( P = 0.027). Periodontitis was associated with clinical signs of infection (odds ratio [ OR ] = 3.8, 95% confidence interval [ CI ]: 1.28‐13.5) and with PTD ( OR = 1.99; 95% CI : 1.07‐3.72). Conclusion The presence of P. gingivalis in the placenta was not associated with perinatal complications. Detecting microorganisms in the placenta by nested PCR is not relevant, as it has a poor association with clinical variables that establish the diagnosis of chorioamnionitis. However, periodontitis was associated with the clinical signs of intra‐amniotic infection and PTD .