Introduction: Placental examination is valuable for diagnosing congenital syphilis, but the classic histological triad is not always observed. This study aimed to identify additional morphological clues, evaluate the sensitivity of IHC and qPCR, and investigate the impact of HIV co-infection and penicillin treatment on placental morphology. Materials and methods: Two hundred and fifteen placental specimens with treponemal infection were reviewed. Morphological findings, IHC, and qPCR results were analyzed. Results: Chronic villitis (94%), acute chorioamnionitis (91.6%), and villous immaturity (65.6%) were the most common abnormalities. HIV co-infection and penicillin treatment were associated with reduced frequencies of inflammatory lesions. IHC and qPCR exhibited sensitivities of 74.4 and 25.8%, respectively, confirming the diagnosis in 42 cases with negative or unknown serology. Conclusion: Villitis, chorioamnionitis, and villous immaturity were identified as the predominant placental abnormalities. HIV co-infection and penicillin treatment can impact morphology and hamper the diagnosis. IHC and q-PCR are valuable adjuncts when serology is negative.
Keywords: HIV; Placenta; Treponema pallidum PCR; Treponema pallidum immunohistochemistry; syphilis.