[Effect of rivanol-induced abortion on placental histology: pitfalls in pathological interpretations]

Objective: Placental pathology reflects the health condition of both mother and fetus during pregnancy, providing information about pathogenesis especially in adverse pregnancies, and may provide guidance on subsequent pregnancies. Description on the placental changes after long-term use of rivanol is lacking, and this evaluated the placental changes, with emphasis on the differential diagnosis from other primary placental lesions. Methods: A total of 85 placentas from rivanol induced abortion submitted to the Department of Pathology, Obstetrics and Gynecology Hospital of Fudan University from Januaury 2017 to October 2019 were reviewed; and 81 gestational-age-matched cases of spontaneous abortion or preterm delivery during the same period were also included as the control group. Diagnoses were based on the consensus statement of 2016 Amsterdam Placental Workshop Group. Statistical differences were analyzed by individual diagnostic terms. Results: The maternal age in rivanol group was (30.5±4.1) (range 22-41) years, compared with (30.9±4.3) (range 22-44) years in the control group. Gestational age was (23.2±3.5) (range 17-35) weeks and (23.3±2.8) (range 17-33) weeks in the rivanol and control groups. The incidence of chorioamnionitis in rivanol group was 91.8%, significantly higher than the control (63.0%, P<0.05); and there were more stage 1 (subchorionic) maternal response in rivanol than in the control (61.0% vs.28.6%, P<0.05) groups. In addition, acute deciduitis was also more common in rivanol group (27.1% vs. 13.6%, P<0.05). No significant difference was observed in fetal inflammatory responses (vasculitis of vessels in chorion plate and umbilical cord); maternal malperfusion (narrowing of intervillous space, increased intervillous fibrin deposition, decidual arteriopathy, villous infarction and retroplacental hematoma); and fetal malperfusion (villous stromal hemorrhage and avascular villi). Conclusions: The chemical chorioamnionitis caused by rivanol is characterized by maternal inflammatory response of low stage and high grade. The use of rivanol has no obvious impact on the fetal inflammatory response, maternal malperfusion and fetal malperfusion. Such morphologic changes may reflect the original placental lesions.