Clinicopathological significance of amniotic papillary folding in the fetal membrane of the placenta: A single-institution study.

Amniotic lesions provide useful information regarding the conditions of the fetus and mother in the gestational period. We noticed a characteristic papillary, branching or ramifying structure of the amnion on the fetal membrane that we termed "amniotic papillary folding" (APF), which was identifiable on microscopic observation, but not macroscopically. Based on the morphological features, APF entirely comprises preexisting amnion and seems to result from misalignment of the amnion. Among 201 placentas submitted for histopathological examination, 88 placentas (43.8 %) displayed APF. From a clinical perspective, APF appeared more frequently in placentas from mothers with hypertensive disorders of pregnancy (HDP). Conversely, APF was significantly less frequent in mothers with gestational diabetes mellitus (GDM). APF tended to be infrequent among mothers with threatened miscarriage, non-reassuring fetal status (NRFS) or fetal growth restriction (FGR). Regarding the relevance to other pathological diagnoses, chorioamnionitis was significantly associated with a reduced frequency of APF, whereas placental infarction was associated with an increased frequency. Our results may imply that the histogenesis of APF is positively associated with retained activity of the fetus in the uterus. APF might be infrequently encountered under conditions in which the fetus is weakened with attenuated mobility, including threatened miscarriage, NRFS, FGR, and most prominently GDM. Although the mechanisms involved remain unclear, this unique amniotic structure may offer a marker for the status of fetal dynamics and abnormal maternal conditions.