Correlation of macroscopic and microscopic placental lesions with obstetric and neonatal outcomes in an unselected population

Many abnormalities of the placenta are reported to be significant in the setting of maternal health problems and adverse fetal/neonatal outcomes. In specific clinicopathological circumstances - eg vascular lesions in the growth restricted fetus – correlation does exist between the placental lesion and the clinical event. Relationships between “lower grade” placental lesions and clinical outcomes are less clear. Reports of associations between selected abnormalities and clinical outcomes are largely based on retrospective case control studies: the clinical groups studied tend to be high-risk. Understanding of the significance of these lesions in the wider population is lacking. This study reports on the clinical events and placental lesions documented in 1119 unselected women delivering at the conclusion of a singleton pregnancy in a single obstetric centre. Study methodology was such that the cohort comprised low-risk mothers delivering at or close to term. The incidence of potentially adverse obstetric and neonatal events in the study population was low. 97% delivered at term. Mean birth weight was 3485 g; mean Apgar scores were 9 at 1 minute and 10 at 5 minutes. 5.9% of infants required admission to neonatal intensive care. When classified in accordance with current standard reporting guidelines, 71% of placentas were classified as normal. Inclusion of lower grade histological lesions in the reporting schedule reduced the percentage of histologically normal placentas to 58%. Funisitis was found to be significantly correlated with adverse neonatal outcome. A number of other placental lesions - including cord coiling <10th and >90th centiles, placental infarction, villitis of unknown etiology and lower grades of acute placental inflammation - were not found to be associated with adverse obstetric or neonatal events. It is concluded that a number of placental lesions may not be relevant to adverse pregnancy outcomes in a low-risk population.