Defining normal placental histology: histopathologic findings and interobserver reproducibility in clinically uncomplicated term pregnancies

Abstract

Introduction

The Amsterdam consensus criteria have standardized placental lesion classification; however, the histopathologic spectrum of clinically uncomplicated pregnancies and the reproducibility of placental assessment remain incompletely defined. We aimed to characterize histopathologic findings in term placentas from uncomplicated pregnancies with favorable outcomes and assess interobserver reproducibility.

Methods

In this multi-rater observational study, 35 placentas from physiologic term singleton pregnancies were evaluated by 14 perinatal pathologists. Three full-thickness sections per case were digitized at ×40 magnification and independently assessed. Twenty-seven variables encompassed Amsterdam-defined lesion categories, findings often associated with adverse pregnancy outcomes, and morphologic characteristics of uncertain clinical significance. Interobserver agreement was assessed using intraclass correlation coefficients and Krippendorff's alpha.

Results

Findings from all three categories occurred in placentas with favorable outcomes. Agreement was low for villous maturation (α = 0.129), fetal vascular malperfusion (α = 0.161), chorangiosis (α = 0.178), and syncytial knotting (α = 0.181), while maternal vascular malperfusion showed minimal reproducibility (α = 0.016). Giant multinucleated extravillous trophoblast cell counts showed the highest reproducibility (ICC = 0.633).

Discussion

Placental histopathologic findings in uncomplicated pregnancies vary in standardization, clinical relevance, and reproducibility. Consensus-defined lesions may require refined operational thresholds, findings often associated with adverse outcomes require attention to extent and distribution, and morphologic characteristics of uncertain clinical significance require outcome-based validation. These findings support contextual interpretation and continued refinement of diagnostic criteria and normal placental morphology.