Placental histopathology associated with pre-eclampsia: systematic review and meta-analysis

Pre-eclampsia (PE) is associated with impaired trophoblastic invasion and typical villous and vascular placental lesions. The primary aim of this study was to quantify the prevalence of placental histopathological lesions in pregnancies complicated by PE.

MEDLINE, EMBASE and CINAHL were searched electronically, and relevant articles reporting on placental histopathological lesions were assessed according to the following criteria: study design, number of pregnancies included, severity of PE and whether the pathologist was blinded to the clinical information. Prospective and retrospective case-control studies including ≥ 100 pregnancies were included in the systematic review. The incidence of each type of histological lesion according to the Perinatal Section of the Society for Pediatric Pathology classification in pre-eclamptic and normal pregnancies was identified, and lesions were categorized into two main groups: villous lesions and vascular lesions. Random-effects meta-analysis of proportions was used for analysis. Between-study heterogeneity was assessed using the I² statistic.

The search yielded 717 citations, and a total of eight studies (four blinded and four non-blinded) were included in the review. In unblinded studies, the pooled prevalence of villous lesions was 11.6% and 48.2% in normal and pre-eclamptic pregnancies, respectively, giving a pooled odds ratio (OR) of 7.59. In blinded studies, the pooled prevalence of villous lesions was 18.5% and 42.0% in normal and pre-eclamptic pregnancies, respectively, giving a pooled OR of 4.28. In unblinded studies, the pooled prevalence of vascular lesions was 8.1% and 37.3% in normal and pre-eclamptic pregnancies, respectively, giving a pooled OR of 20.34. In blinded studies, the pooled prevalence of vascular lesions was 9.8% and 38.9%, in normal and pre-eclamptic pregnancies, respectively, giving a pooled OR of 7.08.

In blinded studies, the incidence of both placental villous and vascular histopathological lesions is four- to seven-fold higher in pre-eclamptic than in normal pregnancies. Greater differences are reported in unblinded studies. Despite the higher probability (point prevalence) of finding abnormal placental pathology in pregnancies with PE, placental lesions are not specific to the diagnosis of PE. Copyright © 2017 ISUOG. Published by John Wiley & Sons Ltd.