Pathologic evaluation of normal and perfused term placental tissue

Abstract This study reports for the first time the incidence and interobserver variation of morphological findings in a series of 34 term placentas from pregnancies with normal outcome used for perfusion studies. Histologic evaluation of placental tissue is challenging, especially when it comes to defining "normal tissue" versus "pathological lesions". A scoring system for registration of abnormal morphological findings was developed. Light microscopic examination was performed independently by two pathologists, and inter-observer variation was analysed. Findings in normal and perfused tissue were compared and selected findings were tested against success parameters from the perfusions. Finally, the criteria for frequent lesions with fair to poor interobserver variation in the non-perfused tissue were revised and re-analysed. In the perfused tissue the perfusion artefact "trophoblastic vacuolization", which is believed to represent dilated transtrophoblastic channels, was reproducible and significantly correlated to the perfusion marker "fetal leakage". In longer perfusions, microscopy of the perfused cotelydon revealed bacteria in the fetal vessels. This finding led to an adjustment in the perfusion protocol with addition of antibiotics to the medium. In the "normal" tissue, certain lesions were very frequent and showed only fair or poor interobserver agreement. Revised minimum criteria for these lesions were defined and found reproducible. This study has emphasised the value of pathological examination as a supplement in placental perfusion models. Examination of the perfused cotelydon for trophoblastic vacuolization is recommended as an additional quality marker in perfusion models. The study also underlines the need for exact definitions of abnormality in frequent placental lesions.