Immunohistochemical Identification of Placental Bed Biopsies and the Implications for the Inclusion of Specimens when Studying the Spiral Artery Response to Pregnancy

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Abstract
Objectives: To determine if a cytokeratin marker facilitates the detection of trophoblast and refines the identification of placental bed biopsies compared to standard techniques. Methods: Placental bed biopsies, n = 320, were taken at caesarean section from 148 women. Using standard histology, tissue sections were examined under light microscopy for trophoblast. Morphological features of spiral arteries were recorded. Biopsies in which no trophoblast was identified were stained for cytokeratin and reexamined under light microscopy. Results: In 148 (48%) of the biopsies, trophoblast was not identified using standard methods. Eighty-nine of these were stained for cytokeratin and 35 (39%) were found to contain trophoblast. In the placental bed, extravillous trophoblast distribution is not uniform, the morphology is diverse, giant cells are not predominant, and glandular tissue is often abundant although attenuated. Spiral artery morphology can be variable in the same biopsy. Conclusions: The identification of the placental bed can be improved and refined using a cytokeratin marker. Many positive biopsies may be overlooked using standard techniques. Criteria used in the past for including a biopsy when studying spiral arteries need modification.