An immunohistologic study of endothelialization of uteroplacental vessels in human pregnancy--evidence that endothelium is focally disrupted by trophoblast in preeclampsia.

OBJECTIVE: Our objective was to study the endothelial status of the luminal lining of uteroplacental vessels in the human placental bed in normal and abnormal pregnancy in the third trimester. STUDY DESIGN: Six placental basal plates from uncomplicated pregnancies and five from pregnancies complicated by preeclampsia (n = 3), preeclampsia and a small-for-gestational-age infant (n = 1), and diabetes mellitus (n = 1) were accessioned from the archives because of documentation of their containing uteroplacental vessels. Five placental bed biopsy specimens with intraluminal endovascular trophoblast in the third trimester were also studied. Sections were subjected to immunohistochemical analysis with monoclonal and polyclonal antibodies labeling endothelium and trophoblast. RESULTS: In third-trimester normal uncomplicated pregnancies the uteroplacental arteries and veins were completely endothelialized with no disruption of the endothelium. In third-trimester abnormal pregnancies the uteroplacental veins were also completely endothelialized. However, intraluminal endovascular trophoblast was seen within the uteroplacental arteries in eight of the 10 complicated pregnancies; this finding was associated with disruption of the endothelium. CONCLUSION: In preeclampsia there is an aberrant wave of endovascular trophoblast migration in the third trimester, resulting in focal disruption of the endothelium. This may be responsible for the endothelial cell dysfunction thought to be of pathogenetic importance in preeclampsia.