A study of placental bed spiral arteries and trophoblast invasion in normal and severe pre-eclamptic pregnancies.

OBJECTIVE: To investigate trophoblast invasion and vascular changes in placental bed spiral arteries in normal and severe pre-eclamptic pregnancies.

DESIGN: A histological and immunohistochemical study of placental bed biopsies containing spiral arteries.

SETTING: The University Hospital, Leuven, Belgium.

SUBJECTS: Twenty-one placental bed biopsies from 21 normal pregnancies and 24 placental bed biopsies from 24 severe pre-eclamptic pregnancies, taken at caesarean section.

OBSERVATIONS: Histological and immunohistochemical appearance of spiral arteries (stained with haematoxylin and eosin), periodic acid schiff, and a monoclonal antibody to low molecular weight cytokeratin.

RESULTS: One hundred and twenty-seven spiral arteries were studied. In the 21 biopsies from clinically normal pregnancies at term, 100% of the decidual spiral arteries and 76% of the myometrial arteries showed trophoblast invasion. In the 24 biopsies from women with severe pre-eclampsia, trophoblast invasion was seen in 44% and 18% of the decidual and myometrial segments, respectively. Endovascular trophoblast invasion was complete, partial or isolated. A variety of morphological features was present not only in different spiral arteries from the same biopsy but also in different segments of the same artery. The vascular change most commonly associated with normal pregnancies was physiological change and subintimal thickening of both segments of the spiral arteries. In pre-eclampsia medial disorganisation and hyperplasia in the myometrial arteries and acute atherosis in decidual arteries were common.

CONCLUSION: Endovascular trophoblast did not show an all or none invasive phenomenon in normal and pre-eclamptic pregnancies. More decidual than myometrial arteries were invaded in both groups of patients, and there was a gradient in the percentage of decidual and myometrial arteries invaded from normal pregnancy to pre-eclampsia. Morphological features in one spiral artery may not necessarily be representative of all of those in a placental bed.