A. Normally adapted maternal spiral arteries with trophoblasts within the vessel lumen and invading the wall, seen at the end of the second trimester (hematoxylin and eosin, ×10). B. A vessel with failed adaptation, with retained smooth muscle, seen near term (hematoxylin and eosin, ×10). C. Acute atheroma with intimal and medial proliferation, fibrinoid necrosis, foamy macrophages, and increased numbers of lymphocytes (“chronic vasculitis”) from an early third-trimester placenta from a woman with pregnancy-induced hypertension (hematoxylin and eosin, ×20).