Normal and abnormal transformation of the spiral arteries during pregnancy

Abstract

This article reviews the anatomy and physiology of the uterine circulation, with emphasis on the remodeling of spiral arteries during normal pregnancy, and the timing and anatomical pathways of trophoblast invasion of the spiral arteries. We review the definitions of the placental bed and basal plate of the placenta, their relevance to the study of the physiologic transformation of the spiral arteries, as well as the methods to obtain and examine placental bed biopsy specimens. We also examine the role of the extravillous trophoblast in normal and abnormal pregnancies, and the criteria used to diagnose failure of physiologic transformation of the spiral arteries. Finally, we comment on the use of uterine artery Doppler velocimetry as a surrogate marker of chronic uteroplacental ischemia.

Figure 1.. Microscopic demonstration of physiologic transformation of myometrial segement of the spiral artery in normal pregnancy at term.

Placental bed biopsy specimen was immunostained for cytokeratin-7 to locate trophoblasts (arrowheads) infiltrating the arterial wall, and additional Periodic Acid Schiff (PAS) staining was performed to identify fibrinoid (arrows). Spiral arterial lumen is dilated, and fibrinoid replaces the media and intima. L: spiral arterial lumen (Cytokeratin 7-PAS staining, X100).

Figure 2.. Intravasation (Figure 2A) and extravasation (Figure 2B) routes trophoblast invasion.

Reproduced with permission from Kaufmann P et al. Biology of Reproduction 2003; 69: 1–7.

Figure 2.. Intravasation (Figure 2A) and extravasation (Figure 2B) routes trophoblast invasion.

Reproduced with permission from Kaufmann P et al. Biology of Reproduction 2003; 69: 1–7.

Figure 3.. Microscopic feature of fetomaternal junction (basal plate and placental bed) showing the distal end of the spiral artery (arrows) emptying into the intervillous space (IVS).

Inset shows a longitudinally running spiral arterial segment at a lower magnification. BP: basal plate, CV: chorionic villi, M: myometrium (Cytokeratin 7-PAS, X40 and X100).

Figure 4.. Atherosis of spiral arteries and decidual arterioles in the basal plate (A) and decidua of the fetal membrane (B), respectively.

Arrows indicate vessels affected by atherosis. The hallmark of atherosis is fibrinoid necrosis of the wall (arrows) and the presence of lipid-laden macrophages. (H&E, A: X40, B: X100)

Figure 5.. Comparison of transformed and non-transformed spiral arteries in the myometrium.

Contours of the two arteries are in stark contrast. (A) A transformed spiral artery is characterized by the presence of intramural trophoblasts (arrowheads) and fibrinoid degeneration (arrows) of the wall. (B) Absence of intramural trophoblasts, fibrinoid degeneration, and intact arterial contour mark spiral artery with failure of physiologic transformation (Cytokeratin 7-PAS, X200).