Morphology of fetal placental stem arteries in hypertensive disorders ('toxemia') of pregnancy.

Morphological features of 3rd order, fetal stem arteries of placentae from 50 'toxemic' patients, including all types, i.e., those with pre-eclampsia, essential hypertension, and chronic renal disease, were compared with similar arteries in 50 placentae of normal pregnancies. Striking changes of the arterial wall and subtle but definite alterations in the surrounding stroma were observed in the fetal arteries from hypertensive pregnancies. The earliest mural alteration consisted of endothelial proliferation which narrowed the lumen. This was followed by proliferation of subendothelial and smooth muscle cells probably derived from the medial layer. In the media, the proliferating smooth muscle cells were affected by vacuolation and other degenerative processes. Of the above changes the intimal and medial alterations were present in 38 placentae of toxemic patients, whereas some of these features were found only in 6 cases of the control group. Other lesions of the fetal stem arteries (i.e. thrombi and arteritis) were observed less commonly. Moreover, smooth muscle cells that usually are scattered in the villous stroma in normal placentae, in toxemic patients were more numerous and tended to form bridges between the fetal arteries. On the basis of the present observations, it may be concluded that several lumen-narrowing alterations affect the fetal arteries of the placentae in toxemia of pregnancy. Whereas these undoubtedly contribute to the 'placental insufficiency' commonly found in this group of diseases, they probably represent a reaction to a more basic and as yet not identified factor(s) that may be operational in 'toxemia' of pregnancy.