Trophoblast alterations in the placental bed in relation to physiological changes in spiral arteries.

Ninety-three placental bed biopsies containing a segment of a spiral artery at the level of the decidual-myometrial junction (53 with and 40 without physiological changes) were histologically investigated for depth of trophoblastic penetration of the uterine wall, formation of trophoblastic multinucleated giant cells and the enzyme histochemical characteristics of the interstitial (stromal) and vascular (intramural) trophoblast. The depth of trophoblastic penetration was not related to the presence or absence of the physiological changes. Conversely, in the absence of physiological changes, a significant accumulation of multinucleated giant cells at the decidual-myometrial junction was found before 36 weeks of gestation. The enzyme histochemical characteristics of the placental bed trophoblast suggest a stromal migration of trophoblast to the proximal (decidual-myometrial) part of the spiral artery whereas the distal part might be invaded by intraluminal (upstream) invasion. The hypothesis is put forward that in the absence of physiological changes a disturbed stromal migration is caused by intrinsic (trophoblastic) or extrinsic (interstitial of vascular) factors expressed by the augmentation of the multinucleated cells at the decidual-myometrial junction.