Non-thrombotic changes of fetal placental vessels in stillbirths. A qualitative and quantitative study.

A qualitative and quantitative microscopical examination of fetal stem vessels was performed in 50 placentas of stillborn infants and 50 normal controls. The vascular changes were morphologically similar in both groups, differences being only of quantitative nature. Subendothelial edema was more frequent in control placentas suggesting that it is not pathological. Subendothelial proliferation of smooth muscle cells prevailed in control and fresh stillbirths and could be due to arterial growth. Subendothelial proliferation of undifferentiated cells or fibrous and muscular tissues was more common in stillbirths. It occurred in most placentas of macerated stillbirths, but in fresh stillbirths the frequency was lower, though significantly higher than in controls. This thickening could represent the only reaction of placental vessels to fetal or maternal disease or cessation of fetal blood flow. Occlusion of the vascular lumen by fibrous and muscular tissues and vascular lumen divided by septa were present in the majority of the placentas of macerated stillbirths and rarely in fresh stillbirths, suggesting that in the macerated ones these changes were secondary to placental retention. The progressive collagenization of the media was the alteration most closely related to time of placental retention.