Unilateral thickening of placental fetal veins

Unilateral muscular thickening (ULT) was observed in the wall of the fetal veins on the placental surface beneath the amnion. The maternal facing wall of the fetal veins was thin, and protruded into the amniotic sac. The ratio of the thickness of the maternal facing to the fetal facing wall was 4:1 to 3:1 in the fetal veins. ULT was found to develop after 17 weeks of gestation and was not observed in the small veins less than 1.0 mm in diameter or in the veins located in the deep portion of the chorionic plate. The intimal thickening was not recognized and there was no lipid deposition in ULT. ULT was found in every one of 110 mature placentae and was assumed to be a normal histological finding.