Characteristics of histopathological and ultrastructural features of placental villi in pregnant Nepalese women

Abstract

The placenta is an important functional unit for gas transfer between mother and fetus. The placental membrane, consisting of trophoblast layer interposed between maternal and fetal blood, plays an active role for intensity of respiration, but no morphological evidence has been documented. Until now, it has been reported that fetal growth retardation and increased fetal mortality rate usually could be seen at high altitude. In an attempt to find the cause of high perinatal mortality rate in Nepal, this study was undertaken to examine pathologically about 1000 Himalayan placentas obtained in Nepal and Tibet since 1977, and the results were compared with those of 5500 Japanese placentas at Saitama Medical School since 1990. In this study, characteristics of ultrastructural features of the Nepalese placental villi investigated in recent years are reported. (1) The gross characteristics of placental pathology in the Himalayan group were represented by marked subchorionic fibrin deposits and increased chorionic cysts in contrast to low incidence of intervillous thrombosis compared with those of the Japanese group. (2) As characteristics of histological findings of the placental villi between Himalayan and Japanese groups, the incidence of chorangiosis and chorangioma in the Himalayan group was significantly higher than that in the Japanese group. (3) Accompanying an increase of vasculosyncytial membrane (VSM) in the villi, thickness and separation of basement membrane of the syncytium in addition to increased apoptosis of syncytial cell nuclei were recognized. (4) As characteristic ultrastructural features of chorionic villi of Nepalese placentas, an increase of mitochondria and cystic formation of rough endoplasmic reticulum (rER), in addition to appearance of lamellar bodies similar to alveolar epithelial type II cell in organellae of the syncytium, were observed. These ultrastructural changes of the placental villous capillaries may be ascribed to hypervascularization caused by the chronic hypoxic state. It is, therefore, presumed that trophoblast cells may play an important role for gas transfer mechanism under such a hypoxic state at high altitude.

Chorangiosis of Chorionic Villi: What Does It Really Mean?

“…13 Villous hypervascularity may then be an adaptive change, as in pregnancy at high altitudes and fetal growth restriction. 5,18,19,39 Some authors conclude that vascular dilatation rather than proliferation is an adaptive change to chronic hypoxia. 32 The author regards this opinion as a moot point because even if villous capillaries are frequently congested in villous hypervascularity (Figure 1), their numbers of lumens are indeed increased as a result of branching angiogenesis.…”

“…7,8 It has been related to several chronic obstetric complications and outcomes, 4 to mention only perinatal deaths, maternal diabetes mellitus, chronic infection, in utero asphyxia, umbilical cord problems, congenital anomalies, fetal vascular thrombosis, maternal anemia, smoking, air pollution, and multiple pregnancy. 7,[9][10][11][12][13][14][15][16][17][18][19][20] The incidence of chorangiosis is low in the second trimester and increases in the third trimester, 21 in which it is lower in preterm than in term pregnancies. 22 Chorangiosis has statistically nonsignificantly clustered with preuterine hypoxia, multiple pregnancy, and normoblasts in fetal circulation.…”

Placental Chorangiosis: The Association with Oxidative Stress and Angiogenesis

“…Many studies have supported the role of maternal hypoxia; pregnancy at high altitude was reported to be associated with maternal hypoxemic hypoxia with resultant intervillous blood hypoxia [47]. Also, it has been reported that chorangiosis is more common in higher altitude gestation placentas with an increasing number of capillary vessels [37,50]. Therefore, a chronic hypoxic stimulus may lead to villous hypervascularity and connective tissue proliferation, with a predominant increase in number rather than in size of capillaries, possibly in order to increase oxygen delivery to the fetus [37,47].…”

Hypoxic Patterns of Placental Injury: A Review

“…21,39 The pattern is evoked by maternal hypoxemia secondary to decreased oxygen pressure in the environment (pregnancies at high altitudes), decreased oxygen binding capacity of the maternal blood (maternal anemia), air pollution and maternal smoking, increased distension of the uterus (multiple pregnancy), and maternal diabetes mellitus (abnormal oxygen-hemoglobin dissociation curve). 21,[38][39][40][41][42][43][44] Clusters of multinucleate giant cells in the decidua basalis and excessive numbers of extravillous trophoblasts are less commonly seen in this than in other patterns of diffuse hypoxic placental injury, 21 most likely because of the association of PR with deep trophoblastic, myometrial invasion, which was proven, at least in maternal anemia. 45 This pattern has a better prognosis than other types of chronic hypoxic injury, 21 probably because of hypoxic preconditioning and resistance to ischemia-reperfusion injury during labor, as was proven in pregnancies at high altitudes 46 and multiple pregnancies.…”