François Teasdale

Gestational changes in the functional structure of the human placenta in relation to fetal growth: A morphometric study☆☆☆

The study of different morphometric parameters in 17 placentas collected between 22 and 40 weeks of gestation has shown that, from mid-gestation to term, two stages are clearly discernible in the development of the human placenta. The first stage of growth, which terminates at approximately 36 weeks of gestation, is characterized by a progressive increase in parenchymal components. The second stage, which extends from around 36 weeks to term, is called the maturation stage because it is characterized by substantial fetal growth but without any increase in placental functional tissues. Evidence of this growth in function was also suggested by the demonstration of a sevenfold increase in fetal weight in the last half of pregnancy, despite a twofold decrease in the relative villous surface area. Furthermore, the study has shown that, at a given gestational age, fetuses with relatively small placentas tend to outgrow the functional capacity of their placentas.

Idiopathic intrauterine growth retardation: histomorphometry of the human placenta.

The morphological changes in the functional structure of the placenta in cases of idiopathic intrauterine growth retardation (IUGR) have been investigated with quantitative analyses. It has shown that the placentae of the small-for-gestational-age (SGA) infants were 45 per cent smaller than the controls, due to an almost equal reduction in parenchymal (48 per cent) and non-parenchymal (42 per cent) tissues. Consequently, in relative values the placentae of the SGA infants were shown to be otherwise very similar to the controls. In contrast, in absolute values, the placentae of the growth-retarded infants were shown to differ from the controls by having significantly less surface area of exchange between mother and fetus, mainly in terms of peripheral capillary (3.85 vs 7.21 m2; P less than 0.02) and villous (4.31 vs 8.74 m2; P less than 0.005) surface areas, and intervillous space volume (53.71 vs 103.26 cm3; P less than 0.001). The total number of cells (53 418 x 10(6) vs 104 820 x 10(6); P less than 0.005) was also shown to be markedly decreased in the placentae of the SGA infants, compared with the controls, and the placental membrane showed a 51 per cent decrease in trophoblast mass or cellular content. On a functional basis, these findings suggest that, in these cases of idiopathic IUGR, the placental morphological changes are bound to produce placental insufficiency and fetal growth retardation.

Histomorphometry of the human placenta in maternal preeclampsia

The placentas of five mothers with severe preeclampsia who gave birth to moderately growth-retarded term infants were compared to a group of placentas collected from mothers who had uncomplicated pregnancies and normal term infants who were appropriate for gestational age. This study demonstrated that, on a quantitative histologic basis, the placentas of the preeclamptic mothers were morphologically very similar to the control placentas in terms of weight, parenchymal and cellular content, and surface areas of exchange between mother and fetus. The findings of this study support the hypothesis that, in preeclampsia not associated with severe intrauterine growth retardation, the perinatal morbidity associated with this condition is probably related more to some alterations in uteroplacental and, possibly, umbilical blood flows than to significant changes in placental structure and function. This may be due to compensatory repair mechanisms and extensive functional reserve capacities in these placentas.

Histomorphometry of the human placenta in class C diabetes mellitus

Placentae from Class C diabetic mothers were compared by histomorphometric analyses with a group of normal placentae. The placentae of the diabetics were divided in two groups based on the growth characteristics and neonatal outcome of the infants at birth. This study has demonstrated that the placentae of both groups were somewhat heavier than the controls due to a parallel increase in parenchymal and non-parenchymal tissues. The placentae were also shown to be characterized by a relative increase in the surface areas of exchange between mother and fetus, in terms of peripheral villous and capillary surface areas and intervillous space volume. Consequently, the results of this study suggest that, in Class C diabetics, placental morphology and placental function are probably not more adversely affected than in other less severe forms of the disease during pregnancy. Furthermore, the findings in this investigation support the hypothesis that the placental changes, and the perinatal morbidity associated with this condition, are probably the results of hormonal and metabolic abnormalities present in the mother and the fetus.

Histomorphometry of the placenta of the diabetic woman: Class A diabetes mellitus

Different morphometric parameters have been applied to the study of the morphological differences between a group of normal placentae and a group of placentae collected from Class A diabetic women. It has shown that although fetal weights were significantly higher in the infants of the diabetic mothers, placental weights showed only a tendency to be heavier than the gestationally matched controls, though the difference was not statistically significant. However, the placentae of the Class A diabetic mothers were shown to differ from the control group by having significantly more parenchymal and villous tissues and a higher cellular content. There were also more surface areas of exchange between mother and fetus, in terms of peripheral and villous capillary surface areas and intervillous space volume. On a functional basis, these morphological changes suggest that, in diabetes mellitus Class A, the placenta can efficiently support the growth of a large fetus, and the perinatal associated with this condition is not likely to be related to decreased or insufficient function of the placenta.

Morphometric evaluation of the microvillous surface enlargement factor in the human placenta from mid-gestation to term

The factor by which the villous surface area is enlarged owing to the presence of microvilli has been evaluated with quantitative analyses in human placental tissues from mid-gestation to term. It has shown that, between 25 and 36 weeks of gestation, the peripheral villous surface area is enlarged by a constant factor of approximately 9.47 +/- 0.28 (mean +/- s.d.). Then, from 36 weeks to term, it has shown a significant decrease in the microvillous surface enlargement factor (9.44 to 7.67; P less than 0.01). Consequently, the actual surface area of exchange between mother and fetus was shown to be significantly decreased during that same period (93.91 to 67.02 m2; P less than 0.01). On a functional basis, these findings support the theory that, during that last four weeks of pregnancy, the increasing physiological needs of the fetus are probably met by profound functional changes in the permeability and transfer functions of the cells that constitute the placental barrier.

Histomorphometry of the human placenta in pre-eclampsia associated with severe intrauterine growth retardation

The morphological changes in the functional structure of the placenta in cases of pre-eclampsia associated with severe intrauterine growth retardation have been investigated with quantitative analyses. It has been demonstrated that in pregnancies complicated by severe pre-eclampsia, the placenta can suffer significant morphological alterations characterized by an abnormal maturation or arborization of the terminal villi. The findings of this study suggest that, among the pathogenic mechanisms responsible for the observed placental changes, uteroplacental ischaemia is probably a dominant factor, and that any ill effects on fetal growth and viability are very likely to be related not only to the inadequate maternal supply of oxygen and nutrients but also to placental ischaemic damage.

Functional significance of the zonal morphologic differences in the normal human placenta: A morphometric study

Previous investigations have shown that the human placenta is a complex organ with different zones, each with a unique morphology. These zonal morphologic difference have been related to a probable blood PO2 gradient operating in the intervillous space. This study describes zonal variations in the vertical plane of the placenta by the application of different morphometric parameters. It demonstrates morphologic changes, which suggest that zonal differences may be the result of a physiologic adaptation of the placenta, which is dependent upon its structural relationships with the maternal tissues. This adaptation found in various areas of the placenta increases its functional efficiency.

Intrauterine growth retardation: Morphometry of the microvillous membrane of the human placenta

The syncytiotrophoblast microvillous membrane of the human placenta has been investigated with quantitative analyses in cases of severe fetal growth retardation associated with a marked reduction in the surface area of exchange at the peripheral villous level. This study has shown that, in placentae of intrauterine growth-retarded infants of unknown origin, there were morphological changes in the microvillous membrane characterized by an increase in the microvillous surface density and surface enlargement factor, associated with a reduction of the intermicrovillous space. It is not possible to state whether these morphological changes represent a delayed maturation of the placental tissue, or compensatory mechanisms to improve the functional efficiency of the placenta. In pre-eclampsia, these placental changes were much less pronounced, possibly due to severe uteroplacental ischaemia in this complication of pregnancy. Despite these morphological changes, both groups of placentae showed significant reductions in absolute values for the microvillous and total trophoblastic surface areas, which can have major implications on the functional efficiency of the placenta.

Morphological Changes in the Placentas of Smoking Mothers: A Histomorphometric Study

The morphological changes in the functional structure of placentas from women who smoke cigarettes during pregnancy have been investigated by quantitative, light-microscopic techniques. It has been demonstrated that the placentas of the smoking mothers were morphologically very similar to the placentas of the nonsmokers. The results only showed a tendency for the placentas in the study group to contain proportionally more nonparenchymal and less parenchymal tissue than the control group, mainly in terms of a relative reduction in the intervillous space volume and peripheral villous mass and surface area. The findings of this study support the hypothesis that the perinatal morbidity associated with cigarette smoking during pregnancy is probably more related to the ischemic and/or toxic effects of several compounds in tobacco smoke, partly on placental function and also directly on the fetus, than to significant alterations in the functional structure of the placenta.