Quantitative Studies of Human Placenta I.

Abstract

Eighteen term placentas from a middle-class North American urban population were examined by stereologic techniques and an image quantizer. The trimmed placental weight averaged 469 g, of which 339 g was Ê»functional parenchyma’ and 130 g Ê»nonparenchymal tissue’ (decidual and chorionic plates and large vessels and pathological components such as infarcts). Microscopically, the parenchyma was divided into villi and intervillous space. The volume of intervillous space was, at 110 cm³, significantly larger than that of the villous capillaries, which measured 30 cm³. The mass of the chorionic villi averaged 214 g and comprised 168 g of peripheral and 46 g of stem villi. Most of the 60 g of trophoblast and of the 31.5 g of fibroblasts, and a significant fraction of the 91 g of collagenous stroma were present in the peripheral villi. The longest diameter of the peripheral villi averaged 74 µm and their cross-sectional area 1,100 µm². The surface area of the peripheral villi was 16 m² and that of the corresponding xillous capillaries 12 m². A model for estimating placental oxygen diffusion capacity (Dpo₂) was constructed on the basis of these stereologic measurements. The resistance to oxygen diffusion from maternal to fetal red cells in the placenta was attributed to five serial compartments i.e. (1) the oxygen-hemoglobin interactions in the maternal red cells in the intervillous space; (2) the maternal blood plasma in the intervillous space; (3) the villous membrane comprising syncytiotrophoblast, basement membrane, connective tissue and fetal capillary wall; (4) the fetal blood plasma, in the villous capillaries and (5) the oxygen-hemoglobin interactions in the fetal red cells present in the villous capillaries. The diffusion capacity of the placental membrane (D_M), comprising (2–4), was 3.256 and that of the total placenta 3.086 ml oxygen min^––¹ · mm Hg^––1. The corresponding specific diffusion capacities per 100 g of placenta were 0.694 for the placental membrane (D_M/w) and 0.658 ml. min^––1 · mm Hg^––1 for the whole placenta (D_P/_w). The resistance of the villous membrane was consequently the limiting factor in oxygen diffusion, both when considering the 110-ml maternal and 30-ml fetal blood volumes as the effective exchangers or when considering a single capillary transit for oxygen with 10 ml in each of the maternal and fetal compartments.

Gross Placental Structure in a Low-Risk Population of Singleton, Term, First-Born Infants

“…However, these studies generally had higher mean gestational ages and considered mothers with parity greater than zero. The mean placental weight in this study is higher than that reported in a sample of 10 325 American women who delivered at term (447 g [61]; see also 451 g [41], 452 g [26], 469 g [62], and 473 g [63]). In this study, the mean (time-adjusted) placental-fetal weight ratio of 13.7 (62.0) is also lower than the British samples (boys 15.4 6 2.8 and girls 15.7 6 2.9 [40], boys 15.9 6 3.5 and girls 16.0 6 3.1 [60]).…”

Oxygen diffusive conductance in placentae from control and diabetic women

“…In the present study, these two compartments accounted for 78-83 % of total resistance. In studies on term placentae at low and high altitude, values have varied between 70 % and 90 % [17,29,40]. Despite this agreement over relative resistances, Dp values differ in the present as compared to earlier investigations.…”

A trans-homologue interaction between reciprocally imprinted miR-127 and Rtl1 regulates placenta development

“…The alterations in MBS and FC surface area would affect nutrient and oxygen supply to the fetus and contribute to the observed fetal growth restriction. The theoretical diffusion capacity (TDC) and specific diffusion capacity (SDC) are barometers for the potential ability of small molecules such as oxygen to transfer by passive diffusion from mother to fetus (Laga et al, 1973). The TDC and SDC values of the mutant placentae indicate that ΔmiR-127 mice have a higher diffusive capacity than WT and, conversely, that ΔRtl1 placentae have a reduced capacity (supplementary material Table S3).…”