Normative Values and Tables

Abstract

Quantitative structural and biochemical data concerning pregnancy, placental development, and composition of the term placenta are given in Tables 2 to 11. When examining the tables on placental morphometry and comparing the results from various authors, it is important to note that quantitative structural data are heavily influenced by the mode of sampling and by the preparation of the material. Because of the high degree of maternal and fetal vascularization, the placenta reacts immediately to changes in intravascular pressure. Thus, the mode of birth, the time elapsing from cessation of maternal and fetal blood flows to tissue fixation (Tables 7, 10), and the nature of cord clamping (Table 9) directly influence the volumetric relations of villi and intervillous space. In particular, parameters such as the width of fetal vessels, degree of fetal vascularization, maternofetal diffusion distance, and trophoblastic thickness are easily affected. Moreover, the composition of the fixative and its osmolarity (Table 11) as well as the mode of fixation (immersion versus perfusion fixation) are of importance. Normally, immersion fixation of the entire placenta or of small pieces is used. The more advanced methods, such as perfusion fixation (Burton et al., 1987) or puncture biopsy of the still maternally perfused placenta during cesarean section (Schweikhart & Kaufmann, 1977; Voigt et al., 1978; Sen et al., 1979), are time-consuming. When studying immersion-fixed material, however, one should keep in mind that this material differs quantitatively and qualitatively from the in vivo conditions (Tables 7, 10). It is impossible to include the results of numerous other valuable contributions to placental morphometry into these table. For further information on special issues, we refer to the following publications: placental growth development in relation to birth weight (Bouw et al., 1978); relation of placental weight to body size at 7 years of age and to abnormalities in children (Naeye, 1987); fetal and placental weights in relation to maternal weight (Auinger & Bauer, 1974); ultrasonographic measurements of volumetric growth of the placenta (Bleker et al., 1977); weight development of placenta and membranes during early pregnancy (Abramovich, 1969); ratio of gestational sac volume to crown-rump length during early pregnancy (Goldstein et al., 1986); villous surface area and villous volume densities in various placental regions and along different levels of the chorial basal axis (Teasdale, 1978; Boyd et al., 1980; Cabezon et al., 1985; Bacon et al., 1986); local variations of villous surface, fetal vascularization, and amount of vasculosyncytial membranes in the placentone (maternofetal circulatory unit) (Schuhmann et al., 1988); total villous surface in relation to fetal weight in normal and various pathological conditions (ClaveroNunez & Botella-Llusia, 1961, 1963); morphometric data affecting placental oxygen diffusion (Mayhew et al., 1984, 1986); computer measurement of the mass of syncytiotrophoblast (Boyd et al., 1983); ultrastructural morphometric analysis of the villous syncytiotrophoblast (Sala et al., 1983); microvillous surface enlargement of the villous surface (Teasdale & Jean-Jacques, 1985); comparison of villous structure after immersion and perfusion fixation (Burton et al., 1987).