Funktionelle Morphologie der Placenta

Re-view and view on maturation disorders in the placenta

Until delivery, the placenta plays an important mediator role between mother and fetus. This unit is affected by peristatic conditions, such as acute or chronic maternal diseases, malnutrition, drugs, and others. But also genetic factors and fetal malformations due to embryonic developmental disorders may contribute to macroscopically visible changes and functional disorders of the placenta. In a constantly ongoing progress of maturation, the placenta records and saves changes due to fetal distress partly as maturation disorders. Understanding of maturation disorders might, therefore, be an important contribution to a better understanding of influences on villous differentiation and might improve follow up and fetal outcome to reduce recurrence risk. However, an internationally unified classification system of maturation disorders does not exist. In this review, terminology, trials, and classifications of villous maturation disorders are summed up and compared, to pinpoint the need of agreement on an international unified and reproducible classification of maturation disorders.

A new, clinically oriented, unifying and simple placental classification system

OBJECTIVE

At present there is no internationally accepted, clinically easy understandable, comprehensive morphological placental classification. This hampers international benchmarking and comparisons, and clinical research.

STUDY DESIGN

Internationally published criteria on morphological placental pathology were collected, standardized and focused into a comprehensive diagnosis category system. The idea was to create a clinically relevant placental pathology scheme related to major pathological processes. A system of nine main diagnostic categories (normal placenta included) was constructed. Pathologists and obstetricians discussed the mutual understanding of the wording in the reporting. The previously published diagnostic criteria were merged, structured and standardized. Through an interobserver correlation study on 315 placentas from intrauterine deaths and 31 controls (placentas from live births) the microscopic criteria in this classification system were tested on user-friendliness and reproducibility.

RESULTS

The clinical feedback has been very positive, focusing on the understandability and usefulness in patient follow-up. The interobserver agreement in the microscopic correlation study was in general good. The differences in agreement mainly reflected the degree of preciseness of the microscopic criteria, exemplified by excellent correlation in diagnosing acute chorioamnionitis. Maternal and fetal circulatory disorders need grading criteria and studies are needed to get more insight and clinical correlations of villitis and maturation disorders.

CONCLUSION

The clinically oriented, unifying and simple placental pathology classification system may work as a platform for standardization and international benchmarking. Further research is needed to define diagnostic criteria in staging and grading of some main diagnostic categories.

Fetal and maternal blood volumes in shed human placentae: discrepant results comparing morphometry to haemoglobin content

The maternal blood volume (MBV) and fetal blood volume (FBV) of shed human placentae delivered by caesarean section at term were measured using a morphometric technique and from the placental content of adult and fetal haemoglobin. MBV was 35.3 +/- 1.5 (s.e.m.) per cent by the former and 11.0 +/- 1.5 per cent by the latter technique. FBV was 11.0 +/- 0.7 and 9.0 +/- 0.6 per cent respectively (n = 6). Measurement of the dimensions of individual villi initially photomicrographed in 0.9 per cent NaCl and subsequently re-photographed in fixative suggested that individual villi shrank to 0.7 of their initial volume during fixation. It is suggested that morphometric measurement of MBV may lead to approximately a threefold overestimate because of relative MBV expansion and villous tissue shrinkage during the process of fixation without alteration in overall placental volume.

Morphology of placental villi after premature delivery and its clinical relevance

Based on a new concept of maturation of the placental villous tree and its disorders (synchronous and asynchronous immaturity, asynchronous maturity, hypermaturity, and terminal villi deficiency) we studied the possible effect of the placental villous tree on the premature onset of labour. In mature normal neonates irregular and asynchronous villous patterns were found in 50% of cases. In prematurely delivered neonates, only 33% of the corresponding placentas show synchronous immature villous patterns. Uterine bleeding in the first trimester was associated with a 42% of incidence of premature maturation of the villous tree. These findings strengthen the idea that hormonal imbalance in early pregnancy influenced villous development. In "prematurity without recognizable cause" there was a higher percentage of villous maldevelopment (33%) than that previously described in the literature. In severe pre-eclampsia combined with premature onset of labour, 60% of our cases showed hypermaturity of the villous trees. Synchronous immaturity was reduced to 15%. We conclude, that even a rather rough definition of the histological features of placental villi is sufficient to produce numerous correlations between clinical events preceding premature delivery and placental structure. So the influence of placenta on the premature onset of labour needs more attention.

A new type of congenital nephrotic syndrome

Description of a newborn male suffering from hydrops fetalis of unknown cause. Placenta showed multiple chorioangiomata. Coincidence of chorioangiomata of the placenta and hydrops fetalis has not been previously reported. The authors suggest a new kind of glomerulopathy as a cause of congenital nephrotic syndrome.

Screening for fetal and neonatal risk in the postdate pregnancy

One hundred four postdate pregnancies were managed according to a well-defined protocol calling for weekly oxytocin challenge tests and urinary estriols three times per week. Although the perinatal mortality rate in these patients was not increased there was a significant increase in the incidence of neonatal morbidity and complications. The clinical syndrome of dysmaturity was seen in 20 per cent of the neonates. When meconium was present in the amniotic fluid the incidence of neonatal and fetal complications was higher. The cesarean section rate was twice the normal rate, with nonprogression of labor being the commonest indication. It is recommended that: (1) pregnancies carried beyond 42 weeks do not require termination simply because they are post dates; (2) all postdate patients should be monitored during labor; (3) trained personnel to initiate neonatal resuscitation should be present at each postdate delivery.

[On the organization of the mature human placenta (author's transl)]

By means of macroscopic, histologic and enzyme histochemical methods the concept of Schuhmann and Wehler (1971) that the mature human placenta shows a morphological organization coincides with bloodflow-units was examined. The investigation deals with the existence and distribution of terminal villi which can be distinguished on the basis of histological and enzyme histochemical peculiarities. 90 placentas were available, 3 of which were premature. In 6 cases one half of the placenta or the whole organ was cut into serial sections. Mature placentas. Per dissected placenta on an average 6--7 regions with cavities in the intervillous space could be observed, which might correlate to the "placentones" postulated by Schuhmann and Wehler (1971). Using histological techniques at random scattered areas of different size of so-called "immature" villi exist in the near of the basal plate; a relation between these areas and the placentones cannot be seen. All enzymes investigated possess a lower activity in the syncytiotrophoblast of the immature villi than in the mature ones. The demonstration of phosphatases and lysosomal enzymes reveals groups of mature villi with increased activity; they form a patchy enzyme pattern. With the exception of dehydrogenases there is no relation between villi with special enzyme activities and the placentones. Premature placentas. The younger the placenta, the larger is the volume of immature villi. Result. At present a organization of the human placenta into morphological units which correlates to the bloodflow (placentones) cannot be seen. A principle of segmentation which bases on differences between the terminal villi cannot be demonstrated.

[A mathematical model for the description of oxygen-diffusion in the intervillous space of the human placenta (author's transl)]

The oxygen consumption has a central place in the complicated interaction between diminished oxygen supply and degenerative trophoblastic tissue change. In the present investigation, that serves as a mathematical model, the problem of the diffusion equation for the constant state is discussed and solved. It is shown that the diminishing of length of the radius of the maternal blood compartment has the same meaning as the decrease in the flow velocity. The influence of the mass transfer coefficient h on the oxygen partial pressure and on the oxygen transfer is investigated. The influence of parameter variations on the placental alterations during toxemia is discussed and their clinical importance is obvious. Our theoretical model elusidates the value of an early therapeutical approach in the case of toxemia.

[Problems of distinction of normal, arteficial and pathological structures in mature human placental villi. I. Ultrastructure of the syncytiotrophoblast (author's transl)]

Thirty-four mature human placentae were punctured in situ during cesarean section and fixed immediately. The ten cases which seemed normal according to clinical and morphological criteria were examined electron-microscopically. Findings won in ideal conditions after perfusion fixation of the guinea-pig placenta were compared to the human punction samples. The granular endoplasmic reticulum in the syncytium proved to be the most susceptable parameter. Its cisternae are narrow and arranged parallel to each other after optimal fixation. The larger the ischemic phase--already detectable after 2 min--, the more disorientated and dilated they become. The mitochondria only react considerably later. Similar structural alterations also occur in the course of pathological processes. The meaning of arteficially and pathologically induced ultrastructural changes and their interdependance are discussed.

[Quantitative investigations of the human placenta under normal conditions and in case of preeclampsia correlated to the human placenta-lactogen blood-level in the last third of pregnancy (author's transl)]

Thirty-two human placentas from normal and from pregnancies complicated by preeclampsia in last third of gestation were morphologically and morphometrically examined and correlated with human placenta-lactogen blood-level. HPL was determined by the radio-immunoassay (Carbon-Dextran-method). HPL-values, placenta villous surface, the weight of the newborn and placenta showed significant correlation. The placentas were classified according to the morphologic degree of severity (placenta-morphological-index) and compared to preeclamptic index (Goecke) and HPL-values. The results showed correlation between the studied datas according to the severity of preeclampsia. The significance of these results is discussed.

[Functional aspects of placental maturation in twin-pregnancies (author's transl)]

Multiple pregnancy placentas are especially efficient for examining the influence of placental maturity on fetal growth; extraplacental factors can be considered the same, and difference concerning the state of the child can be correlated with the conditions of the placental function. In 46 twin-couples placentas have been examined. In 21 cases placental parts varied in maturity. Children whose placentas had reached a better stage of maturity, were better in weight, length and Apgar score. Only in 3 cases with ripe placenta Apgar score was low (all cases were second-born children). In 25 twin-couples placentas of equal maturity were found, and the children showed insignificant differences. Differences concerning the Apgar score, could be caused by extraplacental etiological factors. 68 placental parts were correlated to the gestational age; a precocious placenta maturity was found in 31 cases, and a mature placenta in 26 cases. The importance of precocious placental maturity and its influence on the development and condition of the child post partum are being thoroughly discussed.

[Obliterative angiopathy of placental stem villi (author's transl)]

Out of 136 placentas with vascular obliterations, 25 cases were placentas of children born alive, in 92 cases the placentas belonged to children born dead. In 19 cases we had no data on the baby. In placentas of babies born alive, the same vascular changes (subtotal and total obliterations, septal partitions of vascular lumina) were found as in those of dead-born children, although considerably less severe. Vascular obliterations should not be considered as post-mortal alterations of the placenta blood vessels, since only quantitative differences could be proved. Septum-like partitions are hardly ever found in placentas of babies born alive, in dead-born babies they are more frequent. They seem to present recanalizations, and are understood as a compensation mechanism for a placental insufficiency caused by vascular obliterations. The accentuated collagenization of the placental periphery, noticed in placentas of babies born alive, is being interpreted as the consequence of an impaired blood circulation, caused by partial and total vascular obliterations. The high collagen rate in the placental periphery in placentas of the dead-born is probably a reaction to the diminished fetal circulation. Endangitis obliterations in 73 placentas out of 4600 pregnancies of cases with late abortions, premature deliveries, perinatal death, underweigh and small for gestational age babies, impaired adaptation in newborns of mothers with proteinuria and hypertension speak strongly for assuming that endangitis obliterans presents a form of placental insufficiency. Endangitis obliterans of the placental blood-vessels has, however, been discovered frequently after Rubella infection in early pregnancy. The etiological factors of the endovascular process can be multiple, the morphological and the pathophysiological reactions are the same.

[Hydroxyproline concentration in normal and pathologic altered placentae of the second part of pregnancy (author's transl)]

By using microanalytic Hydroxyproline (HP)-determination method (Woessner and Stegemann) the content of collagen in 50 normal and pathologicaltered placentae of the second part of pregnancy was measured. A positive linear correlation is demonstrated between HP-concentration and age of pregnancy in normal placentae. Most of the pathologic altered placentae have a lower content of collagen. HP-content measured in main stem and terminal villi of further 35 placentae showed the essential influence of the main stem villi on total placental collagen concentration. In the second part of gestation the HP-concentrations of the main stem villi rise on a factor about 5-6, in the terminal villi they remain constant. The values measured within both groups of villi show a great dispersion. The quantitative results were compared with the histology of the placentae.

Placental insufficiency in relation to postterm pregnancy and fetal postmaturity. Evaluation of fetoplacental function; management of the postterm gravida

As pregnancy extends post term, incidence of placental insufficiency, fetal postmaturity (dysmaturity), and fetal perinatal death increases rapidly as a consequence of reduced respiratory and nutritive placental function. Despite a compensatory fetoplacental respiratory reserve capacity, fetal distress is observed in about one third of postterm pregnancies. On a biochemical level, placental pathophysiology in postterm-postmaturity pregnancies is not well understood. Postmaturity is correlated with increased incidence of placental lesions, fetal hypoxia-asphyxia, intrauterine growth retardation, increased perinatal death, and neonatal morbidity. Early diagnosis of fetal postmaturity is difficult because currently applied test methods allow recognition only when placental insufficiency is far progressed. Therefore, in postterm gravidas with a favorable cervix, induction of labor should be considered; in older primigravidas, in whom fetal losses may be sevenfold increased, or in multiparas with a history of obstetric complications, pregnancy may require termination by cesarean section. Pregnancy may be allowed to continue under close supervision in cases of uncertainty of duration of gestation, in gravidas carrying small babies, in young primigravidas, and in multigravidas in whom placentofetal function tests are normal. As long as fetal scalp blood sampling during labor does not show fetal acidosis, despite abnormal fetal heart rate pattern and meconium release, vaginal delivery may be attempted when deemed possible within a few hours. In parturients attention must be paid to the extent of uterine activity and type of medication; lateral positioning of the gravida and maternal oxygen breathing, facilitating fetal oxygen supply, are important features. Because during bearing-down efforts placentofetal respiratory reserves of postterm gravidas may become further compromised, immediate delivery by forceps or vacuum extraction may be considered. After delivery the umbilical cord should not be clamped immediately in order to allow increased fetal blood supply and to counteract fetal hypovolemia. Dysmature newborn infants require special care by the neonatologist.

[Light and electron microscopic investigations on the chorionic plate of the human placenta at term (author's transl)]

The chorionic plate of the human placenta at term consists of amniotic epithelium, amniotic connective tissue, intermediate layer, chorionic connective tissue, cytotrophoblast, and syncytiotrophoblast. - The connective tissue layers are divided into unorientated (situated just below the amniotic epithelium and in direct contact with the trophoblast) and orientated layers (between the two unorientated connective tissue layers). Besides an accelular border below the amniotic epithelium the connective tissue includes fibrocytes, fibroblasts, histiocytes, and old Hofbauer cells in the intermediate layer. - From the edge of the chorionic plate to its centre, the number of well preserved cytotrophoblasts decreases; instead of them especially intercellular substances (subchorial fibrinoid) but also degenerating cells predominate. In the trophoblast layer rests of chorionic villi are localized. Among the intact cytotrophoblasts 4 types can be distinguished (less differentiated, well differentiated, spongiotrophoblast-like, and glycogen-rich cytotrophoblastic cells). They are interpreted as different developmental stages of one and the same cell population. - The syncytiotrophoblast is inter rupted at many places; only fragments can be observed. Then cytotrophoblastic cells or intercellular substances may form the border to the intervillous space.