Gef��verschl�sse in der Placenta von Totgeborenen

Physiological and pathological morphology of the umbilical and placental circulation

Closure mechanisms of fetal vessels are essential after birth. They are physiological. The speedy and characteristic constriction is made possible by the special construction of the fetal vessels. The so-called "folds of Hoboken" in the umbilical artery initially form tapered constrictions which quickly extend to longer sections of the vessel. The contractions continue to include the chorion plate and the villi. Due to a lack of lamina elastica interna, a protrusion of pear shaped, expanded mediamyocytes and myofibroblasts is possible which reduces the cross-sectional area of these vessels. Similar, but lasting reductions in the cross-section of the villous arteries due to a fibrous-muscular media occur in the second half of pregnancy (IVth sign of maturity). Closure of the fetal vessels during intrauterine life leads to placental insufficiency of fetal death in utero. The endarteritis obliterans closes villous vessels by means of a connective tissue plug which starts on one side of the vessel and continues across the whole width of the lumen. The periphery dependent of these villi remains avascular, as the placenta is limited in its resorptive capabilities. In the case of intrauterine asphyxia, intravasal fibrinthrombi form as a sign of subacute insufficiency in the utero-placental circulation. A decompression collapse occurs in the fetal circulation, when fetal death occurs with continuing maternal circulation.

[The so-called recanalisation of cotyledonary vessels with endangitis obliterans of placenta vessels (author's transl)]

With a graphic reconstruction on serial sections, performed with placentas which altogether showed so-called recanalisation, it is possible to work out the fact, that the recanalisation is an effect of the paravascular capillary network and with it to clarify the problem of the so-called recanalisation. It is proved, that the paravascular capillaries undertake compensatory hemodynamic functions and this undertaking of function prevents a complete occlusion of the cotyledonary vessels, so that you have to speak of restlumen and restflow but not of recanalisation. The endangitis obliterans of cotyledonary vessels is again unequivocally pointed out by this phenomenon as a intravital process.

[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.