The development of the human placental villous tree.

The present investigation was undertaken in order to achieve a better understanding of the dynamics of placental villous differentiation. Villous trees from human placentas from different stages of pregnancy (first trimester to full term) were isolated and studied by light microscopy and scanning electron microscopy. For light microscopy the trees were serially sectioned and two-dimensionally reconstructed. For scanning electron microscopy complete villous trees or freeze-cracked villi were studied. The most important finding was that the mesenchymal villi are continuously newly formed out of the trophoblastic sprouts throughout pregnancy. Because of this they exist in all stages of pregnancy and have to be considered the basis for growth and differentiation of the villous trees. In the first two trimesters they are the forerunners of the immature intermediate villi, whereas in the last trimester the mesenchymal villi are transformed into mature intermediate villi. The immature intermediate villi formed during the first two trimesters are developmental steps towards the stem villi. On the other hand, the mature intermediate villi, which only are developed during the last trimester, produce numerous terminal villi. The latter are not active outgrowths caused by proliferation of the trophoblast, but rather passive protrusions induced by capillary coiling due to excessive longitudinal growth of the fetal capillaries within the mature intermediate villi.

Effect of long-term hypoxia on oxygen transport properties of blood in pregnant guinea pigs.

Pregnant guinea pigs undergoing long-term hypoxia were studied and the results compared with those of control animals (pregnant, but non-hypoxic). Hypoxic animals demonstrated a decrease of O2 affinity (-7%) and an increase of O2 capacity (+35%). In addition, the HCT was found to be higher in the hypoxic group (+41%), causing haemorheological disadvantages; in a shear model study the blood of hypoxic animals had to be exposed to the gas compartment of the rheo-oxymeter up to 62% longer than that of the control group. We have postulated, that this rheological impairement is compensated, since no abnormalities in number and abortion rate of fetuses (due to a possible O2 delivery impairment) were found. Our morphological studies in fact support this opinion, showing e.g. more capillary branchings and loops and a reduction of diffusion distances between maternal and fetal blood in hypoxic guinea pig placentae. The results emphasize the importance of more detailed rheological studies in connection with other investigations for a complete description of compensatory mechanisms.

Alterations of the fetal capillary bed in the guinea pig placenta following long-term hypoxia.

Oxygen supply is an important regulator of the fetal placental capillarization. To determine the effects of long-term hypoxia on the fetal placental vessel arrangement pregnant guinea pigs were kept under hypoxic conditions (12% O2 for 45 days). Vessel casts showed a significant difference in branching and orientation of the vessels between the controls and the hypoxic animals. The hypoxic group had a less orientated capillary bed with increased branching and coiling. By light- and transmission electron microscopical studies, there was a decreased diffusion distance, a decreased diameter of the fetal capillaries, and an increased number of capillary cross-sections. These results are consistent with the hypothesis that chronic hypoxia is responsible for increased branching and coiling of the capillaries resulting in a dense network of short and narrow capillaries in the placenta.

[The importance of measuring both umbilical arteries for accuracy in Doppler ultrasound studies]. / Die Bedeutung der Messung beider Nabelarterien für die Aussagekraft dopplersonographischer Untersuchungen.

In a quarter of our Doppler investigations differences between the S/D-ratios of the arteries of one umbilical cord were more than 20%. In these cases one Doppler value was decided to be normal and the other to be pathological. In cases with two pathological values most caesarean sections because of fetal distress had to be performed and most SGA babies were born. There were relatively more caesarean sections and SGA babies in cases with one normal value and one pathological value than in cases with two normal Doppler values. Sensitivity and specificity of perinatal risks like intrauterine growth retardation or caesarean section because of fetal distress were different depending on which Doppler value was used to calculate these statistical parameters. Taking always the better values compared to the worse ones we found as greatest difference 20.0% for sensitivities and 24.1% for specificities. Taking the means of the better and the worse Doppler values we found as greatest difference 5.6% for sensitivities and 8.7% for specificities compared to the cases with two identical Doppler results. To decide whether the fetus is jeopardized and to describe the nutritional function of the placenta correctly by means of Doppler ultrasound of the umbilical artery we conclude that in some cases the investigation of both arteries is important to avoid false positive or false negative results.