Conflicting data on intervillous circulation in early pregnancy

Onset of maternal arterial blood flow and placental oxidative stress. A possible factor in human early pregnancy failure

The aim was to measure changes in the oxygen tension within the human placenta associated with onset of the maternal arterial circulation at the end of the first trimester of pregnancy, and the impact on placental tissues. Using a multiparameter probe we established that the oxygen tension rises steeply from <20 mmHg at 8 weeks of gestation to >50 mmHg at 12 weeks. This rise coincides with morphological changes in the uterine arteries that allow free flow of maternal blood into the placenta, and is associated with increases in the mRNA concentrations and activities of the antioxidant enzymes catalase, glutathione peroxidase, and manganese and copper/zinc superoxide dismutase within placental tissues. Between 8 to 9 weeks there is a sharp peak of expression of the inducible form of heat shock protein 70, formation of nitrotyrosine residues, and derangement of the mitochondrial cristae within the syncytiotrophoblast. We conclude that a burst of oxidative stress occurs in the normal placenta as the maternal circulation is established. We speculate that this may serve a physiological role in stimulating normal placental differentiation, but may also be a factor in the pathogenesis of pre-eclampsia and early pregnancy failure if antioxidant defenses are depleted.

Intervillous circulation in all three trimesters of normal pregnancy assessed by color Doppler

Our cross-sectional study included 115 healthy pregnant women in gestational age between 7 and 24 weeks. The aim of the study was to compare resistance (RI) and pulsatility (PI) indices, peak systolic velocity (PSV), end-diastolic velocity, and temporal averaged maximum velocity (TAMV) of the spiral arteries and vessels within the intervillous space in all three trimesters of pregnancy. The impedance to blood flow within the intervillous space significantly decreased towards the mid-pregnancy (p < 0.01) and then remained stable. Blood flow velocities within the intervillous space expressed by PSV, EDV and TAMV increased significantly (p < 0.01) towards the mid-pregnancy. After reaching the plateau between 16 and 22 weeks of gestation, these parameters remained almost constant until the 36th gestational week. Near the term low-significant decrease of blood flow velocities was noted: for PSV and TAMV p < 0.07, and for EDV p < 0.05. A significant increase in continuous intervillous blood flow velocity was noted from the 11th week onward (28 +/- 12 vs. 36 +/- 12) until the 36th week of gestation (36 +/- 12 cm/s). The first report of the haemodynamic changes within the intervillous space during pregnancy may have implication in better understanding of the metabolical interchange between maternal and fetal side.