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 place nta associated with onset of the maternal arterial circulation at the end o f the first trimester of pregnancy, and the impact on placental tissues. Us ing a multiparameter probe we established that the oxygen tension rises ste eply from <20 mmHg at 8 weeks of gestation to >50 mmHg at 12 weeks, This ri se coincides with morphological changes in the uterine arteries that allow free flow of maternal blood into the placenta, and is associated with incre ases in the mRNA concentrations and activities of the antioxidant enzymes c atalase, glutathione peroxidase, and manganese and copper/zinc superoxide d ismutase within placental tissues. Between 8 to 9 weeks there is a sharp pe ak of expression of the inducible form of heat shock protein 70, formation of nitrotyrosine residues, and derangement of the mitochondrial cristae wit hin the syncytiotrophoblast. We conclude that a burst of oxidative stress o ccurs in the normal placenta as the maternal circulation is established. We speculate that this may serve a physiological role in stimulating normal p lacental differentiation, but may also be a factor in the pathogenesis of p re-eclampsia and early pregnancy failure if antioxidant defenses are deplet ed.