The hypoxic fetus as a patient: adaptations to the intrauterine environment

Fetal oxygen delivery and uptake are essential for intrauterine growth and survival. The placenta is the centre of physiological exchange of oxygen, nutrients and metabolic waste between mother and fetus. Many hypoxic fetal growth-restricted (FGR) fetuses are the result of what is simplified as intrauterine 'asphyxia'. Understanding the factors that determine placental function, especially its ability to facilitate respiratory gas exchange, is essential. These elements are key to unravelling the pathophysiological processes involved in pregnancy complications. The possibility of measuring umbilical uptake in human pregnancies has been developed in recent years by the potential to calculate umbilical blood flow through ultrasound measurements and then use the values of oxygenation from the umbilical artery and vein obtained at cesarean section. In normal fetuses, oxygen delivery on a per kg basis is remarkably similar to that of other animal species. The human FGR fetus shows a strikingly reduced umbilical delivery and uptake of oxygen. Umbilical glucose uptake is also significantly reduced but glucose/oxygen quotient is significantly increased in FGR pregnancy. The human fetus in FGR pregnancy triggers adaptive mechanisms to reduce its metabolic rate, matching the proportion of substrate consumption relative to oxygen delivery as a survival strategy during complicated pregnancy. This article is part of the discussion meeting issue 'Pregnancy at high altitude: the challenge of hypoxia'.