Causes and consequences of fetal acidosis.

The fetus depends on the mother for placental exchange of oxygen and carbon dioxide. This in turn relies on adequate maternal blood gas concentrations, uterine blood supply, placental transfer and fetal gas transport. Disruption of any of these can cause fetal hypoxia, which, despite compensatory mechanisms, may lead to acidosis. When severe and acute (lasting hours), but especially if prolonged (days or weeks), hypoxia and therefore acidosis, are associated with significant morbidity and mortality with potential long term sequelae. Whether this damage is primarily due to reduced cell energy availability, as a result of hypoxia, or secondary to cell poisoning, as a result of acidosis, is unclear and indeed acidosis could simply be a marker of the cause and severity of the hypoxia. The very diVerent aetiologies of acute vs chronic acidosis and the possible consequences will be reviewed, whether directly caused by the acidosis or indirectly by the hypoxia