The combination of an increased tendency to gastro-oesophageal reflux, reduced gastric pH and increased gastric volumes predisposes pregnant women to aspiration of gastric contents. This effect, combined with the shorter time available for airway manipulation (due to the rapid fall in PaO₂ during apnoea) and the increased incidence of difficult intubation leads to increased risk of aspiration, hypoxaemia and death during obstetric general anaesthesia.

Mendelson first described the acid aspiration syndrome in obstetric patients.

When general anaesthesia is required in obstetrics strategies are combined to reduce the risk of acid aspiration, including:

• Reduction of gastric acidity
• Rapid sequence induction with cricoid pressure