Expansion
Progesterone relaxes smooth muscle, slowing emptying and reducing sphincter tone
Expansion
Progesterone relaxes smooth muscle throughout the gut:
- Lower oesophageal sphincter tone falls, and the enlarging uterus raises intra-abdominal pressure and displaces the stomach, so reflux affects most women
- Gastric emptying is essentially normal in pregnancy but delayed in labour and by opioids
- Intestinal transit slows, causing constipation, aided by increased water absorption
- Gallbladder emptying is impaired and bile becomes more lithogenic, so gallstones are commoner
Nausea and vomiting affect up to 80 per cent, peaking at 8 to 12 weeks, attributed to human chorionic gonadotrophin and oestrogen. Hyperemesis gravidarum is the severe form, with weight loss, dehydration, ketosis and electrolyte disturbance, and carries a risk of Wernicke encephalopathy if thiamine is not given.
The anaesthetic implication is important: from about 16 to 20 weeks all pregnant women are treated as having a full stomach, warranting rapid sequence induction and acid prophylaxis.