Oxytocin in pregnancy
- Oxytocin is a polypeptide hormone synthesised by the supraoptic and paraventricular nuclei of hypothalamus
- It is secreted by the posterior pituitary into the blood stream
Actions of oxytocin
- Main action is on uterine myometrium
- It promotes uterine muscle contraction
- The action is greater on pregnant uterus as it has increased number of oxytocin receptors
- Contraction of myoepithelial cells in breast cause expression of breast milk
- Smooth muscle relaxation and vasodilation
- ADH (Anti Diuretic Hormone) like effect in large doses, causes water intoxication
Mechanism of action on uterine myometrium:
- It acts by releasing cAMP
- This in turn results in the release of Ca2+ from the sarcoplasmic reticulum
- Calcium causes contraction of muscle
Uses of oxytocin
- Induction and accentuation of labour
- Active management of third stage of labour – given after separation of placenta for promoting uterine contraction and stoppage of bleeding
- Atonic PPH – to control bleeding and promote uterine contraction
- Second trimester abortion (medical termination of pregnancy) as an adjunct to prostaglandins
- Abortion and hydatidiform mole – to decrease bleeding during suction evacuation and to promote uterine contraction
- Oxytocin challenge test (Contraction stress test) – to test whether fetus can cope with the stress of labour
- Oxytocin sensitivity test
Side effects of oxytocin
- Hyperstimulation of uterus
- Hypotension – due to vasodilation
- Hypertension – especially when given with methergine
- Water intoxication – when high dose is given with large quantities of fluids – can cause convulsions and coma
- Neonatal jaundice
- Ventricular premature beats – in case of IV bolus of oxytocin
- Myocardial ischemia and ventricular fibrillation – especially in those with heart disease
