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

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