There are numerous medications used during labour. This section includes the main ones in a single place to clarify what they are and how they work.
Oxytocin is a hormone secreted by the posterior pituitary gland. It is produced in the hypothalamus, but travels to the pituitary before being released into the general circulation. It has several effects on mood and social interactions in everyday life, but also plays a vital role in labour and delivery.
Oxytocin stimulates the ripening of the cervix and contractions of the uterus during labour and delivery. It also plays a role in lactation during breastfeeding.
Infusions of oxytocin are used to:
- Induce labour
- Progress labour
- Improve the frequency and strength of uterine contractions
- Prevent or treat postpartum haemorrhage
Syntocinon is a brand name for oxytocin produced by one drug company.
Atosiban is an oxytocin receptor antagonist that can be used as an alternative to nifedipine for tocolysis in premature labour (when nifedipine is contraindicated).
Ergometrine is derived from ergot plants. It stimulates smooth muscle contraction, both in the uterus and blood vessels. This makes it useful for delivery of the placenta and to reduce postpartum bleeding. It may be used during the third stage of labour (delivery of the placenta) and postpartum to prevent and treat postpartum haemorrhage. It is only used after delivery of the baby, not in the first or second stage.
Due to the action on the smooth muscle in blood vessels and gastrointestinal tract, it can cause several side effects, including hypertension, diarrhoea, vomiting and angina. It needs to be avoided in eclampsia, and used only with significant caution in patients with hypertension.
Syntometrine is a combination drug containing oxytocin (Syntocinon) and ergometrine. It can be used for prevention or treatment of postpartum haemorrhage.
Prostaglandins act like local hormones, triggering specific effects in local tissues. Tissues throughout the entire body contain and respond to prostaglandins. They play a crucial role in menstruation and labour by stimulating contraction of the uterine muscles. They also have a role in ripening the cervix before delivery.
One key prostaglandin to be aware of is dinoprostone, which is prostaglandin E2. This is used for induction of labour, and can come in one of three forms:
- Vaginal pessaries (Propess)
- Vaginal tablets (Prostin tablets)
- Vaginal gel (Prostin gel)
TOM TIP: Prostaglandins act as vasodilators, and lower blood pressure. NSAIDs such as ibuprofen and naproxen inhibit the action of prostaglandins. As a result, NSAIDs can increase blood pressure. NSAIDs are generally avoided in pregnancy, and also after delivery in women with raised blood pressure (although research has shed doubt on whether the effects on blood pressure is significant enough to justify avoiding them). NSAIDs (e.g. ibuprofen and mefenamic acid) are useful in treating dysmenorrhoea (painful periods), as they reduce the painful cramping of the uterus during menstruation.
Misoprostol is a prostaglandin analogue, meaning it binds to prostaglandin receptors and activates them. It is used as medical management in miscarriage, to help complete the miscarriage. Misoprostol is used alongside mifepristone for abortions, and induction of labour after intrauterine fetal death.
Mifepristone is an anti-progestogen medication that blocks the action of progesterone, halting the pregnancy and ripening the cervix. It enhances the effects of prostaglandins to stimulate contraction of the uterus. Mifepristone is used alongside misoprostol for abortions, and induction of labour after intrauterine fetal death. It is not used during pregnancy with a healthy living fetus.
Nifedipine is a calcium channel blocker that acts to reduce smooth muscle contraction in blood vessels and the uterus. It has two main uses in pregnancy:
- Reduce blood pressure in hypertension and pre-eclampsia
- Tocolysis in premature labour, where it suppresses uterine activity and delays the onset of labour
Terbutaline is a beta-2 agonist, similar to salbutamol. It stimulates beta-2 adrenergic receptors. It acts on the smooth muscle of the uterus to suppress uterine contractions. It is used for tocolysis in uterine hyperstimulation, notably when the uterine contractions become excessive during induction of labour.
Carboprost is a synthetic prostaglandin analogue, meaning it binds to prostaglandin receptors. It stimulates uterine contraction. It is given as a deep intramuscular injection in postpartum haemorrhage, where ergometrine and oxytocin have been inadequate. Notably, it needs to be avoided or used with particular caution in patients with asthma, as it can cause a potentially life-threatening exacerbation of the asthma.
Tranexamic acid is an antifibrinolytic medication that reduces bleeding. It binds to plasminogen and prevents it from converting to plasmin. Plasmin is an enzyme that works to dissolve the fibrin within blood clots. Fibrin is a protein that helps hold blood clots together. Therefore, by decreasing the activity of the enzyme plasmin, tranexamic acid helps prevent the breakdown of blood clots.
Tranexamic acid is used in the prevention and treatment of postpartum haemorrhage.
Last updated September 2020