Prostaglandins in Obstetrics and Gynaecology
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Direct answer
Prostaglandins are lipid mediators used in obstetrics to ripen the cervix, induce labour and control postpartum haemorrhage. Dinoprostone (PGE2) is used for cervical ripening, misoprostol (a PGE1 analogue) is given orally or vaginally for induction, and carboprost (PGF2 alpha) is the injectable agent for uterine atony. Active asthma and cardiac disease exclude carboprost, and every agent carries a risk of uterine hyperstimulation that calls for monitoring.
What you must remember
- Dinoprostone: available as a vaginal insert or gel, used to ripen the cervix before induction, and stopped when regular contractions establish or hyperstimulation occurs.
- Misoprostol: a PGE1 analogue given orally or vaginally for labour induction, and used with mifepristone for medical termination of pregnancy, with dosing that varies by protocol.
- Carboprost: a PGF2 alpha analogue given intramuscularly for uterine atony that has not responded to oxytocin, and also used in second-trimester termination.
- Contraindications: active asthma and cardiac disease for carboprost, placenta praevia or vasa praevia for induction, and previous uterine surgery such as caesarean section, which is a relative concern.
- Hyperstimulation: tachysystole with reduced fetal oxygenation is the main hazard of intrapartum prostaglandins, so the contraction pattern and the trace are watched closely.
- Uterine rupture: the risk is higher in a scarred uterus, so prostaglandin induction is used cautiously or avoided after caesarean section.
Comparing the three agents
The three agents differ in their receptor action, route and use, and examiners test the pairing of agent, use and key contraindication more than the chemistry. The table lists the usual pairings in a form that is easy to recall in the examination hall.
| Agent | Usual route | Main use | Key caution |
|---|---|---|---|
| Dinoprostone (PGE2) | Vaginal insert or gel | Cervical ripening and induction | Hyperstimulation, asthma |
| Misoprostol (PGE1) | Oral or vaginal | Induction, postpartum haemorrhage, medical abortion | Hyperstimulation, dose protocol |
| Carboprost (PGF2 alpha) | Intramuscular | Atonic postpartum haemorrhage, termination | Asthma, cardiac disease, bronchospasm |
The memorable pattern is that the PGE agents ripen the cervix and induce labour, while the PGF2 alpha agent contracts the uterus to control haemorrhage. Doses vary between protocols and products, so the examination answer usually names the agent, the route and the key contraindication rather than a fixed number.
Monitoring the trace is the common thread across all three, because each agent can cause hyperstimulation. Viva questions often ask which agent is safest in a given history, and the answer depends on the contraindication, not the potency.
Where the exam tries to catch you
Most questions test contraindications and the choice of agent for a given clinical situation.
- Trap: using carboprost in a woman with asthma because it is a uterotonic for postpartum haemorrhage Correct: carboprost is contraindicated with active asthma, so alternatives such as oxytocin or misoprostol are considered.
- Trap: giving dinoprostone routinely to a woman with a previous caesarean section Correct: previous uterine surgery raises the rupture risk, so prostaglandin induction is avoided or used with great caution.
- Trap: assuming misoprostol is safe without monitoring because the dose is small Correct: hyperstimulation can occur even at low doses, so the contraction frequency and the fetal trace must be watched.
Frequently asked questions
Which prostaglandin is given intramuscularly for postpartum haemorrhage?
Carboprost, a PGF2 alpha analogue, is the prostaglandin given intramuscularly for postpartum haemorrhage from uterine atony. It is used when oxytocin has failed to control the bleeding. Carboprost must be avoided in women with active asthma because it can cause bronchospasm.
Why is carboprost contraindicated in asthma?
Carboprost causes bronchoconstriction, so it can precipitate severe bronchospasm in women with asthma. This is a classic exam contraindication for carboprost in obstetrics. Alternative uterotonics are chosen in such women.
What is the main hazard of misoprostol used for labour induction?
Uterine hyperstimulation with tachysystole and fetal heart rate changes is the main hazard of misoprostol used for labour induction. Its effect is unpredictable, so the contraction pattern and fetal trace must be watched. Dose and interval follow the local protocol being used.
Which prostaglandin is used for cervical ripening before induction?
Dinoprostone is the prostaglandin most often used for cervical ripening before induction of labour. It is given as a vaginal insert or gel. Misoprostol is also widely used for ripening, depending on the local protocol.
Why is previous caesarean section a concern with prostaglandin induction?
Prostaglandin induction after caesarean section raises concern because strong uterine contractions increase the risk of scar rupture. Uterine rupture is the key catastrophic complication to avoid. Such women are usually managed with great caution, or an elective repeat caesarean section is offered.