Cervical Pessary for Preterm Birth Prevention
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Direct answer
A cervical pessary is a silicone device fitted in the vagina around the cervix to support it and reduce cervical shortening, used to lower preterm birth risk in selected women. Its role is still being evaluated, and trial results have been mixed, so it is used selectively under specialist care. A short cervix on mid-trimester ultrasound is the usual trigger for discussing a pessary.
What you must remember
- Mechanism: A silicone ring or cup placed over the cervix to support it and reduce funnelling.
- Trigger: A short cervix on mid-trimester transvaginal ultrasound, with a length below 25 mm as a commonly used threshold.
- Progesterone in twins: Has not been shown to prevent preterm birth in twins with a short cervix.
- Cerclage: Indicated for cervical insufficiency from history, such as previous mid-trimester loss, not for a short cervix alone.
- Cerclage types: The McDonald and Shirodkar techniques are the commonly described approaches.
- Complications: Discharge, bleeding, infection and pessary dislodgement, each needing prompt review.
- Infection risk: Any fever or foul discharge needs urgent assessment, since infection can progress to chorioamnionitis.
- Removal: Usually near term, or earlier if labour begins, bleeding occurs or the pessary leaks.
A stepwise approach to insertion
A woman with a twin pregnancy and a cervical length of 18 mm at 22 weeks is a typical case for discussing a pessary. The steps below set out a careful approach to insertion and follow-up.
- Confirm the indication: Check cervical length by transvaginal ultrasound, and document gestation, the type of pregnancy and any previous preterm birth.
- Prepare the woman: Obtain informed consent, ask her to empty the bladder, and inspect the cervix with a speculum to exclude infection or dilatation.
- Choose the size: Select a pessary that fits the vaginal length, so it sits around the cervix without pressing on the urethra.
- Insert and position: Place the pessary so the cervix sits within its central cup, then confirm the position with a speculum examination.
- Check and follow up: Review for discharge, bleeding and pain, with scheduled ultrasound and cervical checks.
- Remove at term or earlier if needed: Remove the pessary near term, or sooner if labour, bleeding or leakage occurs.
A misplaced pessary fails to support the cervix, so the post-insertion speculum check is not optional. Each follow-up visit also gives an opportunity to detect infection early.
Where the exam tries to catch you
Most questions here test whether the student matches the intervention to the clinical situation rather than to a single marker.
- Trap: Choosing cerclage for any short cervix Correct: Cerclage is indicated for cervical insufficiency from history, not for a short cervix found on scan alone.
- Trap: Giving progesterone to a twin pregnancy with a short cervix because it works in singletons Correct: Progesterone has not shown benefit in twins with a short cervix, so it is not the standard choice there.
- Trap: Treating a pessary as risk-free without follow-up Correct: Pessaries carry risks of discharge, bleeding and infection, so the woman needs regular review.
Frequently asked questions
Which pregnancies are considered for a cervical pessary?
A cervical pessary is considered in selected pregnancies with a short cervix on mid-trimester transvaginal ultrasound, including some twin pregnancies. It is usually offered in specialist centres. Evidence is still evolving and mixed, so use is individualised.
Is progesterone effective for preventing preterm birth in twins?
Progesterone has not been shown to prevent preterm birth in twin pregnancies with a short cervix. Its benefit in singleton pregnancies with a short cervix does not carry over to twins. Guidelines therefore do not recommend routine progesterone for twins with a short cervix.
When is a cerclage indicated?
A cerclage is indicated for cervical insufficiency, usually defined by a history of mid-trimester loss or preterm birth attributed to a short or dilated cervix. The McDonald and Shirodkar techniques are the commonly described approaches. Cerclage is not supported for a short cervix found on scan alone without such history.
When should a cervical pessary be removed?
A cervical pessary is usually removed near term, commonly around 36 to 37 weeks, or earlier if labour starts, bleeding occurs or the pessary leaks. Removal is done under speculum view and is generally a simple procedure. Labour is then managed as usual.
What are the main complications of a cervical pessary?
The main complications of a cervical pessary are vaginal discharge, bleeding, infection and dislodgement, and each needs prompt review. Infection is the most serious, since it can progress to chorioamnionitis or preterm labour. Any fever or foul discharge should prompt urgent assessment.