Cervical cerclage — structured SAQ (15 marks)

(a) Indication classes and which applies here (3 marks)

One mark for the framework of three indications; one for naming the applicable class; one for the reasoning. ^[1]

• Three indication classes: history-indicated (prophylactic, placed early in the second trimester on obstetric history), ultrasound-indicated (placed when serial transvaginal cervical length screening shows a short cervix in a woman at risk), and examination-indicated or rescue (placed when the cervix is already dilating painlessly after excluding labour and infection).^[1]
• This woman fits the ultrasound-indicated class: a singleton with a prior spontaneous preterm birth and a cervix under 25 mm before 24 weeks (here 18 mm at 21 weeks).^[1]
• She is asymptomatic, so this is not a rescue scenario; the indication is ultrasound-driven in an at-risk woman.^[1]

(b) Evidence supporting cerclage in this woman (4 marks)

One mark for citing the right meta-analysis; up to three marks for the key results. ^[2][3]

• The supporting evidence is the Berghella individual-patient-data meta-analysis of women with a singleton gestation, a previous spontaneous preterm birth, and a cervical length under 25 mm before 24 weeks.^[2]
• Cerclage reduced preterm birth before 35 weeks from 41.3 per cent to 28.4 per cent (relative risk 0.70, 95 per cent CI 0.55–0.89), with significant reductions at every earlier gestational threshold.^[2]
• Composite perinatal mortality and morbidity were significantly reduced (15.6 per cent vs 24.8 per cent; relative risk 0.64, 95 per cent CI 0.45–0.91).^[2]
• Contrast with the To et al. trial, which found no benefit of cerclage for a short cervix in unselected women (22 per cent vs 26 per cent before 33 weeks; RR 0.84, not significant) — the responder phenotype is what makes the difference.^[3]

(c) Counselling and operative technique (4 marks)

One mark per point, maximum four. ^[1]

• Counsel on the expected benefit in her phenotype, the alternative of expectant management with surveillance, and the risks — infection, rupture of membranes, bleeding, cervical trauma, preterm labour, and the need for stitch removal.
• Confirm gestational age, viability and a satisfactory anomaly screen before a prophylactic or ultrasound-indicated stitch; exclude ruptured membranes, chorioamnionitis, heavy bleeding and active labour.^[1]
• Technique — McDonald: a purse-string suture around the vaginal cervix at the cervicovaginal junction, tied to reduce the internal os, with the knot left accessible for removal at 36 to 37 weeks.^[1]
• Alternative technique — Shirodkar: dissection of the bladder (and rectal) reflections to place a submucosal band higher on the cervix, nearer the internal os, used when a higher, more durable stitch is wanted.^[1]

(d) Recommendation after a failed vaginal cerclage (4 marks)

One mark for the recommendation; up to three for the evidence and reasoning. ^[4]

• A pregnancy lost despite a vaginal cerclage is a failed vaginal cerclage, and the woman should be offered a transabdominal cerclage in the next pregnancy.^[4]
• The MAVRIC trial compared transabdominal, high vaginal and low vaginal cerclage in women with a history of failed cerclage; transabdominal cerclage was superior to low vaginal cerclage for delivery before 32 weeks (8 per cent vs 33 per cent; relative risk 0.23, 95 per cent CI 0.07–0.76), a number needed to treat of 3.9.^[4]
• Transabdominal cerclage is placed before conception or at 11 to 14 weeks and mandates caesarean delivery.^[1][4]
• Counsel that the suture sits at the internal os, above the anatomical cervix, which is why it succeeds where a vaginal stitch has failed.^[4]