Clinical overview
Cervical cerclage is a surgical procedure in which a non-absorbable suture is placed around the cervix to provide mechanical support and resistance against premature cervical shortening and dilatation. It is one of the few interventions we have for the syndrome of preterm birth that targets a specific, identifiable mechanism: cervical insufficiency, in which the cervix shortens, effaces and dilates painlessly, often in the mid-trimester, leading to second-trimester loss or very preterm birth.
The exam framing of this objective is important. Cerclage is not a treatment for "threatened preterm labour" in general, and it is not a substitute for progesterone. It is a targeted intervention for a minority of women, and choosing the right woman is harder than performing the operation. Most registrars who get this objective wrong do so by over-applying cerclage (placing it where vaginal progesterone or expectant management would do as well or better) or by missing the small group in whom it genuinely changes the outcome. The three classic clinical situations — history-indicated, ultrasound-indicated, and physical-examination-indicated ("rescue") cerclage — each have different evidence, different urgency, and different risk profiles, and you must be able to distinguish them.
In the South African context, preterm birth is a major contributor to perinatal mortality, and the Saving Mothers / Saving Babies (NCCEMD) reporting consistently identifies immaturity-related deaths as a leading avoidable category. Cerclage is a procedure for the regional or tertiary level; the relevant decisions for a district-level practitioner are recognising the at-risk woman, referring appropriately, and not delaying when a cervix is found open. See Preterm birth and pprom and Progesterone in pregnancy for the wider preterm-prevention picture, and Recurrent pregnancy loss for the differential of mid-trimester loss.
Core knowledge
What "cervical insufficiency" is — and is not
Cervical insufficiency (the older term "incompetence" is discouraged) describes the inability of the cervix to retain a pregnancy in the absence of contractions or labour, classically presenting as painless cervical dilatation in the mid-trimester. It is best understood as one end of a continuum of cervical function rather than a discrete on/off defect. Cervical competence is a function of structural integrity (collagen, smooth muscle, the internal os), and is influenced by prior cervical trauma, congenital factors, and the same inflammatory and infective pathways that drive spontaneous preterm labour. This matters because cerclage addresses only the mechanical component; where infection or inflammation is the driver, a suture alone will not help and may even be harmful.
Recognised risk factors and associations include:
- Prior cervical surgery — large or repeated LLETZ/cone biopsy, mechanical dilatation; this is increasingly relevant in SA given the cervical-screening and CIN-treatment workload (see CIN management and Cervical screening SA).
- Prior mid-trimester loss or spontaneous preterm birth, particularly with a history of painless dilatation.
- Congenital factors — Müllerian anomalies, in-utero DES exposure (now rare), collagen disorders (e.g. Ehlers–Danlos).
- Prior obstetric trauma to the cervix.
The three types of cerclage by indication
| Type | Trigger | Timing | Evidence strength |
|---|---|---|---|
| History-indicated (elective) | Past history (≥3 mid-trimester losses / preterm births classically) | ~12–14 weeks, after viability scan | Benefit in a defined high-risk group |
| Ultrasound-indicated | Short cervix on TVS (singleton + prior spontaneous PTB) | When short cervix detected (typically 16–24 wk) | Reduces PTB in this subgroup |
| Physical-examination-indicated ("rescue") | Dilatation with exposed membranes on exam | Emergency, individualised | Lower-quality evidence; may prolong gestation |
Figure J15.1 — The three cervical cerclage indication pathways, with timing, triggers and inappropriate-use traps.
Surgical approaches
- Transvaginal cerclage is the default. Two techniques are described: the McDonald (a purse-string suture at the cervicovaginal junction, no bladder dissection, easily removable) and the Shirodkar (a higher suture placed after dissecting and reflecting the bladder, with the suture buried submucosally). The McDonald is technically simpler and is the more commonly used; there is no robust evidence that the Shirodkar is superior, and the standard teaching is that the two are broadly equivalent in outcome.
- Transabdominal cerclage places the suture at the level of the internal os via laparotomy or laparoscopy. It is reserved for women in whom a transvaginal suture has failed or is anatomically impossible (e.g. a very short or absent vaginal cervix after trachelectomy or extensive surgery). It commits the woman to caesarean delivery and to a second procedure (or leaving the suture in situ) for removal, and carries the additional morbidity of abdominal surgery.