What is cervical incompetence?
Cervical incompetence (now usually called cervical insufficiency) is the inability of the cervix to retain a pregnancy in the absence of uterine contractions — that is, painless cervical dilatation in the second or early third trimester caused by a functional or structural defect of the cervix. It can lead to second-trimester loss, PPROM or spontaneous preterm birth, and is often diagnosed only in retrospect.
| Type | Examples |
|---|---|
| Congenital (uncommon) | Müllerian duct anomalies; collagen disorders such as Ehlers-Danlos syndrome; in-utero diethylstilbestrol (DES) exposure |
| Acquired (most common: cervical trauma) | Cervical lacerations at delivery (precipitate birth, prolonged second stage); cone biopsy / conization, LEEP (LLETZ); repeated mechanical dilatation such as D&C |
How is cervical incompetence diagnosed?
There is no single test. StatPearls lists three routes to the diagnosis, which map directly onto the three types of cerclage:
- History — previous second-trimester losses or preterm births related to painless dilatation.
- Ultrasound — a short cervix (less than 25 mm) on transvaginal scan before 24 weeks.
- Physical examination — painless cervical dilatation without labour, sometimes with membranes visible at the os.
Women with a previous spontaneous preterm birth are screened with serial transvaginal cervical length scans — StatPearls describes scans every 1–2 weeks between 16 and 24 weeks; the RCOG leaflet describes scans between 16 and 22 weeks. The transvaginal route is the standard for measuring cervical length.
The RCOG leaflet lists who should be referred early to a specialist preterm-birth clinic: a previous miscarriage after 16 weeks; a previous birth before 34 weeks; waters breaking before 34 weeks in a previous pregnancy; LLETZ or cone biopsy; endometrial scarring or an abnormally shaped uterus; a previous caesarean at full dilatation; and a cervical stitch in any previous pregnancy. These women are offered either a planned (history-indicated) stitch or scan surveillance.
What are history-, ultrasound- and examination-indicated cerclage?
| Type | Who gets it | Timing |
|---|---|---|
| History-indicated (prophylactic, elective) | ACOG: one or more second-trimester losses related to painless dilatation (in the absence of labour or abruption), or a previous exam-indicated cerclage. RCOG and SOGC: generally after 3 or more second-trimester losses or preterm births | 12–14 weeks |
| Ultrasound-indicated | Singleton pregnancy, previous spontaneous preterm birth or second-trimester loss, cervical length below 25 mm before 24 weeks | Before 24 weeks |
| Physical examination-indicated (emergency, rescue) | Painless cervical dilatation without contractions, infection or abruption | Before 24 weeks (StatPearls also cites use up to 28 weeks with 1–4 cm dilatation) |
Exam-indicated cerclage carries the most risk but also the biggest relative gain: observational studies quoted by StatPearls show it prolongs pregnancy by about 6–9 weeks, compared with less than 4 weeks with expectant management. Initial dilatation greater than 4 cm is associated with a poor prognosis.
How do McDonald, Shirodkar and abdominal cerclage differ?
| Feature | McDonald | Shirodkar | Transabdominal (TAC) |
|---|---|---|---|
| Route | Transvaginal | Transvaginal | Abdominal — open or laparoscopic |
| Technique | Purse-string non-absorbable suture at the cervicovaginal junction, as high as possible; no dissection | Vaginal mucosa incised; bladder (and rectum) reflected so the suture lies higher, near the internal os | Suture placed higher around the cervix through the abdomen |
| Ease of placement and removal | Easiest — knot usually tied anteriorly; removed in clinic | More dissection; removal harder | Not removed vaginally |
| Delivery | Vaginal birth after removal | Vaginal birth after removal | Caesarean; stitch usually left for future pregnancies |
| When chosen | Most cerclages | When a higher vaginal stitch is wanted | Failed vaginal cerclage or no cervix to stitch vaginally; can be placed before conception |
StatPearls notes that studies show comparable efficacy of the McDonald and Shirodkar techniques, so the McDonald is generally preferred because it is easier to place and remove. Transabdominal cerclage has higher morbidity, partly because delivery must be by caesarean, so the vaginal route is preferred in pregnancy where possible.
When is cerclage contraindicated and what are its risks?
- Contraindications (StatPearls): active preterm labour, PPROM, placental abruption, intra-amniotic infection, fetal demise, and fetal anomalies incompatible with life.
- Do an obstetric ultrasound before placing a cerclage to confirm viability and gestational age and to exclude major anomalies.
- Multiple pregnancy on its own is not an indication for cerclage (or for vaginal progesterone).
- Risks: infection or sepsis, rupture of membranes, cervical lacerations, anaesthetic complications; ultrasound- and exam-indicated stitches carry more risk than history-indicated ones.
How is a cerclage performed and followed up?
- Confirm viability, gestational age and the absence of major anomalies on ultrasound; exclude labour, infection and bleeding.
- Give regional (spinal) or general anaesthesia; the patient lies in the dorsal lithotomy position and the vagina is prepared.
- Expose the cervix with a speculum or retractors and place a non-absorbable suture around it (McDonald purse-string or Shirodkar after bladder dissection). The RCOG leaflet notes the operation takes less than one hour and antibiotics may be given during it.
- Discharge with advice to return for fever, abdominal pain, cramping or contractions, leaking fluid or vaginal bleeding.
StatPearls notes no proven benefit from routine post-cerclage cervical length surveillance. In a randomised trial of ultrasound-indicated cerclage (previous preterm birth and cervix below 25 mm), the stitch reduced previable birth from 14% to 6.1% and perinatal death from 16% to 8.8%.
When is a cervical cerclage removed?
| Situation | Action |
|---|---|
| Uncomplicated vaginal cerclage | Remove at 36–37 weeks (RCOG); StatPearls quotes 36–38 weeks — before the onset of labour, usually in clinic without anaesthesia |
| Preterm labour | Remove immediately — contractions against a stitch can tear the cervix |
| Sepsis or chorioamnionitis | Remove |
| PPROM without labour | Usually removed because of infection risk; StatPearls (SOGC) advises within 48 hours |
| Planned caesarean | Removal may be deferred until the caesarean |
| Abdominal cerclage | Not removed; delivery by caesarean, stitch left for future pregnancies |
What is the role of vaginal progesterone?
Progesterone is thought to suppress myometrial contractility and inflammatory pathways and to affect cervical remodelling. According to StatPearls, vaginal progesterone reduces preterm birth in:
- Women with an incidental short cervix (below 25 mm) and no previous preterm birth — the main indication; cerclage adds no benefit when the cervix is 10–25 mm in this group.
- Women with a previous preterm birth and a cervix below 25 mm — as an alternative or adjunct to ultrasound-indicated cerclage.
Typical regimens are 200 mg micronised progesterone vaginal capsules or 90 mg of 8% vaginal gel daily; the RCOG leaflet describes progesterone pessaries used daily until 34 weeks. In a meta-analysis of women with a short cervix and no other risk factors, vaginal progesterone lowered preterm birth before 34 weeks from 24.6% to 14.5%. StatPearls also reports that 17-hydroxyprogesterone caproate is ineffective in reducing recurrent preterm birth.
Related reading: amniotic fluid (PPROM and infection), antepartum haemorrhage (abruption as a contraindication) and physiological changes of pregnancy.