What Is Cervical Incompetence?
The cervix is normally firm and closed during pregnancy, gradually softening and opening as labour approaches at term. Cervical incompetence (also called cervical insufficiency) refers to a cervix that opens or shortens prematurely — without the contractions of labour — typically in the second trimester. This can lead to pregnancy loss at 14–24 weeks or very early preterm birth.
Who Is at Risk of Cervical Incompetence?
- Previous second trimester pregnancy loss — particularly if sudden and painless
- Previous preterm birth before 34 weeks with no other explanation
- Short cervical length detected on mid-trimester ultrasound (<25mm before 24 weeks)
- Previous cervical procedures — LLETZ, cone biopsy, repeated dilatation
- Uterine abnormalities — bicornuate uterus
- Connective tissue disorders — Ehlers-Danlos syndrome
- Multiple pregnancy with short cervix
Types of Cerclage
- McDonald cerclage — a suture is placed around the cervix and tied; the most commonly performed type; performed vaginally at 12–14 weeks; removed at 36–37 weeks (or earlier if labour begins)
- Shirodkar cerclage — a deeper, more secure stitch placed higher on the cervix; technically more demanding but may be more effective in some cases
- Transabdominal cerclage (TAC) — placed at the cervicouterine junction via laparoscopy or open surgery; used when vaginal cerclage has failed or is not technically possible; the suture remains permanently and delivery must be by caesarean
Cervical Length Monitoring
Not all women with a short cervix need cerclage. Transvaginal cervical length monitoring between 16–24 weeks identifies women at risk. Progesterone supplementation is the first-line treatment for a short cervix in a singleton pregnancy without a history of preterm birth. Cerclage is added when progesterone alone is insufficient or when there is a strong history of cervical incompetence.