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Health condition · Clinically reviewed

Incompetent cervix, cervical length, cerclage - and when specialist care changes outcomes.

A silent, mechanical cause of mid-trimester loss. With careful diagnosis and the right stitch or medicine, most pregnancies can be safely carried much further.

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Why trust this guide

  • 01

    Clinically reviewed

    Written by our editorial team and reviewed by a registered UK clinician before publication.

  • 02

    Sourced from guidance

    Checked against RCOG, FIGO and peer-reviewed obstetric sources you can see at the end.

  • 03

    Current for 2026

    Reflects modern UK guidance on cervical length screening, transvaginal cerclage and transabdominal options.

Key facts

Cervical insufficiency at a glance.

The essentials, in plain English - what it is, why it matters, and how it is treated in the UK today.

  • What it is

    Painless cervical dilatation in the second trimester - a mechanical cause of mid-trimester loss and preterm birth.

  • Also called

    Cervical insufficiency, cervical incompetence - the modern term is cervical insufficiency.

  • Why it matters

    Recurrent mid-trimester loss is preventable in most cases - accurate diagnosis unlocks effective treatment.

  • How it is spotted

    A previous second-trimester loss, a short cervix on transvaginal scan, or painless dilatation on examination.

  • Mainstay treatment

    Cervical cerclage - a stitch placed around the cervix - transvaginal or transabdominal, timed to the indication.

  • Adjuncts

    Vaginal progesterone, Arabin pessary in selected cases, and coordinated maternal-fetal medicine care.

Why this guide matters

A treatable, mostly preventable cause of loss.

The three points below shape everything else on this page - from who needs a scan to who needs a stitch.

  • History does most of the work

    Recurrent mid-trimester losses and previous cervical surgery point to insufficiency before any scan is done.

  • Transvaginal cervical length

    A cervical length under 25 mm between 16 and 24 weeks is the recognised threshold for specialist review.

  • Cerclage changes outcomes

    History, ultrasound and rescue cerclage each have a place - the right one at the right time saves pregnancies.

How the diagnosis is made

From history to a clear specialist plan.

The steps a UK obstetric team and maternal-fetal medicine specialist will normally follow, in order - so you know what to expect and why.

  1. 01

    Assessing

    Obstetric and surgical history

    Previous mid-trimester losses, spontaneous preterm births, LLETZ or cone biopsies, DES exposure and connective tissue disorders.

  2. 02

    Assessing

    Red flag review

    Painless pressure, watery discharge, spotting or a sensation of something in the vagina between 16 and 24 weeks needs same-day review.

  3. 03

    Assessing

    Speculum and gentle examination

    To look for cervical dilatation, effacement or prolapsed membranes - handled carefully to avoid rupture.

  4. 04

    Confirming

    Transvaginal cervical length

    The reference test between 16 and 24 weeks - a length under 25 mm is the recognised threshold for concern.

  5. 05

    Confirming

    Serial scans in high risk

    Fortnightly transvaginal scans from 14 to 24 weeks in women with previous mid-trimester loss or major cervical surgery.

  6. 06

    Preparing

    Specialist referral

    Maternal-fetal medicine input at a specialist commissioned high-risk pregnancy centre to plan cerclage or medical treatment.

  7. 07

    Preparing

    MDT plan and consent

    Choice of cerclage technique, timing, progesterone, steroids for lung maturity and clear escalation triggers - all agreed together.

Typical timeline: from first booking visit to a settled specialist plan within a few weeks.

Symptoms and signs

What cervical insufficiency actually looks like.

It can be quiet, which is why the pattern of previous pregnancy loss and a transvaginal scan matter so much.

  • Painless dilatation

    Silent cervical opening without contractions - the hallmark sign in the mid-trimester.

  • Pressure or heaviness

    A dull pelvic pressure or bearing-down sensation between 16 and 24 weeks needs same-day review.

  • Watery or pink discharge

    A change in vaginal discharge - watery, mucus-like or blood-stained - can precede membrane exposure.

  • Short cervix on scan

    A transvaginal cervical length under 25 mm in the mid-trimester is the recognised threshold for action.

  • Prolapsed membranes

    Visible or ballooning membranes at the external os - an urgent finding, usually managed with rescue cerclage.

  • Recurrent mid-trimester loss

    Three or more second-trimester losses is the classic history-indicated pattern for elective cerclage.

  • Previous cervical surgery

    LLETZ, cone biopsy or repeated dilatation - a risk factor for insufficiency, worth flagging early in pregnancy.

  • Red flag - bleeding or fluid loss

    Fresh bleeding, gushing fluid or ruptured membranes at any gestation needs emergency obstetric review.

Treatment

How cervical insufficiency is treated in the UK.

A stepped, indication-led plan - transvaginal cerclage first for most, transabdominal cerclage or medical options where those are right.

  • History-indicated cerclage

    Elective transvaginal stitch at 12 to 14 weeks for women with three or more mid-trimester losses or preterm births.

  • Ultrasound-indicated cerclage

    For high-risk women with a cervical length under 25 mm on transvaginal scan before 24 weeks - specialist-led decision.

  • Rescue cerclage

    For dilated cervix with bulging or exposed membranes - a specialist commissioned emergency stitch to prolong pregnancy.

  • Transabdominal cerclage

    For failed transvaginal cerclage or a very short residual cervix - open or laparoscopic, at a specialist commissioned centre.

  • Vaginal progesterone

    Nightly pessary for women with a short cervix - reduces preterm birth risk, often alongside or instead of cerclage.

  • Arabin cervical pessary

    A soft silicone ring that supports the cervix - used selectively where cerclage or progesterone are unsuitable.

  • Antenatal steroids

    A course of steroid injections between 24 and 34 weeks accelerates fetal lung maturity if preterm birth looks likely.

  • Specialist MDT care

    Coordinated maternal-fetal medicine, obstetrics, midwifery and neonatology at a high-risk pregnancy centre.

What this guide is based on

The sources behind every claim on this page.

UK national guidance and specialist society standards, current at the time of last review.

Key references

Guidelines and standards we relied on.

A quiet reminder

This guide is for information, not medical advice.

Your obstetric team and maternal-fetal medicine specialist know your history and can tell you which parts apply to you. If in doubt, get seen.

  • Royal College of Obstetricians and Gynaecologists (RCOG). Green-top Guideline 60: Cervical Cerclage.

  • International Federation of Gynecology and Obstetrics (FIGO). Best practice in maternal-fetal medicine.

  • NICE. Preterm labour and birth (NG25).

  • NHS. Miscarriage and pregnancy loss information for patients.

Red flags

When to phone triage immediately.

Any of these in pregnancy needs same-day obstetric assessment - not a wait-and-see appointment.

  • Ruptured membranes

    A gush or steady leak of fluid at any gestation needs emergency obstetric review - avoid tampons and go straight in.

  • Vaginal bleeding

    Fresh bleeding in pregnancy is never normal - triage on the same day, urgently if heavy or with pain.

  • Pelvic pressure between 16 and 24 weeks

    A bearing-down sensation or feeling of something in the vagina is a classic warning of silent dilatation.

  • Prolapsed membranes on examination

    Visible membranes at the external os - a specialist commissioned emergency, often managed with rescue cerclage.

  • Signs of infection with a stitch in

    Fever, foul discharge or uterine tenderness after cerclage - urgent review, the stitch may need removal.

  • Preterm labour after cerclage

    Regular painful tightenings before 37 weeks - the cerclage is usually removed before labour progresses.

Living with it

A high-risk pregnancy, managed with a plan.

Four things that make the biggest difference through the second and third trimester - a written plan, symptom awareness, specialist follow-up and support for the mental load.

A quiet reminder

You are not being over-cautious.

After a loss, every twinge feels loud. Ring triage, get scanned - a normal result is worth the trip.

  1. 01 Plan

    Agree a written plan

    Timing of cerclage, scan intervals, progesterone and escalation triggers - written down and shared with your team.

  2. 02 Watch

    Know the warning signs

    Pelvic pressure, watery discharge, spotting or a change in movements after viability - phone triage the same day.

  3. 03 Care

    Keep specialist appointments

    Serial transvaginal scans and MFM reviews catch changes early - never a wasted visit in a high-risk pregnancy.

  4. 04 Support

    Look after the mental load

    Recurrent loss is heavy - specialist counselling, peer support and honest conversations with your team all help.

Frequently asked

Everything we get asked about cervical insufficiency.

Quick answers on causes, cervical length, cerclage options and progesterone.

  • What is an incompetent cervix?

    Cervical insufficiency, sometimes still called an incompetent cervix, is painless dilatation of the cervix in the second trimester. It can cause mid-trimester pregnancy loss and preterm birth, and it is usually diagnosed from previous obstetric history, a short cervix on transvaginal scan or painless dilatation on examination.

  • What causes cervical insufficiency?

    Causes are congenital, such as uterine anomalies or connective tissue disorders like Ehlers-Danlos syndrome, or acquired after cervical surgery (LLETZ, cone biopsy), obstetric trauma or DES exposure. In many women no single cause is found and the diagnosis is made from the pattern of pregnancy loss.

  • How is it diagnosed?

    By a careful history of previous mid-trimester losses or preterm births, transvaginal cervical length measurement between 16 and 24 weeks, and speculum examination when symptoms suggest dilatation. A cervical length under 25 mm in the mid-trimester is the recognised threshold for specialist review.

  • What is a cervical cerclage?

    A cerclage is a stitch placed around the cervix to help it hold a pregnancy. It can be history-indicated at 12 to 14 weeks, ultrasound-indicated for a short cervix, or a rescue procedure for a dilated cervix with exposed membranes. Techniques include McDonald and Shirodkar transvaginal stitches, and transabdominal cerclage for selected cases.

  • When is transabdominal cerclage used?

    When a previous transvaginal cerclage has failed, or when there is no accessible cervical tissue after major cervical surgery. It is performed at specialist commissioned centres, either as an open procedure or laparoscopically, and delivery is then by planned caesarean section.

  • Does progesterone help?

    Vaginal progesterone reduces the risk of preterm birth in women with a short cervix on transvaginal scan. It is often used alongside or instead of cerclage, guided by a maternal-fetal medicine specialist and the specific pattern of risk.

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