Define and describe the causes, diagnosis and management of cervical Incompetence.

Painless dilatation without contractions is the hallmark.

Definition

Cervical incompetence (insufficiency) is the inability of the internal cervical os to retain the products of conception, causing painless progressive dilatation of the cervix in the mid-trimester and leading to recurrent second-trimester abortion or early preterm birth, owing to a functional or anatomical weakness of the internal os.

Cervical Incompetence - Approach

Causes

• Congenital — a constitutional weakness of the cervix, uterine anomalies, and prior diethylstilbestrol exposure.
• Acquired (traumatic) — the commonest: previous mechanical dilatation (dilatation and curettage, MTP), cervical amputation, conisation or extensive cautery, and obstetric cervical lacerations (precipitate labour, difficult instrumental delivery).

Diagnosis

• History (the cornerstone) — recurrent painless mid-trimester losses with a short, relatively painless labour and delivery of a live but pre-viable/immature fetus, often preceded by sudden rupture of the membranes.
• In the non-pregnant state — painless passage of a No. 8 Hegar dilator through the internal os, or a funnel-shaped internal os on hysterosalpingography.
• In pregnancy — transvaginal ultrasound showing a cervical length < 25 mm and/or funnelling of the internal os, with dilatation but without contractions.

Management

Cervical cerclage (encirclage)

A purse-string suture is placed around the cervix to reinforce the internal os.

• McDonald (simple purse-string at the cervico-vaginal junction) and Shirodkar (submucosal) are the common transvaginal techniques.
• Timing — an elective ("history/ultrasound-indicated") cerclage is placed at 12–14 weeks; a rescue (emergency) cerclage may be attempted with a dilating cervix and bulging membranes in the absence of infection/labour.
• Transabdominal cerclage is reserved for failed vaginal cerclage or an absent/scarred cervix.
• The suture is removed at about 37 weeks or earlier if labour starts, the membranes rupture, or infection supervenes (to avoid cervical tearing).

Adjuncts

Restriction of activity, vaginal progesterone (especially with a short cervix), a cervical pessary in selected cases, and treatment of any vaginal infection. Serial transvaginal ultrasound surveillance of cervical length (every 1–2 weeks in the mid-trimester) helps select women for an ultrasound-indicated cerclage and detects progressive shortening early.

Distinction from Preterm Labour

Cervical incompetence causes painless dilatation without uterine contractions, whereas preterm labour is accompanied by regular painful contractions with cervical change — a distinction that determines whether cerclage (rather than tocolysis and corticosteroids) is the appropriate treatment.

WHY the Cervix Fails Painlessly — and WHY That Is the Clue

The characteristic feature of cervical incompetence — and the key to diagnosing it — is why the pregnancy is lost without pain. In an ordinary miscarriage or preterm labour, the uterus contracts to expel the fetus, so the woman has painful contractions before anything is lost. In cervical incompetence the fault lies not in the uterus but in the cervix itself, whose fibromuscular ring is structurally weak — from previous obstetric or surgical injury (dilatation and curettage, cone biopsy, obstetric laceration) or a congenital collagen deficiency. As the pregnancy grows, the cervix is simply unable to bear the weight: it dilates and effaces silently under the load, the membranes bulge into the vagina, rupture, and the fetus is expelled — painlessly, rapidly, and typically as a live, normally-formed fetus in the mid-trimester (14–28 weeks). This gives the classic history: recurrent, painless mid-trimester losses, each at a similar or earlier gestation, with a live fetus. Recognising that painlessness and mid-trimester timing distinguish this from every other cause of pregnancy loss explains why the diagnosis rests chiefly on the history — and why it matters so much, since, uniquely among the causes of recurrent loss, it is mechanically correctable.

WHY Cerclage Works — and its Limits

Understanding why a stitch around the cervix can save a pregnancy, and when it must not be used, explains the treatment. Cerclage (the McDonald purse-string suture, simple and easily removed; or the Shirodkar suture, placed higher after dissecting the bladder) works by mechanically reinforcing the weak internal os, restoring its ability to bear the load. Its success depends on timing and selection. It is placed electively at 12–14 weeks — after the period of spontaneous first-trimester miscarriage (so that a doomed pregnancy is not stitched) but before the cervix begins to yield, and removed at about 37 weeks, or earlier if labour begins (leaving it in during labour would tear the cervix). It is contraindicated where there is infection or chorioamnionitis, active bleeding, ruptured membranes, a fetal anomaly or established labour — in these situations a stitch would trap infection or simply fail. An 'emergency' or rescue cerclage on an already-dilated cervix with bulging membranes has a much poorer prognosis. Understanding that cerclage is a mechanical solution to a mechanical problem — and useless where the problem is infection or contractions — explains both its impressive success in the right patient and its failure in the wrong one.

• Cervical incompetence: painless, progressive cervical dilatation causing recurrent mid-trimester (14–28 wk) loss of a live fetus.
• Causes: previous cervical trauma (D&C, cone biopsy, obstetric laceration) or congenital weakness; the history is the key to diagnosis.
• Diagnosis: classic history plus a short cervix (<25 mm) or funnelling on transvaginal ultrasound.
• Treatment: cervical cerclage (McDonald or Shirodkar) at 12–14 weeks; remove at 37 weeks or at the onset of labour.
• Contraindicated with infection, bleeding, ruptured membranes, fetal anomaly or established labour; vaginal progesterone is an alternative for a short cervix.