Aetiology

Cervical incompetence is congenital in up to 30% of women whose uterus has a congenital fundal abnormality or may result from exposure to diethyl-stilboestrol in utero.

The vast majority of cases, however, are acquired, most frequently as a result of trauma. For example:

• lateral cervical tears at the time of delivery
• cone biopsy for investigation of malignancy
• surgical dilation and evacuation for TOP - especially if dilated beyond 8-10 mm

Uncommonly, incompetence may be attributed to hormonal activity in pregnancy - the normal non-pregnant cervix may become incompetent as hormonal activity causes relaxation; to high collagenolytic activity producing a weak and distensible cervix; or to a low collagen-muscle ratio - the muscle excess compromising sphincter action.