Routine anomaly scan at 21/40.
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A sagittal transvaginal ultrasound image of the cervix at 21 weeks gestation shows funnelling of the proximal cervix, and reduction of the functional length to 10 mm.
Cervical incompetence is variably defined, however a cervical length of <25 mm is often used. The risk of preterm delivery is inversely proportional to cervical length - 18% for <25mm and 25% for <20mm.
The presence of funnelling is important. Greater than 50% funnelling before 25 weeks is associated with 80% risk of preterm delivery. Patients at high risk for preterm delivery include:
- uterine anomalies
- previous cervical trauma or surgery
- history of recurrent spontaneous or therapeutic abortion
- history of preterm (<32 weeks) birth
Transvaginal sonography is most commonly used to assess the cervix, however translabial and transperineal techniques have been used.
Management is controversial, with conflicting results, particularly regarding the efficacy of cerclage. Bed-rest, tocolysis, cerclage, and administration of steroids to accelerate fetal lung maturity are all treatment options to be considered. A recent metaanalysis suggests that cerclage is effective in reducing preterm births by 26% in singleton pregnancies.