CERVICAL FUNNELING (EFFACEMENT)

Cervical funneling is the opening of the internal cervical os with protrusion of the amniotic sac into the cervical canal.

Cervical funneling can be assessed with either translabial or transvaginal scanning (inducing undue pressure on the anterior cervix by the endovaginal probe may increase cervical length). Translabial (transperineal) scanning avoids problems associated with probe pressure, but image clarity, especially at the external cervical os is limited. Funneling may be present transiently in normal pregnancies and at risk pregnancies, and may require patience to elicit. Funneling disappears as the cervix shortens (usually absent when cervix is < 2cm).

• Dynamic process that begins at the internal cervical os and proceeds caudally to the external cervical os.
• Internal os may open and close in the absence of a palpable uterine contraction.
• Shape of effacement is; Y, U, V, or Y.
• Funneling is probably normal after 32 weeks.

RISK OF PRETERN BIRTH

• Likelihood increases as cervical length decreases at 24-28 weeks.
• Risk increases when length decreases to 25-30mm (10th and 25th percentile).
• < 25% funneling, risk of preterm delivery = 17%.
• 25-50% funneling, risk of preterm delivery = 29%.
• > 50% funneling, risk of preterm delivery = 79%.
• Cervix ³ 30mm - No active labor.
• Cervix £ 20mm or funneling 40-50% is an excellent positive predictor of preterm labor.
• Cervix 20-30mm and small funnel <30% - increased risk but may / may not be in active labor.
• Fetal fibronectin assay (marker for disturbed fetal - maternal interphases). Slightly better than any single ultrasound in predicting preterm labor).