Cervical Effacement in Pregnancy: Definition, Measurement, and Labor Prediction Value

Definition

Effacement refers to the shortening and thinning of the cervix from ~3–4 cm long to paper-thin (0 cm), expressed as a percentage (0% = long/closed, 100% = fully effaced).

Physiology

• Driven by prostaglandin-mediated collagen breakdown and uterine contractile forces.
• Often precedes dilation in nulliparas; may occur simultaneously in multiparas.

Clinical Assessment

• Digital exam (subjective, inter-observer variability).
• Transvaginal ultrasound (cervical length <25 mm at <24 weeks predicts preterm birth).

Predictive Value for Labor Onset

• High effacement (80–100%) + dilation ≥2 cm: Labor likely within days (especially with contractions).
• Effacement alone: Poor predictor—can persist for weeks without labor.
• Combined with fetal fibronectin, cervical length, contraction pattern: Improves specificity.

Patient Counseling

Reassure that effacement is a normal preparatory process. Encourage monitoring for regular contractions (≥6/hr), rupture of membranes, or bleeding—not effacement percentage alone.