Comparative longitudinal study of cervical length and induced shortening changes among singleton, twin, and triplet pregnancies.

Objective: To compare cervical length and induced shortening changes during gestation among singleton, twin, and triplet pregnancies.

Study Design: Thirty-two healthy gravidas (12 singleton, 13 twin, and 7 triplet pregnancies) between 17 and 20 weeks' gestation were prospectively enrolled in this longitudinal investigation of cervical length. Serial transperineal cervical length ultrasound assessments were made weekly until 34 weeks' gestation under 3 conditions: 1) supine, 2) supine with the Valsalva maneuver, and 3) standing.