Changes in cervical length and the risk of preterm labor

OBJECTIVE: The purpose of this study was to assess the value of cervical length change as a predictor of preterm labor. STUDY DESIGN: We used an historic cohort of 154 women to compare change in cervical length and preterm birth. Independent variables included cervical length at the first sonogram, absolute change of cervical length, and change per unit time. Covariates included age, parity, and history of preterm birth. Eligible patients had 2 or more sonograms that included cervical length. RESULTS: The risk of preterm delivery increased as the length of the cervix declined, after an adjustment was made for the initial cervical length (P < .05). There were no significant interactions between initial length and the change of length; however, the highest rate of preterm deliveries occurred among women with a cervical length <3 cm at the first sonogram (23%). If the change in cervical length was expressed as a unit equal to a decline of 1 cm per month, the odds of giving birth to a preterm baby were 6.8-fold greater per unit change (P < .05). CONCLUSION: A cervical length of <3 cm before 16 weeks of gestation is associated strongly with preterm birth; independently of baseline length, more rapid shortening of the cervix increases the risk of preterm birth.