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Cervical Length and Cesarean Delivery

Longer midpregnancy cervical length was an independent predictor of higher cesarean delivery rates at term.

Poor progress during labor (dystocia) is the main indication for primary cesarean delivery. Building on prior observations that the cervix undergoes preparative changes before labor and that women with short cervices are at risk for preterm birth, U.K. investigators conducted a secondary analysis of a multicenter cohort of more than 27,000 primiparous women to assess whether women with long cervices are more likely to require cesarean delivery at term. Participants underwent cervical-length measurement by transvaginal ultrasound examination at a median 23 weeks’ gestation. Pregnancy outcomes were obtained from hospital delivery records.

Longer midpregnancy cervical length was an independent predictor of higher cesarean delivery rates at term: In analysis adjusted for many factors (e.g., maternal age, BMI, smoking status, race or ethnicity, induced or spontaneous labor, and birth-weight percentile), women in the highest quartile for cervical length (40–67 mm) were 1.68 times as likely as women in the lowest quartile for cervical length (16–30 mm) to undergo cesarean delivery (P<0.001). Cesarean rates began to rise at a cervical length of 25 mm and leveled off at a cervical length of 50 mm. The authors suggest that this increased rate was attributable to dystocia.

Comment: Just as short cervical lengths are associated with risk for spontaneous preterm labor, these results suggest that particularly long cervical lengths are associated with ineffective labor. Notably, the authors could not detail cervical changes during late pregnancy or labor, nor could they eliminate the possibility of residual confounding. As is typical with ultrasound studies, intraobserver variation was not documented. In addition, no mention is made of the normal distribution of cervical lengths at different times during pregnancy. These findings should not change current obstetric practice for labor; indeed, given that this observation might be unrelated to risk for cesarean delivery, women need not be warned.

— Sandra Ann Carson, MD

Published in Journal Watch Women's Health March 26, 2008

Citation(s):

Smith GCS et al. Cervical length at mid-pregnancy and the risk of primary cesarean delivery. N Engl J Med 2008 Mar 27; 358:1346.

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