1. Cervical length, measured by transvaginal ultrasound, was moderately useful at predicting time to spontaneous labor in a term pregnancy.
2. A woman with a cervical length of 10 mm had over an 85% chance of delivering within one week.
Evidence Rating Level: 1 (Excellent)
Study Rundown: One of the most common questions a pregnant woman asks her Ob-Gyn is “when will I deliver?”, and this question becomes even more popular as the expected due date gets closer. Currently, the best practice for estimating gestational age and due date uses a combination of last menstrual period and early ultrasound size, but this method is only perfectly accurate 5 percent of the time. With the increasing availability of ultrasound, cervical length has become easier to measure, and much research has focused on it’s clinical. There is robust evidence linking cervical length to risk of preterm delivery, however studies looking at its use in other settings have been more limited. In this systematic review and meta-analysis, researchers combined the findings of five studies to evaluate the accuracy of cervical length in women at term (37-40 weeks) as a predictor of spontaneous delivery within one week.
Cervical length, measured by transvaginal ultrasound, was moderately useful at predicting time to spontaneous labor in a term pregnancy. A woman with a cervical length of 30 mm had less than a 50 percent chance of delivering within one week, where as a woman with a cervical length of 10 mm had more than an 85 percent chance. This is the first meta-analysis to look at the capacity of cervical length at term to predict time to spontaneous labor. A limitation of this analysis is since none of the studies included stratified data by parity or gestational age, subgroup analyses weren’t feasible. Moreover, they only looked at term, vertex presenting, singleton pregnancies, so the findings may not be generalizable. Future studies could try to repeat these findings in a wider variety of pregnancies, including breech presentations, multiple gestations, and a variety of gestational ages.
In-Depth [meta-analysis]: Researchers performed a systematic review of the literature for randomized controlled trials, case-control and cohort studies that looked at transvaginal ultrasound cervical length as a predictor of spontaneous onset of labor in vertex presenting, singleton gestations at term (≥37 weeks gestation). Results were pooled. The primary outcome was accuracy of cervical length at term to predict spontaneous labor within 7 days.
Five studies with a total of 735 gestations were included in the meta-analysis. A cervical length of <30 mm had a 65% sensitivity (95%CI 58-69%) and a 60% specificity (95%CI 55-65%)for predicting spontaneous labor within 7 days. There was a strong inverse linear relationship between cervical length and positive predictive value (R2 = 0.9898)— a woman with a cervical length of 30 mm had a 41% likelihood of delivering within one week while a cervical length of 10 mm had an 85% likelihood.
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