1. Women who achieved vaginal birth after cesarean (VBAC) were more likely to have a shorter 2nd trimester cervical length.
2. The addition of cervical length did not improve predictive models for VBAC.
Evidence Rating Level: 2 (Good)
Study Rundown: As the number of cesarean deliveries (CD) continues to increase in many parts of the world, more women are considered for a trial of labor after cesarean (TOLAC). Previously, women who underwent CD routinely underwent elective repeat cesareans for subsequent pregnancies. However, successful TOLAC is associated with lower rates of maternal and neonatal morbidity than repeat cesarean. In contrast, failed TOLAC is associated with greater risk of complications such as uterine rupture, infection and perinatal death. Thus candidates for TOLAC must be evaluated carefully. Factors associated with successful TOLAC or vaginal birth after cesarean (VBAC) include one prior low transverse uterine incision, previous VBAC and spontaneous labor. Prior studies have shown that sonographic 2nd trimester cervical length (CL) is associated with obstetric complications whereby shorter CL is associated with preterm birth and longer CL is associated with labor dystocia and CD. Here, authors evaluated whether CL is a useful predictor of VBAC. Results demonstrate that while shorter CL in the 2nd trimester was associated with an increased likelihood for VBAC, it contributed no additional predictive value to known predictors.
Strengths of the study include a diverse patient population and comparison to a predictive model of characteristics known to be associated with VBAC. Limitations include retrospective design and unknown inter- and intra-observer variability for CL measurements. Prospective studies are needed to further evaluate inclusion of CL in predictive models for successful TOLAC.
Click to read the study in AJOG
Relevant Reading: Development of a nomogram for prediction of vaginal birth after cesarean delivery
In-Depth [retrospective cohort]: This study explored the utility of sonographic 2nd trimester cervical length measurement as a predictor of successful TOLAC in women who went on to experience VBAC (n=517) and those who failed TOLAC (n=161). The primary predictor of interest was CL during the 2nd trimester; other measured predictors included maternal age, BMI, race/ethnicity, and prior birth history.
Women who successfully delivered vaginally had a shorter mean cervical length (p<0.001). Each additional centimeter in length was associated with 40% reduced odds of achieving VBAC. The area under curve was greater for the model including CL (p=0.03) but inclusion of CL did not improve classification of patients as low, intermediate or high chance of VBAC.
Image: PD
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