After having a previous cesarean delivery (CD), women who subsequently become pregnant inevitably face the decision to undergo a repeat CD or attempt a trial of labor after cesarean (TOLAC). Currently in the United States, 83% of women with a prior uterine scar are delivered by repeat CD.1 According to the Consortium on Safe Labor, more than half of all CD indications are attributed to having a prior uterine scar.1 Furthermore, only 28% of women attempt a TOLAC, with a successful vaginal birth after cesarean (VBAC) rate of approximately 57%.1
The reason for the low TOLAC rate is multifactorial, but a primary concern may be the safety risk of a TOLAC as it relates to uterine rupture, a rare but potentially catastrophic complication. In a large, multicenter prospective observational trial of more than 17,800 women attempting a TOLAC, the symptomatic uterine rupture rate was 0.7%.2 As such, efforts to identify women at highest risk for uterine rupture and those with characteristics predictive of a successful VBAC have remained ongoing. Jastrow and colleagues have expanded this body of knowledge with their prospective cohort study.
Details of the study
The researchers assessed lower uterine segment thickness via vaginal and abdominal ultrasound at 34 to 38 weeks’ gestation in more than 1,850 women with a previous CD. Women enrolled in the trial were classified into 3 risk categories based on lower uterine segment thickness: high risk (<2.0 mm), intermediate risk (2.0 to 2.4 mm), and low risk (≥2.5 mm). The investigators’ objective was to estimate the occurrence of uterine rupture when this measurement was included in the decision-making process on mode of delivery.
An important aspect of this study involved how the provider discussed the mode of delivery with the patient after the lower uterine segment measurement was obtained. Both the provider and the patient were informed of the risk category, and further counseling included the following:
- average overall uterine rupture risk, 0.5% to 1%
- if <2.0 mm, uterine rupture risk likely >1%
- if ≥2.5 mm, uterine rupture risk likely <0.5%
- uterine rupture risks (including perinatal asphyxia and death)
- maternal and neonatal complications of cesarean
- estimation of likelihood for successful VBAC.
How did risk-stratified women fare?
In approximately 1,000 cases, the authors reported no symptomatic uterine ruptures. Of particular interest, however, is the rate of women attempting a TOLAC in each category:
- 194 women with high risk
- 9% underwent a TOLAC
- 82% had a successful vaginal birth
- 217 women with intermediate risk
- 42% underwent a TOLAC
- 78% had a successful vaginal birth
- 1,438 women with low risk
- 61% underwent a TOLAC
- 66% had a successful vaginal birth.
Considering cesarean scar defect
Finally, uterine scar defects at CD in those who underwent a TOLAC were 0/3 (0%), 5/21 (25%), and 20/276 (7%) in the high-, intermediate-, and low-risk groups, respectively. Given the observational nature of the study, the authors suggest that uterine scar dehiscence may be predictive of labor dystocia, but it remains unclear if it predicts or is a prerequisite for subsequent uterine rupture if labor occurs.
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