Scar Thickness Measurement by Transvaginal Sonography in Late Second Trimester and Third Trimester in Pregnant Patients with Previous Cesarean Section: Does Sequential Change in Scar Thickness with Gestational Age Correlate with Mode of Delivery?

Purpose: The objective of this study was to evaluate whether scar thickness measured by transvaginal sonography and the sequential change in scar thickness from second to third trimester has any association with mode of delivery in patients with previous cesarean.

Methods: Pregnant women with previous one cesarean section underwent transvaginal sonography between 24 and 28 weeks of gestation and then a repeat scan beyond 36 weeks of gestation to measure scar thickness. These scar thickness measurements were then correlated with the mode of delivery. The scar was measured at multiple sites (3-4) of the lower uterine segment and its thinnest portion was considered to be the scar.

Result: Scar thickness was thinner in those patients having cesarean delivery than those having vaginal delivery and this difference was statistically significant at both the gestational ages. Mean scar thickness at 24-28 weeks of gestation in patients who delivered vaginally is 4.8 ± 1.1 mm and in those who had repeat cesarean section is 4.4 ± 1.1 mm (p value = 0.043). Mean scar thickness beyond 36 weeks of gestation in patients who delivered vaginally is 3.3 ± 0.7 mm and in those who had repeat cesarean section is 2.9 ± 0.9 mm (p value = 0.003). The mean decrease in scar thickness was not significantly different between those who delivered vaginally (mean decrease = 1.73 ± 0.95 mm) and those who had a repeat cesarean (mean decrease = 1.91 ± 0.96 mm).

Conclusion: Our study concluded that thicker scars are associated with better chances of successful vaginal birth after cesarean. Measurement at both late second trimester and third trimester can be done but latter has better correlation with mode of delivery. This association may be explained by the fact that thinner scars have more chances of fetal bradycardia, meconium staining of liquor and previous cesarean for feto-pelvic disproportion.