Ultrasound evaluation of uterine scar thickness after open fetal surgery for myelomeningocele

Purpose This study aimed to analyse the evolution of uterine scar thickness after open fetal surgery for myelomeningocele (MMC) by ultrasonography, and to establish a cut-off point for uterine scar thickness associated with high-risk of uterine rupture. Methods A prospective longitudinal study was conducted with 77 pregnant women who underwent open fetal surgery for MMC between 24 and 27 weeks of gestation. After fetal surgery, ultrasound follow-up was performed once a week, and the scar on the uterine wall was evaluated and its thickness was measured by transabdominal ultrasound. At least five measurements of the uterine scar thickness were performed during pregnancy. A receiver operating characteristics (ROC) curve was constructed to obtain a cut-off point for the thickness of the scar capable of detecting the absence of thinning. Kaplan-Meier curves were constructed to evaluate the probability of thinning during pregnancy follow-up. Results The mean +/- standard deviation of maternal age (years), gestational age at surgery (weeks), gestational age at delivery (weeks), and birth weight (g) were 30.6 +/- 4.5, 26.1 +/- 0.8, 34.3 +/- 1.2 and 2287.4 +/- 334.4, respectively. Thinning was observed in 23 patients (29.9%). Pregnant women with no thinning had an average of 17.1 +/- 5.2 min longer surgery time than pregnant women with thinning. A decrease of 1.0 mm in the thickness of the uterine scar was associated with an increased likelihood of thinning by 1.81-fold (95% confidence interval [CI]: 1.32-2.47; p < 0.001). The area below the ROC curve was 0.899 (95% CI: 0.806-0.954; p < 0.001), and the cut-off point was <= 3.0 mm, which simultaneously presented greater sensitivity and specificity. After 63 days of surgery, the probability of uterine scarring was 50% (95% CI: 58-69). Conclusion A cut-off point of <= 3.0 mm in the thickness of the uterine scar after open fetal surgery for MMC may be used during ultrasonography monitoring for decision-making regarding the risk of uterine rupture and indication of caesarean section.