RESUMEN
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.