Prognostic Value of Post-Cerclage Transvaginal Ultrasound Parameters in Predicting Spontaneous Preterm Birth

Background and Objectives: Preterm birth (PTB) remains a leading cause of neonatal morbidity and mortality worldwide, particularly among women with cervical insufficiency. This study aimed to identify whether transvaginal sonographic parameters assessed following McDonald cerclage could act as predictors for the risk of spontaneous PTB < 34 weeks. Materials and Methods: A cohort of singleton pregnancies without structural abnormalities that underwent McDonald cerclage and had at least one transvaginal ultrasound (TVUS) examination between 16-25 weeks' gestation was retrospectively analyzed. Two blinded reviewers evaluated the images. Measurements included total cervical length, cervical lengths above and below the stitch, anterior and posterior cervical widths at the suture level, as well as anterior and posterior stitch depths. Additionally, the angle between the cervical canal and the anterior uterine wall was assessed at both the internal and external os. Presence of funneling and intra-amniotic sludge was also noted. Maternal demographic and obstetric data were collected, and ultrasound findings were compared between women who delivered before and after 34 weeks. Results: A total of 45 women were enrolled, with cerclage indications categorized as history-based (76%), ultrasound-based (9%) or exam-based (15%). Overall, PTB < 34 weeks occurred in 38% (n = 17). Maternal characteristics did not vary between groups. However, both total cervical length and cervical length above the stitch were significantly shorter in women with PTB < 34 weeks vs. PTB ≥ 34 (27.60 ± 8.81 mm vs. 35.89 ± 7.09 mm, p = 0.012; and 13.15 ± 9.17 mm vs. 21.87 ± 8.95 mm, p = 0.004, respectively). Funneling beyond the cerclage was observed exclusively in women who delivered < 34 weeks (29.4%, p = 0.005). Funneling at the internal os (58.8% vs. 3.6%, p < 0.001) and intra-amniotic sludge (29.4% vs. 3.6%, p = 0.023) were likewise more frequent in this group. Conclusions: In addition to cervical length measurement, post-cerclage transvaginal ultrasound-through the evaluation of suture position, cervical funneling, and intra-amniotic sludge-may assist in identifying women at higher risk of PTB < 34 weeks.