Can transvaginal and transabdominal cervical length measurements at 37 weeks predict the risk of prolonged pregnancy?

OBJECTIVE

To evaluate the role of transvaginal and transabdominal cervical length (CL) measurements at 37 weeks of gestation in predicting the risk of prolonged pregnancy among nulliparous women.

METHODS

A retrospective cohort study was conducted between February 2022 and June 2024 at a regional tertiary maternity hospital. Transvaginal (TVS) and transabdominal sonography (TAS) were performed in low-risk nulliparous patients at 37 weeks of gestation. Patients were categorized into two groups based on delivery time: <41 weeks (term) and ≥41 weeks (late-term). Demographic, obstetric, and ultrasonographic parameters were compared between groups. Logistic regression was used to identify independent predictors of late-term delivery. Agreement between TVS and TAS measurements was assessed using Bland-Altman analysis. Statistical analyses were performed using SPSS software (version 27.0; IBM SPSS Inc., Chicago, IL, USA) and a p value < 0.05 was considered statistically significant.

RESULTS

A total of 179 patients were included in the study. Of these, 19 (10.6%) were classified as late-term group, while 160 (89.4%) were classified as term group. Maternal age and BMI were similar between groups. The median CL was higher in the late-term group by both TVS and TAS; however, only TVS-CL remained statistically significant (p = 0.032) in the late-term group. Bland-Altman analysis showed acceptable agreement between TAS and TVS measurements with a mean difference of 1.47 mm and 95% limits of agreement ranging from -6.8 to 9.8 mm. After adjusting for potential confounders, a longer TVS-CL was independently associated with an increased risk of late-term delivery (adjusted OR = 1.26; 95% CI 1.01-1.58). A positive correlation was observed between measured transvaginal CL at 37 weeks and gestational age at delivery.

CONCLUSION

A longer cervical length measured by transvaginal sonography at 37 weeks was independently associated with an increased risk of late-term delivery. Our findings demonstrate the potential value of standardized ultrasonographic assessment in identifying women at risk of prolonged pregnancy, which could help optimize perinatal outcomes.