OBJECTIVE: The purpose of this study was to evaluate the agreement between and reproducibility of specific two-dimensional (2D) and three-dimensional (3D) ultrasound methods in assessing cervical volume in pregnant women in their second trimester.
MATERIALS AND METHODS: This was a prospective cross-sectional study of 48 asymptomatic pregnant women at 20–24 weeks of gestation. All cervical volumes were determined by transvaginal ultrasound, with a 2D method employing a geometric formula {π * [(anteroposterior diameter + transverse diameter) * ¼] * length}, where π = 3.14, and a 3D method employing a virtual organ computer-aided analysis. Intraobserver and interobserver reliability was analyzed by calculating the intraclass correlation coefficient (ICC).
RESULTS: The mean maternal age and timing of the ultrasound examination were 26 ± 6 years and 21 ± 1 weeks of gestation, respectively. The mean cervical volumes measured by the 2D and 3D ultrasound methods were 27.71 ± 9.27 cm³ and 35.21 ± 8.85 cm³, respectively. Cervical length and volume showed a positive correlation with both methods—r = 0.77 (p < 0.001) and r = 0.70 (p < 0.001), respectively. Intraobserver reliability was excellent for both methods, with ICCs of 0.92 and 0.93 for the 2D and 3D methods, respectively. Interobserver reliability was good (ICC: 0.81) for the 3D method, whereas it was poor (ICC: 0.37) for the 2D method. Reproducibility of the transverse diameter measurement was low, with an intraobserver ICC of 0.41 and an interobserver ICC of 0.48.
CONCLUSION: Cervical volume measurements obtained with 2D and 3D ultrasound methods seem to show satisfactory agreement and good intraobserver reliability. In our study sample, the 2D ultrasound method showed low interobserver reliability, whereas the 3D ultrasound method was more reliable, with good intraobserver and interobserver reliability.

Keywords: Pregnancy; Cervical length measurement; Cervix uteri/embryology; Pregnancy trimester, second; Ultrasonography, prenatal/methods; Reproducibility of results.