Reference ranges for cervical length by transvaginal scan in singleton pregnancies

Abstract

Objective. The aim was to construct a chart for cervical length measured by transvaginal ultrasound.

Research design and methods. Singleton pregnant women underwent a transvaginal scan to measure the cervical length (CxL) from 20 to 34 weeks. Exclusion criteria were preterm delivery, preterm rupture of membranes, multiple pregnancies, cerclage, and those who have taken vaginal progesterone. For statistical evaluation, we used regression analysis and calculation of 5th, 50th, and 95th centiles was performed.

Results. In the 1061 women with follow up, there were 94 (8.8%) spontaneous and 27 (2.5%) iatrogenic preterm delivery before 37 weeks. The CxL decreased with gestational age (r² = 0.0799). The coefficient for the interpolated median is y = 37.754 − 0.0148 × (GA)² + 0.2556 × (GA) (r² = 0.7247); for the 5th centile is y = 5.9171 − 0.0467 × (GA)² + 1.7059 × (GA) (r² = 0.6502); and for the 95th centile is y = 114.72 + 0.0758 × (GA)² − 4.6706 × (GA) (r² = 0.7783).

Conclusion. CxL shortened throughout the pregnancy. The chart present 5th, 50th, and 95th centile, respectively, at 23 weeks of 20 mm, 36 mm, and 47 mm; at 28 weeks of 17 mm, 33 mm, and 43 mm; and at 34 weeks of 10 mm, 29 mm, and 43 mm.

Keywords:

• Cervical length
• transvaginal scan
• normal ranges
• preterm delivery

Declaration of interest: The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the paper.