(1179) Utero-cervical angle in standing position improves prediction of spontaneous preterm birth: a multicenter cohort study

Objective: Measuring cervical length (CL) is a standard practice of stratifying the likelihood of preterm birth (PTB). Dynamic changes in the cervix can also be explored by placing the patient in the upright position, i.e. in the usual position of activity and measuring the shortening of the cervix and changes in the utero-cervical angle (UCA). The aim of this study is to determine whether dynamic measurement of CL and UCA improves prediction of PTB compared additionally to the CL measurement performed in a gynecological position.

Study Design: This is a prospective cohort study of women who had vaginal ultrasound exam for CL measurement at 4 institutions in Canada and Switzerland. The ultrasound exam was performed endovaginally in the supine position , then in the standing position with measurements taken at 1 minute, 3 minutes and during standing Valsalva (SV). UCA were measured after the exam on the images according to a standardized measurement procedure and the differences in UCA (DUCA) between the supine and standing positions were calculated.



Results: 253 participants were included, with a mean age at ultrasound of 27.4 weeks of gestation (WG), a median CL of 26 mm, and a funneling present in 29% of cases in the gynecological position. Among those women, 68 (26.8%) experienced PTB. LC mean was 28.5mm (standard deviation (SD) 10) at rest and 27.3mm (11.5) in SV in the term group, compared with 23.5mm (10.2) and 21.4mm (10) in the PB group respectively. The UCA mean was 113° (25) at rest and 115° (28) in SV in the term group compared with 88.6° (25) and 99° (27) in the PTB group respectively. From the ROC curves, we chose a threshold for UCA of 104° and 5° for DUCA (figure 1). Among participants with LC < 31mm, the use of UCA and DUCA significantly improved the prediction of PB but not the LC.

Conclusion: Using endovaginal screening to select a population at risk of PB (LC < 31mm), the use of UCA measurement and its variation between the supine and upright positions (DUCA) improves prediction of PB.