Uterocervical angle: a novel ultrasound screening tool to predict spontaneous preterm birth

Abstract

Background: Mechanical alteration of the cervical angle has been proposed to reduce spontaneous preterm birth. Performance of the uterocervical angle as measured by ultrasound for predicting spontaneous preterm birth is poorly understood.

Objective: We sought to determine whether a novel ultrasonographic marker, uterocervical angle, correlates with risk of spontaneous preterm birth in a general population.

Study design: We conducted a retrospective cohort study from May 2014 through May 2015 of singleton gestations between 16 0/7-23 6/7 weeks undergoing transvaginal ultrasound for cervical length screening. Images were remeasured for uterocervical angle between the lower uterine segment and the cervical canal. Primary outcome was prediction of spontaneous preterm birth <34 weeks and <37 weeks by uterocervical angle and secondary outcome evaluated cervical length and spontaneous preterm birth.

Results: A total of 972 women were studied. The rate of spontaneous preterm birth in this cohort was 9.6% for delivery <37 weeks and 4.5% for <34 weeks. Uterocervical angle of ≥95 degrees was significantly associated with spontaneous preterm birth <37 weeks with sensitivity of 80% (P < .001; confidence interval, 0.70-0.81; negative predictive value, 95%). Uterocervical angle of ≥105 degrees predicted spontaneous preterm birth <34 weeks with sensitivity of 81% (P < .001; confidence interval, 0.72-0.86; negative predictive value, 99%). Cervical length ≤25 mm significantly predicted spontaneous preterm birth <37 weeks (P < .001; sensitivity, 62%; negative predictive value, 95%) and <34 weeks (P < .001; sensitivity, 63%; negative predictive value, 97%). Regression analysis revealed a significant association of maternal age, nulliparity, race, and obesity at conception with spontaneous preterm birth and uterocervical angle. There was no correlation identified between history of dilation and curettage, abnormal Pap smear results, excisional cervical procedures, smoking, or obesity at delivery on spontaneous preterm birth and uterocervical angle.

Conclusion: A wide uterocervical angle ≥95 and ≥105 degrees detected during the second trimester was associated with an increased risk for spontaneous preterm birth <37 and <34 weeks, respectively. Uterocervical angle performed better than cervical length in this cohort. Our data indicate that uterocervical angle is a useful, novel transvaginal ultrasonographic marker that may be used as a screening tool for spontaneous preterm birth.

Keywords: cervical length; preterm birth; transvaginal ultrasound; uterocervical angle.