Uterocervical angle a sensitive predictor of preterm birth

1. Uterocervical angle (UCA) greater than 95° and 105° were associated with spontaneous preterm birth at <37 weeks and <34 weeks respectively.

2. UCA was more sensitive than cervical length (CL) in predicting preterm birth.

Evidence Rating Level: 2 (Good)           

Study Rundown: Preterm birth, defined as birth before 37 weeks gestation, complicates 10% of births worldwide and is associated with considerable infant morbidity and mortality. Two well-established risk factors for preterm birth are prior preterm birth and short CL on ultrasound. The pathogenesis of preterm birth is thought to include early activation of the maternal or fetal hypothalamic-pituitary-adrenal axis, exaggerated inflammatory response, abruption, and pathological uterine distention. The shared common pathway in these processes is hypothesized to be cervical shortening. While CL screening is not routinely recommended for all pregnant women, it may expedite early intervention in those at greater risk. Prior work has suggested that a wider UCA on transvaginal ultrasound (TVUS) results in an anatomical arrangement of pelvic organs that places greater force on the internal os. However, the association between UCA and preterm birth has not been well studied. In the present work, authors evaluated this relationship and found that an obtuse UCA was associated with spontaneous preterm birth (sPTB).

Major findings of this work include a higher sensitivity but lower specificity for detecting preterm birth using UCA compared to CL. Strengths of the study included prospectively collected ultrasound images. Limitations were retrospective design and use of ultrasound images not obtained for the purpose of measuring UCA. Prospective investigation of the relationship between UCA and preterm delivery is merited. Additionally, other parameters, such as interrater variability in UCA measurement and use in combination with CL, are needed to better characterize its use as a screening tool.

Click to read the study in AJOG

Relevant Reading: Anterior cervical angle as a new biophysical ultrasound marker for prediction of spontaneous preterm birth

In-Depth [retrospective cohort]: This study evaluated the ability of UCA as measured on TVUS to predict sPTB in 972 women who underwent a TVUS between 16 and 0/7 and 23 and 6/7 weeks gestation. UCA was defined as the triangular area between the lower uterine segment and cervical canal. The primary outcome of interest was sPTB <34 and <37 weeks as predicted by UCA. The secondary outcome was sPTB <34 and <37 weeks as predicted by CL ≤25mm.

UCA >95° had 80% sensitivity, 53% specificity, 14% positive predictive value (PPV) and 95% negative predictive value (NPV) for birth at <37 weeks. Comparatively, CL ≤25mm had 15% sensitivity, 98% specificity, 46% PPV, and 92% NPV for birth at <37 weeks. For birth at <34 weeks, UCA >105° had 81% sensitivity, 65% specificity, 10% PPV and 99% NPV. In comparison, CL had 19% sensitivity, 98% specificity, 29% PPV and 96% NPV.

Image: PD

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