A novel ultrasound parameter help predicts mid-trimester cerclage failure-- -- News from SMFM 2017, Las Vegas.

UCA  acute and obtuse Courtesy Researchgate 

Increasingly wide utero cervical angle (UCA) after mid trimester cerclage operation signifies increase risk of preterm delivery.

Dr. Jordan Knight and his colleagues from Indiana University School of Medicine, Indianapolis, IN presented a pilot study, utilizing UCA in predicting the failure of mid-trimester transvaginal cerclage operations. [1]

UCA is defined as the triangular area between the lower uterine segment and cervical canal measured by Transvaginal Ultrasonography (TVUS).

Researchers are exploring the possibilities of using a novel ultrasound parameter, the anterior utero cervical angle (UCA) as a predictor of Spontaneous Preterm Birth along with Cervical length (CL). Previously this angle has been used as one of the parameter for successful induction of labor.

The pathophysiological   principle behind this is based on physics and trigonometry. Pregnant uterus exerts pressure on cervix and depending on the angle of inclination, the cervix is either shut if the angle is acute or opened wide if the angle is obtuse.

The current retrospective study collected data on 142 women who underwent transvaginal cerclage between 2010-2015. UCL was measured thrice in same patient: prior, one week after cerclage placement and prior to delivery by TVUS.

Delivery before 36 weeks was labelled as cerclage failure.

After Univariate regression, it was seen that CL and UCL was strongly associated with gestational age at birth.

UCL angle of 108 degree prior to 34 weeks was a better predictor of preterm delivery than CL = 25 mm. Before28 weeks the UCL angle of 112 degree had 100 sensitivity as compared to 29% that of CL.

Patients with UCA angle> 108 degree had 35 times higher odds of spontaneous preterm birth (PTB) before 34 weeks while the UCL > 112 degree conferred 42 times higher odds of delivering before 28 weeks.

The corresponding odds of delivery if cervical length CL<25mm are 4.7 and OR 6.0 prior to 34 and 28 weeks respectively.

The study cohort had 38% cerclage failure rate and delivered at mean gestational age of 29 +/- 5.2 weeks compared to those who delivered at 37.9 +/- 2.8 weeks (p<0.001).

A study presented at the 36th Annual Pregnancy Meeting concluded that “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.”[2]

The authors concluded that increasing obtuse UCA signify increase chances of cerclage failure and give the obstetrician valuable time to make arrangements for delivery at tertiary center.

UCA performed better than CL as a screening parameter for predicting preterm births (PTB) because of increased sensitivity and NPV.

In fact, a combination of UCA and CL synergistically can be best predictor of PTB in cerclage patients.

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[1] http://www.ajog.org/article/S0002-9378(16)31012-2/fulltext

[2] http://www.ajog.org/article/S0002-9378(16)00525-1/abstract