Cervical Characterization with Tactile-Ultrasound Probe

Abstract

Background: Premature cervical softening and shortening may be considered an early mechanical failure that predisposes to preterm birth. Preliminary clinical studies demonstrate that cervical elastography may be able to quantify this phenomenon and predict spontaneous preterm delivery.

Objective: To explore a new approach for cervix elasticity and length measurements with tactile-ultrasound probe.

Methods: Cervix probe has tactile array and ultrasound transducer designed to apply controllable load to cervix and acquire stress-strain data for calculation of cervical elasticity (Young's modulus) and cervical length for four cervix sectors. Average values, standard deviations, intraclass correlation coefficients and the 95% limits of agreement (Bland-Altman plots) were estimated.

Results: Ten non-pregnant and ten pregnant women were examined with the probe. The study with non-pregnant women demonstrated a reliable acquisition of the tactile signals. The ultrasound signals had a prolonged appearance; identification of the internal os of the cervix in these signals was not reliable. The study with pregnant women with the gestational age of 25.4 ± 2.3 weeks demonstrated reliable data acquisition with real-time visualization of the ultrasound signals. Average values for cervical elasticity and standard deviations of 19.7 ± 15.4 kPa and length of 30.7 ± 6.6 mm were calculated based on two measurements per 4 sectors. Measurement repeatability calculated as intraclass correlation coefficients between two measurements at the same cervix sector on pregnant women was found to be 0.97 for cervical elasticity and 0.93 for the cervical length. The 95% limits of agreement of 1) cervical elasticity were from -22.4% to +14.9%, and 2) cervical length from -13.3% to +16.5%.

Conclusions: This study demonstrated clinically acceptable measurement performance and reproducibility. The availability of stress-strain data allowed the computation of cervical elasticity and length. This approach has the potential to provide cervical markers to predict spontaneous preterm delivery.

Keywords: Cervical Elasticity; Cervical Length; Elastography; Premature Cervical Softening; Spontaneous Preterm Delivery; Tactile; Ultrasound.

Figure 1.

Cervical probe. (A) General view of the Cervix Monitor probe; (B) Probe tip with tactile and ultrasound transducers; (C) Probe positioning at cervical measurement.

Figure 2.

Measurement approach. (A) Ultrasound signals reflected from internal cervical os during cervix deformation by the probe; (B) Stress (pressure)-strain (compression) data recorded for 32 y.o. women at 25 week pregnancy.

Figure 3.

Cervical elasticity and length for 10 pregnant women measured by Cervix Monitor. Cervical Map with four sectors shows measurement results for subject number 10.

Figure 4.

Relationship for two measurements. Intraclass correlation coefficients (ICC) for two measurements of cervical elasticity (A) and length (B) by the same operator.

Figure 5.

Scatter plots of difference between two measurements. Bland-Altman scatter plot of the percentage difference between two measurements of cervical elasticity (A) and length (B) by the same operator. The solid lines represent the proportionate mean difference; the dashed lines represent the 95% limits of agreement.