Cervical elastography at 18 to 23 weeks to predict spontaneous preterm birth in individuals with a history of preterm birth

Abstract

Background: Individuals with a history of spontaneous preterm birth are at increased risk for recurrence in a subsequent pregnancy. Current methods used to predict those at highest risk are not precise. Cervical elastography is an investigational ultrasonographic technique that measures cervical tissue stiffness and may aid in identifying individuals at highest risk.

Objective: This study aimed to assess the association between previously described cervical elastography measures-obtained using a semiautomatic application (E-cervix)-and preterm birth <37 weeks' gestation in a high-risk cohort with a history of spontaneous preterm birth.

Study design: Individuals with a singleton pregnancy between 18+0 and 23+6 weeks of gestation with a history of spontaneous preterm birth <37 weeks were prospectively enrolled. Exclusion criteria included the presence of a current cerclage or any uterine anomaly. The primary exposures were the E-cervix quantitative parameters (internal os stiffness, external os stiffness, internal-to-external os stiffness ratio, hardness ratio, and elasticity contrast index), which were measured at the time of enrollment. Transvaginal cervical length was also measured as an exposure to compare the current standard of care and accepted cutpoint of 25 mm alongside the E-cervix parameters. The primary outcome was preterm birth <37 weeks. The intra- and interrater reliability intraclass correlation coefficient for each parameter was calculated using a mixed-effects model. The area under the curve was derived from receiver operating characteristic curves to evaluate the association of each parameter with the primary outcome, and the optimal cutpoints for each continuous parameter were identified. Multivariable logistic regression was performed for the parameters that were either significant on univariate analysis or had an area under the curve of ≥0.6, using the calculated cutpoint to create a binary exposure and adjusting for gestational age at the earliest prior preterm birth, number of prior preterm births, and progesterone use. A sensitivity analysis was performed excluding medically indicated preterm birth.

Results: Of the enrolled 245 individuals with a history of spontaneous preterm birth, 69 (28%) had preterm birth <37 weeks. Intrarater and interrater reliability were good for all parameters (intrarater: 0.60-0.74; interrater: 0.62-0.71). In univariate analysis, only the internal-to-external os stiffness ratio was significantly associated with increased risk of preterm birth compared with no preterm birth (0.97±0.23 vs 0.90±0.20; P=.01). Cervical length, internal os stiffness, external os stiffness, hardness ratio, and elasticity contrast index did not show significant associations. The area under the curve for external os stiffness was 0.6, indicating a good association, whereas the values for the remaining parameters were satisfactory (0.51-0.59). In multivariable logistic regression analysis, an internal-to-external os stiffness ratio ≥1.0 was associated with 2-fold higher odds of preterm birth <37 weeks (adjusted odds ratio, 2.48; confidence interval, 1.34-4.58), and an external os stiffness ≥30 (indicating lower tissue stiffness) was associated with 46% reduced odds of preterm birth <37 weeks (adjusted odds ratio, 0.54; confidence interval, 0.30-0.97). Cervical length <25 mm was not associated with preterm birth.

Conclusion: Elastography with E-cervix technology can be reliably assessed in a cohort of women with prior preterm birth. The parameter most useful for predicting preterm birth was an internal-to-external os stiffness ratio ≥1.0, whereas cervical length <25 mm was not predictive in our cohort.

Keywords: cervical length; elastography; preterm birth; spontaneous preterm birth; transvaginal ultrasound.

Figure 1

E-cervix parameter definitions and image diagram CL, cervical length.

Figure 2

Flow diagram of enrollment and preterm birth outcome