Cervical elastography in predicting spontaneous preterm birth in singleton pregnancy with a short cervix receiving progesterone treatment at 18 to 24 weeks' gestation.

BACKGROUND: A short cervix in the second trimester is known to increase the risk of preterm birth, which can be reduced with the administration of vaginal progesterone. However, some studies have suggested that a significant number of cases still experience preterm birth despite progesterone treatment.

OBJECTIVE: This study was aimed to investigate the potential value of transvaginal cervical elasticity measured by E-Cervix as a predictor for spontaneous preterm birth (sPTB) in singleton pregnancies receiving progesterone treatment for a short cervix (CL ≤ 2.5 cm) diagnosed at 18 to 24 weeks' gestation.

STUDY DESIGN: This prospective study was conducted at a single center premature high-risk clinic from January 2020 to July 2022. Singleton pregnancies with a short cervix at 18 to 24 weeks' gestation were enrolled. Cervical elastography using E-Cervix was performed, and maternal and neonatal demographic characteristics, cervical length (CL), elasticity contrast index (ECI), cervical hardness ratio, mean internal os strain (IOS), and mean external os strain (EOS) were compared before and after progesterone treatment in sPTB and term birth groups. Multivariate logistic regression was used to analyze the association between elasticity parameters and spontaneous preterm birth. The screening performance of CL and optimal cervical elasticity parameters in predicting sPTB was evaluated using receiver-operating characteristic (ROC) curve analysis.

RESULTS: A total of 228 singleton pregnant women were included in the study, among which 26 (11.4%) had sPTB. There were no significant differences in maternal characteristics and gestational age at enrollment between women with and without sPTB. At the start of progesterone treatment, there were no significant differences in cervical elasticity parameters between the two groups. After two weeks of progesterone treatment, women who had sPTB showed significantly higher levels of ECI, IOS, EOS ( p  = 0.0108, 0.0001, 0.016), and lower hardness ratio ( p  = 0.011) compared to those who had a full-term birth. Cervical length did not show significant differences between the two groups, regardless of whether progesterone treatment was administered before or after. Among the post-treatment cervical elasticity parameters, IOS and EOS were associated with a 3.38-fold and 2.29-fold increase in the risk of sPTB before 37 weeks ( p  = 0.032, 0.047, respectively). The AUROC of the combined model including CL, IOS, and EOS (0.761, 95% CI0.589-0.833) was significantly higher than the AUROC of CL alone (0.618, 95% CI 0.359-0.876). At a fixed false-positive of 13%, the addition of IOS and EOS in the CL model increased sensitivity from 34.6% to 57.6%, PPV from 25.7% to 36.5%, and NPV from 91.1% to 94.1%.

CONCLUSION: When assessing the risk of sPTB in singleton pregnancies with a short cervix receiving progesterone therapy, relying solely on cervical length is insufficient. It is crucial to also evaluate cervical stiffness, particularly the strain of the internal and external os, using cervical elastography.