Quantification of cervical stiffness changes in single and twin pregnancies using the E-Cervix technique

Cervical length is a commonly used clinical indicator for evaluating preterm birth. However, some studies have shown that cervical length does not change in patients with cervical insufficiency.

This study aimed to use the transvaginal ultrasound E-Cervix to quantitatively evaluate the cervical stiffness in women with singleton and twin pregnancies to provide a reference for the clinical prediction of preterm birth.

We collected the cervical length, cervical hardness ratio, mean internal os strain, and mean external os strain using transvaginal ultrasonographic E-Cervix assessments in pregnant women undergoing routine examinations in the obstetrics department of our hospital from January 2020 to December 2020. We summarized the range of cervical elasticity parameters at different gestational ages and compared the cervical elasticity parameters between singleton and twin pregnancies and between preterm births and full-term births.

A total of 988 pregnant women were enrolled in this study, and after exclusion, 770 pregnant women were enlisted; the interrater and internal consistency for various elasticity parameters were favorable; and cervical elasticity changes in women at full term showed some particular patterns. The declines in cervical length and hardness ratio were commensurate with gestational age, whereas the internal os strain and external os strain rose with increasing gestational age. The cervical hardness ratio in women with twin pregnancies was lower than in women with singleton pregnancies at the same gestational age, although the internal os strain in women with twin pregnancies was higher than in women with singleton pregnancies at the same gestational age (P<.05). The cervical length of women with twin pregnancies was shorter than that of women with singleton pregnancies at the same gestational age when the gestational age was ≥28 weeks of gestation (all P<.05), and the hardness ratio was linearly correlated with gestational age (r=0.68 and r=0.71). The regression model for the cervical hardness ratio in women with singleton pregnancies was hardness ratio = -0.8764×gestational age+100.99, whereas the regression model for the cervical hardness ratio in women with twin pregnancies was hardness ratio = -1.3037×gestational age+103.03. When we compared cervical elasticity parameters between preterm and full-term births, we noted that the cervical hardness ratio in pregnant women who exhibited preterm births was lower regardless of whether they carried singleton or twin pregnancies (P=.000 and P=.000), although their internal os strain was higher (P=.023 and P=.000). We observed no significant difference when we compared the cervical length and external os strain of pregnant women manifesting preterm births vs women with full-term births (P=.216 and P=.345 vs P=.475 and P=.363).

When used for the quantification of cervical hardness, the E-Cervix cervical elasticity changes in pregnant women at full term showed some particular patterns. Cervical length and hardness ratio diminished as gestational age increased, whereas internal os strain and external os strain rose as gestational age increased; moreover, the degree of these changes was greater in women with twin pregnancies than in women with singleton pregnancies. Pregnant women experiencing preterm births exhibited a reduced cervical hardness ratio and augmented internal os strain relative to women experiencing full-term births.