Cervical Stiffness in Mid-Pregnancy: A Predictive Tool Using a Novel Aspiration Device for Spontaneous Preterm Birth Risk Assessment

Abstract Background Preterm birth is a major prenatal care problem. Predicting who will deliver prematurely is particularly challenging in women who do not present known risk factors. Abnormal cervical softening can contribute to a higher risk for spontaneous preterm delivery; a clinically deployable technique to accurately measure cervical stiffness could improve identification of women at risk. Objective This study aimed at evaluating differences in cervical stiffness measured mid-pregnancy with the aspiration-based Pregnolia System between largely unselected pregnant women who ultimately delivered at term and the ones who had a spontaneous preterm birth; and to evaluate the performance of stiffness in predicting spontaneous preterm birth. Study Design This was a cross-sectional, prospective, cohort study of pregnant women presenting at their mid pregnancy consultation (gestational age 18 0/7 – 22 0/7 weeks) conducted at 13 centers. Cervical stiffness, assessed as Cervical Stiffness Index (CSI), was measured with an aspiration-based device placed on the anterior lip of the cervix during a speculum examination. Stiffness was also determined through the maximum cervical compressibility ratio (Cervical Consistency Index, CCI) and cervical length was measured transvaginally. Pain or discomfort scoring (from 0 – no pain to 10 – maximum possible pain), and delivery information were also recorded. Results Data from 1002 women were analyzed, of which 990 were singleton pregnancies. Preterm birth rate (5.2%) in the whole dataset was considerably lower than expected, with 25 spontaneous among a total of 52 preterm births. A significant difference in mean CSI between singleton women delivering at term (median=71 mbar, IQR=(51,97), n=948) and women delivering spontaneously prematurely before 37 weeks (65 mbar (42,70), n=19) was found (p=0.039). Instead, the difference in cervical length and CCI was not significant. Women who had no prior vaginal delivery had a cervix on average 15% stiffer (75 mbar (55,103), n=590) than those with a previous vaginal delivery (64 mbar (45, 85), n=358) (p<0.001). In the sub-population without history of vaginal delivery, the difference in CSI between women with a term birth (75 mbar (55,103)) and women with a spontaneous preterm birth (59 mbar (42,70), n=15) was more significant (p=0.007). Mean discomfort score for CSI assessment was 0.51±1.32. Conclusion Women with singleton pregnancies delivering spontaneously preterm had a significantly lower cervical stiffness than those delivering at term. This difference is even more significant in a sub-population without history of vaginal delivery. Women with a term birth and no history of vaginal delivery had a significantly stiffer cervix than women with a history of vaginal delivery, suggesting that mechanical properties of the cervix are softened by prior vaginal birth. Quantitative measurement of cervical stiffness with the aspiration-based Pregnolia System proved robust for objective measurement of cervical softness during pregnancy, with a very low discomfort score.