Assessment of cervical softening and the prediction of preterm birth (STIPP study); a prospective cohort study

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Oudijk, Benjamin Gravesteijn, Marjon de Boer, and 2 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-7063902/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract Preterm birth(PTB) is a global health problem and selecting pregnancies at risk is still a challenge. This study evaluates characteristics of cervical softening as a novel biomarker to predict birth in patients presenting with symptoms of threatened PTB. This is a single center cohort study. Pregnancies between 24 +0 and 34 +0 weeks presenting with symptoms of threatened PTB and intact membranes were included. The cervical stiffness index (CSI) was measured with the Pregnolia® System, providing a quantitative measure of tissue consistency. Lower CSI indicates a softer cervix. Primary outcome was delivery within seven days. We included 163 patients between August 2022 and October 2024 . The primary outcome occurred in 6.5% patients (n=10). Cervical stiffness index was significantly lower in patients delivering within seven days (29.0 mbar [IQR: 24.3-51.8] vs. 69.0 mbar [51.0-90.8]) and adequately discriminated between patients with and without outcome (AUC 0.77 (0.55-0.99)). No correlation between cervical length and CSI was found (ρ=0.12). Patients with a short and soft cervix are most at risk for birth within seven days. A soft cervix, as quantified by a low CSI, in pregnancies with symptoms of threatened PTB is associated with an increased risk of birth within seven days. CSI could be used to distinguish patients with a short cervix who are at risk for preterm birth and could improve risk assessment. Health sciences/Medical research/Outcomes research Health sciences/Risk factors Figures Figure 1 Figure 2 Figure 3 Introduction Spontaneous preterm birth (sPTB) is a global problem and is the leading cause of perinatal and neonatal morbidity and mortality. 1, 2 Neonates who survive PTB are at risk for physical and developmental sequalae, representing significant burden on healthcare systems and society. 3, 4 Pregnant patients frequently experience symptoms suggestive of threatened PTB. However, identification of patients at high risk for birth within seven days is challenging. Patients who are likely to deliver, require treatment with antenatal corticosteroids to improve perinatal outcomes and need to be admitted to a center with NICU facilities depending on gestational age. 5 Primary method for predicting the risk of birth within seven days in cases of threatened preterm birth is the measurement of cervical length using a transvaginal ultrasound. Other biomarkers, such as fetal fibronectin (fFN), phosphorylated insulin-like growth factor binding protein-1 (phIGFBP-1) or placental alpha microglobulin-1 (PAMG-1) can be used to as an addition to cervical length measurement. 6-8 Current identification methods are characterized by a high negative predictive value (NPV). However, this results in low positive predictive value (PPV) leading to false positive tests and unnecessary admissions. 9-11 By improving this risk assessment, we can avoid overtreatment, reduce healthcare costs and alleviate stress for pregnant patients. Thus, the search continues to more accurate identification of pregnancies at risk for preterm birth among those presenting with symptoms of threatened PTB. Although sPTB is a multifactorial problem with several pathophysiological pathways, clinically these all result in the final common pathway to birth: cervical softening, shortening and dilation. 12 These processes follow different time courses and progress in parallel rather than sequentially, suggesting that cervical softening and shortening may offer distinct or complementary insights. 13 Cervical consistency during pregnancy, is recognized as a key factor influencing cervical function. 12-16 Parra-Saavedra et al. found that cervical consistency, measured by ultrasound, softens and thus decreases with gestational age. 15 The cervical consistency was significantly lower in patients with sPTB. Other techniques, such as strain elastography and shear wave elastography, show similar trends when assessing cervical consistency. 17 However, technical and safety challenges, including operator-dependent variability, affect their reliability and standardization. 18, 19 Recently, a new method was developed to measure cervical consistency during pregnancy. This technique is based on aspiration to assess tissue elasticity and expressed as cervical stiffness index (CSI). A previous study has demonstrated that this technique provides a safe and more consistent approach than physical examinations. 20 Therefore, CSI measurements could potentially be a novel marker to predict sPTB and contribute to better identification of patients with an increased risk of sPTB. The aim of this study is to evaluate CSI to predict the risk of birth in patients presenting with symptoms of threatened PTB. Results Between August 2022 and October 2024, 372 patients were screened for eligibility, of which 309 met the inclusion criteria. Finally, 163 patients (52.8%) participated the study (Figure 1). Median gestational age was 29.6 weeks [IQR 27.2 to 31.6] at enrollment. Eighty-four (51.5%) were nulliparous and 143 (87.7%) were singletons. Median cervical length was 25.0 mm [IQR 18.0 to 32.9] (Table 1). In eight patients (4.9%), CSI measurements were unsuccessful. Two resulted from difficulties to visualize the cervix, while six were due to an inability to establish a vacuum. One patient was lost to follow-up, leaving 154 patients for further analysis. When investigating three consecutive CSI measurements, discrimination decreased with the second and third measurements (Table 2). Hence, first measurement (CSI-1) was most representative, all subsequent references to CSI in this section refer to CSI-1. The primary outcome occurred in 10 patients (6.5%) and CSI was significantly lower in patients delivering within seven days (Table 2; 29.0 mbar [24.3-51.8] vs. 69.0 mbar [51.0-90.8]). Discrimination for this outcome was adequate (AUC 0.77 [95% CI; 0.55-0.99]). For the secondary outcomes, lower CSI measurements were associated with higher probabilities of birth within seven days, 14 days and sPTB before 32 weeks. Discrimination was lower for sPTB before 34 and 37 weeks (Table 2 and Figure 2). Outcomes for birth within 48 hours and before 28 weeks occurred in only six and four patients, respectively; therefore, analyses were not performed due to low numbers. Patients with a history of cervical surgery had higher CSI values (104.0 mbar [IQR: 83.0-117.5] versus 64.0 mbar [48.0-88.3]). Patients with cerclage placement, nulliparous and singletons have slightly higher CSI measurements (Table 3). Minimal correlation was observed between cervical length values and CSI (ρ=0.12 95% CI -0.04 – 0.28), suggesting that CSI could add new value to prediction of sPTB (Appendix). Exploratory analysis show a group of patients with a short cervix and high CSI value did not deliver within seven days. Contrary, most sPTB occurred in the lower left quadrant indicating that patients with short a cervical length in and low CSI are at risk for PTB (Figure 3). Safety and patient experience No adverse events or complications were reported. Fifty-four out of 149 patients (32.7%) reported the procedure as uncomfortable but not painful. All patients attributed this discomfort to use of the speculum, rather than the measurement itself. Discussion A soft cervix as quantified by a low CSI is associated with a higher risk of birth within seven days in patients with symptoms suggestive of threatened PTB. No significant correlation was found between CSI and cervical length measurement, therefore, CSI could provide new information to predict preterm birth. When combined with cervical length, CSI can potentially rule out patients at risk for preterm birth with a short cervix, thereby improving risk assessment. Measurement of CSI did not report adverse events or complications. Additionally, patients' experience reveals no discomfort attributed to the CSI measurement. However, one-third of the patients report discomfort due to the use of the speculum. A study from Badir et al. 29 demonstrated that cervical stiffness decreases throughout normal pregnancy and has an important role in the onset of labor. Their findings suggest that early and progressive decrease in cervical stiffness is associated with a higher risk of sPTB. Similarly, Stone et al. 16 studied asymptomatic patients with a history of cervical insufficiency. They found that patients undergoing ultrasound-indicated cerclage had a significantly lower CSI and thus stated measurement of cervical consistency can be a promising technique for assessment of patients at risk for cervical dysfunction. Our study adds to these findings that lower CSI in symptomatic patients is significantly associated with higher risk of birth within seven days. This shows that cervical softening plays a crucial role in giving birth. These findings are in line with other techniques, such as strain elastography and shear wave elastography, finding cervical softening to be a risk factor for preterm birth. These techniques are promising, yet currently limited by factors such as operator dependence, standardization challenges, and accessibility in clinical practice. 17 CSI measurements use a different approach, using direct mechanical assessment of cervical softening, offering a objective, easily performed measurement of cervical softening. Another important finding in line with current literature is that CSI is affected by cervical surgery. We found higher CSI values in patients with a history of cervical surgery, suggesting that scar tissue can affect CSI. This has also been described by Stone et al. 16 , where they found high CSI in patients with history of cervical surgery. This highlights the need caution when interpreting the CSI measurement in this population, as well as the importance of further research to better understand its implications. Use of CSI in prediction of birth in patients with threatened PTB appears promising. The timeline of biomechanical changes, as reflected by CSI measurements, differs from that of cervical length, indicating that these methods may offer distinct or complementary insights. Therefore, by incorporating CSI measurements into risk assessment it could enhance targeted medical interventions. Ultimately this may lead to reduction of overtreatment and unnecessary hospitalization. Further validation in larger populations is necessary to confirm these findings. This will improve generalizability and reliability of CSI across different demographic and clinical settings. Next step should be to validate prognostic value and evaluate its incremental value over of with other clinical variables such cervical length and biomarkers (fFN, phIGFBP-1 or PAMG-1). Ultimately it should be (cost-) effective to adjust current diagnostic algorithms. 30 In future research, we suggest using the first CSI measurement, due to its highest discrimination, with a decrease in predictive capability seen in CSI-2 and CSI-3. Clinically, CSI-1 is also the preferred choice since it represents tissue characteristics before any deformation occurs. We discourage the use of averages of the three consecutive measurements: this combines more predictive and less predictive measurements, potentially resulting in a less predictive overall measure. Another focus is applicability of CSI measurements across various etiologies of sPTB. 31 As previously shown by Stone et al. 16 , early cervical softening is a significant predictor in cases of cervical insufficiency. However, it could be hypothesized that CSI measurements have limited predictive value in twin pregnancies, where the mechanism of sPTB is more closely associated with uterine overdistension. 31 On the other hand, it could also be argued that regardless of the underlying cause, sPTB starts with early cervical remodeling (softening, shortening and dilatation), suggesting that the measurement may hold predictive value irrespective of the specific etiology. Consequently, it is essential to include a larger patient cohort to enable these subgroup analyses and assess the predictive value of the CSI within these diverse groups. A strength of this study is its design that includes predefined outcome measures and a registered protocol. The first stage has demonstrated that CSI provides predictive information regarding the risk of sPTB, offering new insights beyond cervical length. Also, this design ensures minimal interference with daily practice, making the study easier for clinicians to execute. Another strength is the use of birth within seven days as the primary outcome, given its direct impact on clinical decision-making. Current methods to identify patients at high risk for birth within seven days often result in the admission and treatment of the majority of those classified as high-risk, who ultimately do not deliver. By focusing on this outcome, improvement of identification could reduce overtreatment. A limitation was the prevalence of sPTB within seven days that was lower than expected (6.5% versus 12.0%). One possible explanation is the fact that clinicians may be overly prone to including patients, potentially leading to the inclusion of individuals who do not actually exhibit true symptoms of threatened PTB. This may be reinforced by the inclusion criteria being primarily based on symptoms rather than objective measurements, such as cervical length or contractions on the cardiotocography. Consequently, the role of clinical judgment by healthcare professionals is overseen and the threshold for inclusion is low. Moreover, patients with severe symptoms, might avoid additional diagnostic procedures, leading to their decision to decline participation. Consistent with the fact that speculum use is widely recognized as uncomfortable, and in line with the limitations described by Stone et al. 16 , the requirement of speculum examination for the measurement, was identified as the primary reason for refusal. This factor may be further amplified if a patient with true, severe symptoms are at higher risk, yet choose not to participate. In future, CSI measurement might enhance targeted patient care to such an extent that patients recognize their individual benefits, making them more willing to undergo the possible discomfort of a speculum examination. Lastly, the CSI measurement is limited to investigating a relatively small amount of cervical tissue on the ectocervix. No information is provided about mechanical properties of the internal os, where cervical shortening starts. However, a previous study 14 investigating the same device, concluded that the observed time course of the decrease of CSI measured on the ectocervix, parallels the compliance changes in the entire cervix as described by Parra-Saavedra et al. 15 Conclusion A soft cervix, as quantified by a low CSI, in patients presenting with symptoms of threatened PTB is associated with an increased risk of birth within seven days. The observation of no significant correlation between cervical length and CSI suggests that CSI provides new information and can potentially improve risk assessment for sPTB. Measurements of CSI could identify a group of patients with a short but stiff cervix who do not deliver within seven days. Therefore, the use of CSI measurement can potentially help in reducing unnecessary admission and overtreatment. Important next steps include determining its incremental value over cervical length and integrating it into a prediction model to better assess birth in patients facing threatened PTB. Methods Study design and participants This study is an investigator-initiated, single-center cohort study conducted at the Amsterdam University Medical Center in the Netherlands, a tertiary referral center. Recruitment started on 18 th August 2022. The study was approved by the Medical Ethics Committee of Amsterdam UMC (METC2022.0226) and the protocol was prospectively registered at ClinicalTrials.gov (NCT05477381) and published. 21 All pregnant patients presenting with symptoms of threatened PTB, such as regular painful contractions, abdominal or back pain, vaginal bleeding, with a gestational age between 24 and 34 weeks and intact membranes, were eligible for the study. Exclusion criteria were sings of intrauterine infection, confirmed fetal abnormalities, vasa or placenta previa and other obstetric indications requiring immediate delivery like advanced labor, cord prolapse, placental abruption, or fetal distress. Verbal and written informed consent were obtained from patients prior to the entry of the study. Methods All patients included received standard care as outlined by the Dutch Society for Obstetrics and Gynecology guideline on threatened PTB. 22 Standard care included cardiotocography to monitor contractions and fetal well-being, a midstream urine sample to rule out urinary tract infection, a transvaginal ultrasound to measure cervical length and a speculum exam for fFN testing. Transvaginal cervical length was measured according to the criteria proposed by Society for Maternal and Fetal medicine (SMFM) 23 and International Society of Ultrasound in Obstetrics and Gynecology (ISUOG). 24 Patients were classified as high risk for birth within seven days if their cervical length was <15mm. Those with cervical lengths of 15–30mm required an additional positive fFN test. Patients with a cervical length greater than 30 mm, as well as those with a cervical length of 15–30 mm and a negative fFN test, were classified as low risk. 9, 25 High risk patients were admitted and administered antenatal corticosteroids. Tocolysis and magnesiumsulphate were advised if the gestational age was under 30 weeks. 26 In addition to this standard care, all patients underwent CSI measurements and completed a questionnaire. Midway through patient recruitment, the fFN became unavailable. 27 This led to an adjustment in standard care for patients with a cervical length between 15-30 mm. In these patients, cervical length was repeated after two hours. If the subsequent measurement was shorter, patients were classified as high risk. Conversely, if the measurement remained the same or increased, it was classified as low risk. Cervical stiffness index measurement Cervical stiffness index was measured using the Pregnolia® System, which includes a control unit and a disposable, sterile probe. The control unit with integrated vacuum pump is connected to the probe with a cable. To measure CSI, the cervix was visualized with a speculum and the probe was placed on the anterior lip of the cervix. This region of interest is used in accordance with the instructions of the system since this point is the most consistently accessible throughout pregnancy, thereby improving reproducibility. The control unit generated a vacuum, pulling cervical tissue 4 mm into the probe tip. The outcome was the negative pressure in millibar (mbar) needed to deform the tissue. A higher pressure indicates stiffer tissue, and lower pressure indicates softer tissue. Cervical stiffness index was assessed with three consecutive measurements (CSI-1, CSI-2 and CSI-3, respectively) at the same location without removing the probe. When only one or two measurements were available, they were included in analysis based on these measurements. If CSI-1 was missing, CSI-2 and CSI-3 were shifted forward, following a last-carried-forward approach. If all measurements were unsuccessful patients were excluded from the final analyses. A selection of clinical staff was trained to perform the CSI measurements, to cover 24 hour availability. Treating physicians and patients were blinded to the measurement results. Patient experience We also assessed the patient’s experience, specifically evaluating the acceptability and tolerability of the procedure via a questionnaire. Outcome measures Primary outcome was birth within seven days after enrollment. Secondary outcomes were birth within 14 days, or sPTB before 28, 32, 34 and 37 weeks. Also, latency time defined as time between inclusion and birth, birth within 48 hours and premature prelabor rupture of membranes (PPROM) were evaluated. Outcome measures were evaluated only when at least 10 events for a given outcome had occurred. Safety was assessed by registering potential complications related to the procedure, including PPROM during or immediately after measurement, significant blood loss and intrauterine infection within seven days. Sample size This study was conducted with a dynamical sample size. To investigate the primary objective for the first step, evaluating CSI as a single predictor for birth within seven days, a sample size of 163 patients was required. 21 To investigate secondary objectives, such as the incremental value of CSI to cervical length, patient recruitment will continue. Contemporary sample size calculations for developing prediction models as described by Riley et al was used. 28 Parameters used for calculation included (1) expected prevalence of the primary outcome, (2) expected amount of explained variance by the prediction model and (3) number of predictors (input variables). For this study, prevalence of birth within seven days (0.12 = 12%) and expected R 2 explained by the new model (0.45) were derived from the APOSTEL I study 9 , as this study had a comparable population. Statistical analysis Baseline characteristics are calculated using descriptive statistics. Continuous variables are reported as mean with standard deviation (SD) or median with interquartile ranges (IQR). Categorical variables will be reported as proportions. Characteristics of CSI measurement were explored by comparing distributions of measures across patient characteristics that might influence cervical consistency (cerclage, nulliparity, history of cervical surgery, progesterone). To evaluate predictive ability of CSI and to select the most appropriate CSI measurement for analysis, we first compared distributions of the three CSI measurements among patients with and without outcomes of interest. Next, we fitted logistic regression models for primary and secondary outcomes, with CSI as independent variable. Area under receiver-operator-characteristic (ROC) curve (c-statistic) was calculated. Mean, 2.5 th percentile, and 97.5 th percentile were calculated and reported as 95% confidence interval. We selected the most relevant CSI measurement based on clinical insight together with the highest area under the ROC curve (AUC). The expected effect of the most relevant CSI measurement on our evaluated outcomes was displayed by calculating expected probability of the outcome for the range of CSI values. This was done by fitting logistic regression models with the outcomes as dependent and CSI as independent variable. We assumed a linear effect on the log-odds scale, because we did not have enough events to relax this assumption. Finally, we explored the potential incremental value of CSI over cervical length for the primary outcome. However, since the sample size of this study was powered for investigating CSI as a single predictor only, the events in the current dataset were too low for multiple regression. Therefore, visual analysis was performed with scatterplots. The co-distribution of CSI measures and cervical length were displayed for patients with and without the primary outcome. Analyses were performed using R (A language and environment for statistical computing. R Foundation for Statistical Computing, Vienna, Austria), version 4.2.1. Declarations Declaration of interest: None to declare Funding: This study was financially and in kind supported by Pregnolia AG. They also provided the system and the probes. The funders had no role in the study design, conduction of the study, collection, management, analysis and interpretation of the data. Also, the funder had no role in preparation, reviewing or approval of the manuscript. Tweetable statement: The cervix is softer in patients with threatened preterm birth who ultimately deliver within seven days. Acknowledgements: We would like thanks to R. van Eekelen for his assistance in determining the appropriate statistical methods to use for the execution of this study. Author contribution SB: conceptualization, data curation, formal analysis, investigation, methodology, project administration, resources, software, validation, visualization, writing – original draft MO: conceptualization, supervision, writing – review & editing BG: formal analysis, investigation, methodology, writing – review & editing MdB: conceptualization, writing – review & editing EP: conceptualization, writing – review & editing FH conceptualization, data curation, methodology, supervision, writing – review & editing. References Blencowe H, Cousens S, Oestergaard MZ, et al. 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Eur J Obstet Gynecol Reprod Biol X 2024;24:100343. NHS England. Discontinuation of Hologic fetal fibronectin testing. 2024. https://www.england.nhs.uk/long-read/discontinuation-of-hologic-fetal-fibronectin-testing/ (accessed October 23, 2024). Riley RD, Ensor J, Snell KIE, et al. Calculating the sample size required for developing a clinical prediction model. BMJ 2020;368:m441. Badir S, Mazza E, Zimmermann R, Bajka M. Cervical softening occurs early in pregnancy: characterization of cervical stiffness in 100 healthy women using the aspiration technique. Prenat Diagn 2013;33:737-41. Hlatky MA, Greenland P, Arnett DK, et al. Criteria for evaluation of novel markers of cardiovascular risk: a scientific statement from the American Heart Association. Circulation 2009;119:2408-16. Romero R, Dey SK, Fisher SJ. Preterm labor: one syndrome, many causes. Science 2014;345:760-5. Tables Tables 1 to 3 are available in the Supplementary Files section. Additional Declarations There is NO Competing Interest. Supplementary Files AppendixfigueS1.pdf Associations between cervical length, cervical stiffness index (CSI), and preterm birth within 7 days Tables.docx Cite Share Download PDF Status: Posted Version 1 posted You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-7063902","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Article","associatedPublications":[],"authors":[{"id":483988972,"identity":"96ab705d-2e9d-4160-95f1-ea91b6a60627","order_by":0,"name":"Sofie Breuking","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAABEUlEQVRIiWNgGAWjYFACHgZmECUBIj9AxSSgNOMBQloYZ4D5CC0M+LUAMTMPMVrkG3gPMBfusUmc2c57+LVNzTZ7e/behzd+5hyO5gdKYdNicIAvgXnGs7TE2cx8adY5x24n9vAcN7bs3XY4dwZQCqsWBh4DZp4DhxPnMfOYGeew3U7gkUhjk+AFatkAlMLuMLCW/xAtFv9u2/PIP2OT/ItHC8MBsJYDQIfxGD9mbLvN2CPBxiaNzxaDwzwGh2ccSDae2cxjxtjbB/TLmTRma9lt6bkzDuNwWHuP4eOCA3ayM86fMf7w49tte/b2Y4w3326zzu0HSj3A5jBmROCzSWBIEQLMHwirGQWjYBSMgpEIALKbYpkApf6EAAAAAElFTkSuQmCC","orcid":"https://orcid.org/0000-0003-4812-2042","institution":"Amsterdam UMC","correspondingAuthor":true,"prefix":"","firstName":"Sofie","middleName":"","lastName":"Breuking","suffix":""},{"id":483988973,"identity":"3bcdb08e-f5d2-4878-9765-636c2a55228d","order_by":1,"name":"Martijn A. Oudijk","email":"","orcid":"https://orcid.org/0000-0001-8672-4365","institution":"Amsterdam Reprod \u0026 Dev","correspondingAuthor":false,"prefix":"","firstName":"Martijn","middleName":"A.","lastName":"Oudijk","suffix":""},{"id":483988974,"identity":"08778521-a0fb-4992-899b-d3255a444407","order_by":2,"name":"Benjamin Gravesteijn","email":"","orcid":"","institution":"Amsterdam UMC","correspondingAuthor":false,"prefix":"","firstName":"Benjamin","middleName":"","lastName":"Gravesteijn","suffix":""},{"id":483988975,"identity":"0593934f-889b-44df-b565-b36a126f6912","order_by":3,"name":"Marjon de Boer","email":"","orcid":"","institution":"Amsterdam UMC","correspondingAuthor":false,"prefix":"","firstName":"Marjon","middleName":"","lastName":"de Boer","suffix":""},{"id":483988976,"identity":"ad1f60e6-dfc9-41c1-a44c-9b9c53087e06","order_by":4,"name":"Eva Pajkrt","email":"","orcid":"","institution":"Amsterdam UMC","correspondingAuthor":false,"prefix":"","firstName":"Eva","middleName":"","lastName":"Pajkrt","suffix":""},{"id":483988977,"identity":"3e8f24f1-a1ef-4e48-9a33-1b94d42dd81a","order_by":5,"name":"Frederik Hermans","email":"","orcid":"","institution":"Amsterdam UMC","correspondingAuthor":false,"prefix":"","firstName":"Frederik","middleName":"","lastName":"Hermans","suffix":""}],"badges":[],"createdAt":"2025-07-07 09:41:31","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-7063902/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-7063902/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":86670273,"identity":"539b29de-70c2-4087-b963-0fd3f98ce0e0","added_by":"auto","created_at":"2025-07-14 11:27:07","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":26836,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eParticipant flow diagram\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-7063902/v1/83cc637595d8e0d5a686c208.png"},{"id":86670278,"identity":"59896c66-cfb4-4787-8890-128f81288101","added_by":"auto","created_at":"2025-07-14 11:27:07","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":82848,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eProbability of preterm birth compared to CSI, with 95% confidence intervals\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-7063902/v1/8a2a5bf89572ee7384b4f1a6.png"},{"id":86670275,"identity":"a9a05939-bf14-4e6a-9e85-763d28071b8d","added_by":"auto","created_at":"2025-07-14 11:27:07","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":86950,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eScatter plot for correlation for cervical stiffness index with cervical length measurements\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"3.png","url":"https://assets-eu.researchsquare.com/files/rs-7063902/v1/a09c6cf9f312e2cb22ded814.png"},{"id":88552911,"identity":"28b31ed0-377e-461b-88f5-6eb9d3c79388","added_by":"auto","created_at":"2025-08-07 15:54:52","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":649162,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-7063902/v1/81797a36-fdae-4f44-aeec-2fb8a040d2d0.pdf"},{"id":86670277,"identity":"5f129164-84f3-4936-9734-6721689cfb37","added_by":"auto","created_at":"2025-07-14 11:27:07","extension":"pdf","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":433599,"visible":true,"origin":"","legend":"Associations between cervical length, cervical stiffness index (CSI), and preterm birth within 7 days","description":"","filename":"AppendixfigueS1.pdf","url":"https://assets-eu.researchsquare.com/files/rs-7063902/v1/7766ad4609d5b1c6ae80f6f9.pdf"},{"id":86670276,"identity":"f7b36315-b25c-4d51-88d5-ae0f1b324375","added_by":"auto","created_at":"2025-07-14 11:27:07","extension":"docx","order_by":2,"title":"","display":"","copyAsset":false,"role":"supplement","size":25006,"visible":true,"origin":"","legend":"","description":"","filename":"Tables.docx","url":"https://assets-eu.researchsquare.com/files/rs-7063902/v1/50f27328125937bec1684ad3.docx"}],"financialInterests":"There is \u003cb\u003eNO\u003c/b\u003e Competing Interest.","formattedTitle":"Assessment of cervical softening and the prediction of preterm birth (STIPP study); a prospective cohort study","fulltext":[{"header":"Introduction","content":"\u003cp\u003eSpontaneous preterm birth (sPTB) is a global problem and is the leading cause of perinatal and neonatal morbidity and mortality.\u003csup\u003e1, 2\u003c/sup\u003e Neonates who survive PTB are at risk for physical and developmental sequalae, representing significant burden on healthcare systems and society.\u003csup\u003e3, 4\u003c/sup\u003e\u0026nbsp;\u003c/p\u003e\n\u003cp\u003ePregnant patients frequently experience symptoms suggestive of threatened PTB. However, identification of patients at high risk for birth within seven days is challenging. Patients who are likely to deliver, require treatment with antenatal corticosteroids to improve perinatal outcomes and need to \u0026nbsp;be admitted to a center with NICU facilities depending on gestational age.\u003csup\u003e5\u003c/sup\u003e\u0026nbsp;\u003c/p\u003e\n\u003cp\u003ePrimary method for predicting the risk of birth within seven days in cases of threatened preterm birth is the measurement of cervical length using a transvaginal ultrasound. Other biomarkers, such as fetal fibronectin (fFN), phosphorylated insulin-like growth factor binding protein-1 (phIGFBP-1) or placental alpha microglobulin-1 (PAMG-1) can be used to as an addition to cervical length measurement.\u003csup\u003e6-8\u003c/sup\u003e Current identification methods are characterized by a high negative predictive value (NPV). However, this results in low positive predictive value (PPV) leading to false positive tests and unnecessary admissions.\u003csup\u003e9-11\u003c/sup\u003e By improving this risk assessment, we can avoid overtreatment, reduce healthcare costs and alleviate stress for pregnant patients. Thus,\u0026nbsp;the search continues to more accurate identification of pregnancies at risk for preterm birth among those presenting with symptoms of threatened PTB.\u003c/p\u003e\n\u003cp\u003eAlthough sPTB is a multifactorial problem with several pathophysiological pathways, clinically these all result in the final common pathway to birth: cervical softening, shortening and dilation.\u003csup\u003e12\u003c/sup\u003e These processes follow different time courses and progress in parallel rather than sequentially, suggesting that cervical softening and shortening may offer distinct or complementary insights.\u003csup\u003e13\u003c/sup\u003e\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eCervical consistency during pregnancy, is recognized as a key factor influencing cervical function.\u003csup\u003e12-16\u003c/sup\u003e Parra-Saavedra et al. found that cervical consistency, measured by ultrasound, softens and thus decreases with gestational age.\u003csup\u003e15\u003c/sup\u003e The cervical consistency was significantly lower in patients with sPTB. Other techniques, such as strain elastography and shear wave elastography, show similar trends when assessing cervical consistency.\u003csup\u003e17\u003c/sup\u003e However, technical and safety challenges, including operator-dependent variability, affect their reliability and standardization.\u003csup\u003e18, 19\u003c/sup\u003e Recently, a new method was developed to measure cervical consistency during pregnancy. This technique is based on aspiration to assess tissue elasticity and expressed as cervical stiffness index (CSI). A previous study has demonstrated that this technique provides a safe and more consistent approach than physical examinations.\u003csup\u003e20\u003c/sup\u003e Therefore, CSI measurements could potentially be a novel marker to predict sPTB and contribute to better identification of patients with an increased risk of sPTB.\u003c/p\u003e\n\u003cp\u003eThe aim of this study is to evaluate CSI to predict the risk of birth in patients presenting with symptoms of threatened PTB.\u003c/p\u003e"},{"header":"Results","content":"\u003cp\u003eBetween August 2022 and October 2024, 372 patients were screened for eligibility, of which 309 met the inclusion criteria. Finally, 163 patients (52.8%) participated the study (Figure 1).\u0026nbsp;Median gestational age was 29.6 weeks [IQR 27.2 to 31.6] at enrollment. Eighty-four (51.5%) were nulliparous and 143 (87.7%) were singletons. Median cervical length was 25.0 mm [IQR 18.0 to 32.9] (Table 1).\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eIn eight patients (4.9%), CSI measurements were unsuccessful. Two resulted from difficulties to visualize the cervix, while six were due to an inability to establish a vacuum. One patient was lost to follow-up, leaving 154 patients for further analysis.\u003c/p\u003e\n\u003cp\u003eWhen investigating three consecutive CSI measurements, discrimination decreased with the second and third measurements (Table 2). Hence, first measurement (CSI-1) was most representative, all subsequent references to CSI in this section refer to CSI-1.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eThe primary outcome occurred in 10 patients (6.5%) and CSI was significantly lower in patients delivering within seven days (Table 2; 29.0 mbar [24.3-51.8] vs. 69.0 mbar [51.0-90.8]). Discrimination for this outcome was adequate (AUC 0.77 [95% CI; 0.55-0.99]).\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eFor the secondary outcomes, lower CSI measurements were associated with higher\u0026nbsp;probabilities of birth within seven days, 14 days and sPTB before 32 weeks. Discrimination was lower for sPTB before 34 and 37 weeks (Table 2 and Figure 2).\u0026nbsp;Outcomes for birth within 48 hours and before 28 weeks occurred in only six and four patients, respectively; therefore, analyses were not performed due to low numbers.\u003c/p\u003e\n\u003cp\u003ePatients with a history of cervical surgery had higher CSI values (104.0 mbar [IQR: 83.0-117.5] versus 64.0 mbar [48.0-88.3]). Patients with cerclage placement, nulliparous and singletons have slightly higher CSI measurements (Table 3).\u003c/p\u003e\n\u003cp\u003eMinimal correlation was observed between cervical length values and CSI (\u0026rho;=0.12 95% CI -0.04 \u0026ndash; 0.28), suggesting that CSI could add new value to prediction of sPTB (Appendix).\u0026nbsp;Exploratory analysis show a group of patients with a short cervix and high CSI value did not deliver within seven days. Contrary, most sPTB occurred in the lower left quadrant indicating that patients with short a cervical length in and \u0026nbsp;low CSI are at risk for PTB (Figure 3).\u003c/p\u003e\n\u003cp\u003e\u003cem\u003eSafety and patient experience\u003c/em\u003e\u003c/p\u003e\n\u003cp\u003eNo adverse events or complications were reported. Fifty-four out of 149 patients (32.7%) reported the procedure as uncomfortable but not painful. All patients attributed this discomfort to use of the speculum, rather than the measurement itself.\u003c/p\u003e"},{"header":"Discussion","content":"\u003cp\u003eA soft cervix as quantified by a low CSI is associated with a higher risk of birth within seven days in patients with symptoms suggestive of threatened PTB.\u0026nbsp;No significant correlation was found between CSI and cervical length measurement, therefore, CSI could provide new information to predict preterm birth. \u0026nbsp;When combined with cervical length, CSI can potentially rule out patients at risk for preterm birth with a short cervix, thereby improving risk assessment.\u0026nbsp;Measurement of CSI did not report adverse events or complications.\u0026nbsp;Additionally, patients\u0026apos; experience reveals no discomfort attributed to the CSI measurement. However, one-third of the patients report discomfort due to the use of the speculum.\u003c/p\u003e\n\u003cp\u003eA study from Badir et al.\u003csup\u003e29\u003c/sup\u003e demonstrated that cervical stiffness decreases throughout normal pregnancy and has an important role in the onset of labor. Their findings suggest that early and progressive decrease in cervical stiffness is associated with a higher risk of sPTB. Similarly, Stone et al.\u003csup\u003e16\u003c/sup\u003e studied asymptomatic patients with a history of cervical insufficiency. They found that\u0026nbsp;patients undergoing ultrasound-indicated cerclage had a significantly lower CSI and thus stated measurement of cervical consistency can be a promising technique for assessment of patients at risk for cervical dysfunction.\u0026nbsp;Our study adds to these findings that lower CSI in symptomatic patients is significantly associated with higher risk of birth within seven days. This shows that cervical softening plays a crucial role in giving birth.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eThese findings are in line with other techniques, such as strain elastography and shear wave elastography, finding cervical softening to be a risk factor for preterm birth. These techniques are promising, yet currently limited by factors such as operator dependence, standardization challenges, and accessibility in clinical practice.\u003csup\u003e17\u003c/sup\u003e\u0026nbsp; CSI measurements use a different approach, using direct mechanical assessment of cervical softening, offering a objective, easily performed measurement of cervical softening.\u003c/p\u003e\n\u003cp\u003eAnother important finding in line with current literature is that CSI is affected by cervical surgery. We found higher CSI values in patients with a history of cervical surgery, suggesting that scar tissue can affect CSI. This has also been described by Stone et al.\u003csup\u003e16\u003c/sup\u003e, where they found high CSI in patients with history of cervical surgery. This highlights the need caution when interpreting the CSI measurement in this population,\u0026nbsp;as well as the importance of further research to better understand its implications.\u003c/p\u003e\n\u003cp\u003eUse of CSI in prediction of birth in patients with threatened PTB appears promising. The timeline of biomechanical changes, as reflected by CSI measurements, differs from that of cervical length, indicating that these methods may offer distinct or complementary insights. Therefore, by incorporating CSI measurements into risk assessment it could enhance targeted medical interventions. Ultimately this may lead to reduction of overtreatment and unnecessary hospitalization.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eFurther validation in larger populations is necessary to confirm these findings.\u0026nbsp;This will improve generalizability and reliability of CSI across different demographic and clinical settings. Next step should be to validate prognostic value and evaluate its incremental value over of with other clinical variables such cervical length and biomarkers (fFN, phIGFBP-1 or PAMG-1). Ultimately it should be (cost-) effective to adjust current diagnostic algorithms.\u003csup\u003e30\u003c/sup\u003e\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eIn future research, we suggest using the first CSI measurement, due to its highest discrimination, with a decrease in predictive capability seen in CSI-2 and CSI-3. Clinically, CSI-1 is also the preferred choice since it represents tissue characteristics before any deformation occurs. We discourage the use of averages of the three consecutive measurements: this combines more predictive and less predictive measurements, potentially resulting in a less predictive overall measure.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eAnother focus is applicability of CSI measurements across various etiologies of sPTB.\u003csup\u003e31\u003c/sup\u003e As previously shown by Stone et al.\u003csup\u003e16\u003c/sup\u003e, early cervical softening is a significant predictor in cases of cervical insufficiency. However, it could be hypothesized that CSI measurements have limited predictive value in twin pregnancies, where the mechanism of sPTB is more closely associated with uterine overdistension.\u003csup\u003e31\u003c/sup\u003e On the other hand, it could also be argued that regardless of the underlying cause, sPTB starts with early cervical remodeling (softening, shortening and dilatation), suggesting that the measurement may hold predictive value irrespective of the specific etiology. Consequently, it is essential to include a larger patient cohort to enable these subgroup analyses and assess the predictive value of the CSI within these diverse groups.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eA strength of this study is its design that includes predefined outcome measures and a registered protocol. The first stage has demonstrated that CSI provides predictive information regarding the risk of sPTB, offering new insights beyond cervical length. Also, this design ensures minimal interference with daily practice, making the study easier for clinicians to execute.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eAnother strength is the use of birth within seven days as the primary outcome, given its direct impact on clinical decision-making. Current methods to identify patients at high risk for birth within seven days often result in the admission and treatment of the majority of those classified as high-risk, who ultimately do not deliver. By focusing on this outcome, improvement of identification could reduce overtreatment.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eA limitation was the prevalence of sPTB within seven days that was lower than expected (6.5% versus 12.0%). One possible explanation is the fact that clinicians may be overly prone to including patients, potentially leading to the inclusion of individuals who do not actually exhibit true symptoms of threatened PTB. This may be reinforced by the inclusion criteria being primarily based on symptoms rather than objective measurements, such as cervical length or contractions on the cardiotocography. Consequently, the role of clinical judgment by healthcare professionals is overseen and the threshold for inclusion is low. Moreover, patients with severe symptoms, might avoid additional diagnostic procedures, leading to their decision to decline participation. Consistent with the fact that speculum use is widely recognized as uncomfortable, and in line with the limitations described by Stone et al.\u003csup\u003e16\u003c/sup\u003e, the requirement of speculum examination for the measurement, was identified as the primary reason for refusal. This factor may be further amplified if a patient with true, severe symptoms are at higher risk, yet choose not to participate. In future, CSI measurement might enhance targeted patient care to such an extent that patients recognize their individual benefits, making them more willing to undergo the possible discomfort of a speculum examination.\u003c/p\u003e\n\u003cp\u003eLastly, the CSI measurement is limited to\u0026nbsp;investigating a relatively small amount of cervical tissue on the ectocervix. No information is provided about mechanical properties of the internal os, where cervical shortening starts. However, a previous study\u003csup\u003e14\u003c/sup\u003e investigating the same device, concluded that the observed time course of the decrease of CSI measured on the ectocervix, parallels the compliance changes in the entire cervix as described by Parra-Saavedra et al.\u003csup\u003e15\u003c/sup\u003e\u003c/p\u003e"},{"header":"Conclusion","content":"\u003cp\u003eA soft cervix, as quantified by a low CSI, in patients presenting with symptoms of threatened PTB is associated with an increased risk of birth within seven days. The observation of no significant correlation between cervical length and CSI suggests that CSI provides new information and can potentially improve risk assessment for sPTB. Measurements of CSI could identify a group of patients with a short but stiff cervix who do not deliver within seven days. Therefore, the use of CSI measurement can potentially help in reducing unnecessary admission and overtreatment. Important next steps include determining its incremental value over cervical length and integrating it into a prediction model to better assess birth in patients facing threatened PTB.\u003c/p\u003e"},{"header":"Methods","content":"\u003cp\u003e\u003cem\u003eStudy design and participants\u003c/em\u003e\u003c/p\u003e\n\u003cp\u003eThis study is an investigator-initiated, single-center cohort study conducted at the Amsterdam University Medical Center in the Netherlands, a tertiary referral center. Recruitment started on 18\u003csup\u003eth\u003c/sup\u003e August 2022. The study was approved by the Medical Ethics Committee of Amsterdam UMC (METC2022.0226) and the protocol was prospectively registered at ClinicalTrials.gov (NCT05477381) and published. \u003csup\u003e21\u003c/sup\u003e\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eAll pregnant patients presenting with symptoms of threatened PTB, such as regular painful contractions, abdominal or back pain, vaginal bleeding, with a gestational age between 24 and 34 weeks and intact membranes, were eligible for the study.\u0026nbsp;Exclusion criteria were sings of intrauterine infection, confirmed fetal abnormalities, vasa or placenta previa and other obstetric indications requiring immediate delivery like advanced labor, cord prolapse, placental abruption, or fetal distress.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eVerbal and written informed consent were obtained from patients prior to the entry of the study.\u003c/p\u003e\n\u003cp\u003e\u003cem\u003eMethods\u003c/em\u003e\u003c/p\u003e\n\u003cp\u003eAll patients included received standard care as outlined by the Dutch Society for Obstetrics and Gynecology guideline on threatened PTB.\u003csup\u003e22\u003c/sup\u003e Standard care included cardiotocography to monitor contractions and fetal well-being, a midstream urine sample to rule out urinary tract infection, a transvaginal ultrasound to measure cervical length and a speculum exam for fFN testing.\u0026nbsp;Transvaginal cervical length was measured according to the criteria proposed by Society for Maternal and Fetal medicine (SMFM)\u003csup\u003e23\u003c/sup\u003e and International Society of Ultrasound in Obstetrics and Gynecology (ISUOG).\u003csup\u003e24\u003c/sup\u003e Patients were classified as high risk for birth within seven days if their cervical length was \u0026lt;15mm. Those with cervical lengths of 15\u0026ndash;30mm required an additional positive fFN test. Patients with a cervical length greater than 30 mm, as well as those with a cervical length of 15\u0026ndash;30 mm and a negative fFN test, were classified as low risk.\u003csup\u003e9, 25\u003c/sup\u003e High risk patients were admitted and administered antenatal corticosteroids. Tocolysis and magnesiumsulphate were advised if the gestational age was under 30 weeks.\u003csup\u003e26\u003c/sup\u003e In addition to this standard care, all patients underwent CSI measurements and completed a questionnaire.\u003c/p\u003e\n\u003cp\u003eMidway through patient recruitment, the fFN became unavailable.\u003csup\u003e27\u003c/sup\u003e This led to an adjustment in standard care for patients with a cervical length between 15-30 mm. In these patients, cervical length was repeated after two hours. If the subsequent measurement was shorter, patients were classified as high risk. Conversely, if the measurement remained the same or increased, it was classified as low risk.\u003c/p\u003e\n\u003cp\u003e\u003cem\u003eCervical stiffness index measurement\u0026nbsp;\u003c/em\u003e\u003c/p\u003e\n\u003cp\u003eCervical stiffness index was measured using the Pregnolia\u0026reg; System, which includes a control unit and a disposable, sterile probe. The control unit with integrated vacuum pump is connected to the probe with a cable. To measure CSI, the cervix was visualized with a speculum and the probe was placed on the anterior lip of the cervix. This region of interest is used in accordance with the instructions of the system since this point is the most consistently accessible throughout pregnancy, thereby improving reproducibility. The control unit generated a vacuum, pulling cervical tissue 4 mm into the probe tip. The outcome was the negative pressure in millibar (mbar) needed to deform the tissue. A higher pressure indicates stiffer tissue, and lower pressure indicates softer tissue. Cervical stiffness index was assessed with three consecutive measurements (CSI-1, CSI-2 and CSI-3, respectively) at the same location without removing the probe.\u003c/p\u003e\n\u003cp\u003eWhen only one or two measurements were available, they were included in analysis based on these measurements. If CSI-1 was missing, CSI-2 and CSI-3 were shifted forward, following a last-carried-forward approach. If all measurements were unsuccessful patients were excluded from the final analyses.\u003c/p\u003e\n\u003cp\u003eA selection of clinical staff was trained to perform the CSI measurements, to cover 24 hour availability. Treating physicians and patients were blinded to the measurement results.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cem\u003ePatient experience\u003c/em\u003e\u003c/p\u003e\n\u003cp\u003eWe also assessed the patient\u0026rsquo;s experience, specifically evaluating the acceptability and tolerability of the procedure via a questionnaire.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cem\u003eOutcome measures\u003c/em\u003e\u003c/p\u003e\n\u003cp\u003ePrimary outcome was birth within seven days after enrollment. Secondary outcomes were birth within 14 days, or sPTB before 28, 32, 34 and 37 weeks. Also, latency time defined as time between inclusion and birth, birth within 48 hours and premature prelabor rupture of membranes (PPROM) were evaluated.\u0026nbsp;Outcome measures were evaluated only when at least 10 events for a given outcome had occurred.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eSafety was assessed by registering potential complications related to the procedure, including PPROM during or immediately after measurement, significant blood loss and intrauterine infection within seven days.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cem\u003eSample size\u003c/em\u003e\u003c/p\u003e\n\u003cp\u003eThis study was conducted with a dynamical sample size. To investigate the primary objective for the first step, evaluating CSI as a single predictor for birth within seven days, a sample size of 163 patients was required.\u003csup\u003e21\u003c/sup\u003e To investigate secondary objectives, such as the incremental value of CSI to cervical length, patient recruitment will continue. Contemporary sample size calculations for developing prediction models as described by Riley et al was used.\u003csup\u003e28\u003c/sup\u003e Parameters used for calculation included (1) expected prevalence of the primary outcome, (2) expected amount of explained variance by the prediction model and (3) number of predictors (input variables). For this study, prevalence of birth within seven days (0.12 = \u0026nbsp;12%) and expected R\u003csup\u003e2\u003c/sup\u003e explained by the new model (0.45) were derived from the APOSTEL I study\u003csup\u003e9\u003c/sup\u003e, as this study had a comparable population.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cem\u003eStatistical analysis\u003c/em\u003e\u003c/p\u003e\n\u003cp\u003eBaseline characteristics are calculated using descriptive statistics. Continuous variables are reported as mean with standard deviation (SD) or median with interquartile ranges (IQR). Categorical variables will be reported as proportions.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eCharacteristics of CSI measurement were explored by comparing distributions of measures across patient characteristics that might influence cervical consistency (cerclage, nulliparity, history of cervical surgery, progesterone).\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eTo evaluate predictive ability of CSI and to select the most appropriate CSI measurement for analysis, we first compared distributions of the three CSI measurements among patients with and without outcomes of interest. Next, we fitted logistic regression models for primary and secondary outcomes, with CSI as independent variable. Area under receiver-operator-characteristic (ROC) curve (c-statistic) was calculated. Mean, 2.5\u003csup\u003eth\u003c/sup\u003e percentile, and 97.5\u003csup\u003eth\u003c/sup\u003e percentile were calculated and reported as 95% confidence interval. We selected the most relevant CSI measurement based on clinical insight together with the highest area under the ROC curve (AUC).\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eThe expected effect of the most relevant CSI measurement on our evaluated outcomes was displayed by calculating expected probability of the outcome for the range of CSI values. This was done by fitting logistic regression models with the outcomes as dependent and CSI as independent variable. We assumed a linear effect on the log-odds scale, because we did not have enough events to relax this assumption.\u003c/p\u003e\n\u003cp\u003eFinally, we explored the potential incremental value of CSI over cervical length for the primary outcome. However, since the sample size of this study was powered for investigating CSI as a single predictor only, the events in the current dataset were too low for multiple regression. Therefore, visual analysis was performed with scatterplots. The co-distribution of CSI measures and cervical length were displayed for patients with and without the primary outcome.\u003c/p\u003e\n\u003cp\u003eAnalyses were performed using R (A language and environment for statistical computing. R Foundation for Statistical Computing, Vienna, Austria), version 4.2.1.\u0026nbsp;\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eDeclaration of interest:\u003c/strong\u003e None to declare\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFunding:\u0026nbsp;\u003c/strong\u003eThis study was financially and in kind supported by Pregnolia AG. They also provided the system and the probes. The funders had no role in the study design, conduction of the study, collection, management, analysis and interpretation of the data. Also, the funder had no role in preparation, reviewing or approval of the manuscript.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eTweetable statement:\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe cervix is softer in patients with threatened preterm birth who ultimately deliver within seven days.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAcknowledgements:\u0026nbsp;\u003c/strong\u003eWe would like thanks to R. van Eekelen for his assistance in determining the appropriate statistical methods to use for the execution of this study.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthor contribution\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eSB:\u003c/strong\u003e conceptualization, data curation, formal analysis, investigation, methodology, project administration, resources, software, validation, visualization, writing \u0026ndash; original draft\u0026nbsp;\u003cstrong\u003eMO:\u003c/strong\u003e conceptualization, supervision, writing \u0026ndash; review \u0026amp; editing\u0026nbsp;\u003cstrong\u003eBG:\u0026nbsp;\u003c/strong\u003eformal analysis, investigation, methodology, writing \u0026ndash; review \u0026amp; editing\u003cstrong\u003e\u0026nbsp;MdB:\u003c/strong\u003e conceptualization, writing \u0026ndash; review \u0026amp; editing\u0026nbsp;\u003cstrong\u003eEP:\u003c/strong\u003e conceptualization, writing \u0026ndash; review \u0026amp; editing\u0026nbsp;\u003cstrong\u003eFH\u003c/strong\u003e conceptualization, data curation, methodology, supervision, writing \u0026ndash; review \u0026amp; editing.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eBlencowe H, Cousens S, Oestergaard MZ, et al. National, regional, and worldwide estimates of preterm birth rates in the year 2010 with time trends since 1990 for selected countries: a systematic analysis and implications. Lancet 2012;379:2162-72.\u003c/li\u003e\n\u003cli\u003eOhuma EO, Moller AB, Bradley E, et al. National, regional, and global estimates of preterm birth in 2020, with trends from 2010: a systematic analysis. Lancet 2023;402:1261-71.\u003c/li\u003e\n\u003cli\u003eMarlow N, Wolke D, Bracewell MA, Samara M, Group EPS. Neurologic and developmental disability at six years of age after extremely preterm birth. N Engl J Med 2005;352:9-19.\u003c/li\u003e\n\u003cli\u003eMwaniki MK, Atieno M, Lawn JE, Newton CR. Long-term neurodevelopmental outcomes after intrauterine and neonatal insults: a systematic review. Lancet 2012;379:445-52.\u003c/li\u003e\n\u003cli\u003eMcGoldrick E, Stewart F, Parker R, Dalziel SR. Antenatal corticosteroids for accelerating fetal lung maturation for women at risk of preterm birth. Cochrane Database Syst Rev 2020;12:CD004454.\u003c/li\u003e\n\u003cli\u003eIams JD, Goldenberg RL, Meis PJ, et al. The length of the cervix and the risk of spontaneous premature delivery. National Institute of Child Health and Human Development Maternal Fetal Medicine Unit Network. N Engl J Med 1996;334:567-72.\u003c/li\u003e\n\u003cli\u003eStock SJ, Horne M, Bruijn M, et al. Development and validation of a risk prediction model of preterm birth for women with preterm labour symptoms (the QUIDS study): A prospective cohort study and individual participant data meta-analysis. PLoS Med 2021;18:e1003686.\u003c/li\u003e\n\u003cli\u003eDehaene I, Lorthe E, Gurney L, et al. Accuracy of the combination of commercially available biomarkers and cervical length measurement to predict preterm birth in symptomatic women: A systematic review. Eur J Obstet Gynecol Reprod Biol 2021;258:198-207.\u003c/li\u003e\n\u003cli\u003evan Baaren GJ, Vis JY, Wilms FF, et al. Predictive value of cervical length measurement and fibronectin testing in threatened preterm labor. Obstet Gynecol 2014;123:1185-92.\u003c/li\u003e\n\u003cli\u003eVarley-Campbell J, M\u0026uacute;jica-Mota R, Coelho H, et al. Three biomarker tests to help diagnose preterm labour: a systematic review and economic evaluation. 2019;23:13.\u003c/li\u003e\n\u003cli\u003eGravett MG, Menon R, Tribe RM, et al. Assessment of current biomarkers and interventions to identify and treat women at risk of preterm birth. Front Med (Lausanne) 2024;11:1414428.\u003c/li\u003e\n\u003cli\u003eVink J, Myers K. Cervical alterations in pregnancy. Best practice \u0026amp; researchClinical obstetrics \u0026amp; gynaecology 2018;52:88-102.\u003c/li\u003e\n\u003cli\u003eMyers KM, Feltovich H, Mazza E, et al. The mechanical role of the cervix in pregnancy. J Biomech 2015;48:1511-23.\u003c/li\u003e\n\u003cli\u003eBadir S, Bajka M, Mazza E. A novel procedure for the mechanical characterization of the uterine cervix during pregnancy. J Mech Behav Biomed Mater 2013;27:143-53.\u003c/li\u003e\n\u003cli\u003eParra-Saavedra M, Gomez L, Barrero A, Parra G, Vergara F, Navarro E. Prediction of preterm birth using the cervical consistency index. Ultrasound Obstet Gynecol 2011;38:44-51.\u003c/li\u003e\n\u003cli\u003eStone J, House M. Measurement of cervical softness before cerclage placement with an aspiration-based device. Am J Obstet Gynecol MFM 2023;5:100881.\u003c/li\u003e\n\u003cli\u003eShiina T, Nightingale KR, Palmeri ML, et al. WFUMB guidelines and recommendations for clinical use of ultrasound elastography: Part 1: basic principles and terminology. Ultrasound Med Biol 2015;41:1126-47.\u003c/li\u003e\n\u003cli\u003eIssaoui M, Debost-Legrand A, Skerl K, et al. Shear wave elastography safety in fetus: A quantitative health risk assessment. Diagn Interv Imaging 2018;99:519-24.\u003c/li\u003e\n\u003cli\u003eGe W, Brooker G, Mogra R, Hyett J. Measured Hyperelastic Properties of Cervical Tissue with Shear-Wave Elastography. Sensors (Basel) 2021;22.\u003c/li\u003e\n\u003cli\u003eBadir S, Bernardi L, Feijo Delgado F, Quack Loetscher K, Hebisch G, Hoesli I. Aspiration technique-based device is more reliable in cervical stiffness assessment than digital palpation. BMC Pregnancy Childbirth 2020;20:391.\u003c/li\u003e\n\u003cli\u003eBreuking S, Oudijk MA, van Eekelen R, de Boer MA, Pajkrt E, Hermans F. Assessment of cervical softening and the prediction of preterm birth (STIPP): protocol for a prospective cohort study. BMJ Open 2023;13:e071597.\u003c/li\u003e\n\u003cli\u003eSpecialisten FM. Dreigende vroeggeboorte, 2012.\u003c/li\u003e\n\u003cli\u003eSociety for Maternal-Fetal Medicine . Electronic address pso, McIntosh J, Feltovich H, Berghella V, Manuck T. The role of routine cervical length screening in selected high- and low-risk women for preterm birth prevention. Am J Obstet Gynecol 2016;215:B2-7.\u003c/li\u003e\n\u003cli\u003eCoutinho CM, Sotiriadis A, Odibo A, et al. ISUOG Practice Guidelines: role of ultrasound in the prediction of spontaneous preterm birth. Ultrasound Obstet Gynecol 2022;60:435-56.\u003c/li\u003e\n\u003cli\u003eVis JY, Van Baaren GJ, Wilms FF, et al. Randomized comparison of nifedipine and placebo in fibronectin-negative women with symptoms of preterm labor and a short cervix (APOSTEL-I Trial). American Journal of Perinatology 2015;32:451-59.\u003c/li\u003e\n\u003cli\u003eMeliezer JAL, van der Windt LI, Ravelli ACJ, Onland W, Oudijk MA. Effects of nationwide adjustment of tocolysis protocol in the Netherlands on neonatal outcomes in women with threatened preterm birth and delivery at 30-32 weeks of gestation: A cohort study. Eur J Obstet Gynecol Reprod Biol X 2024;24:100343.\u003c/li\u003e\n\u003cli\u003eNHS England. Discontinuation of Hologic fetal fibronectin testing. 2024. https://www.england.nhs.uk/long-read/discontinuation-of-hologic-fetal-fibronectin-testing/ (accessed October 23, 2024).\u003c/li\u003e\n\u003cli\u003eRiley RD, Ensor J, Snell KIE, et al. Calculating the sample size required for developing a clinical prediction model. BMJ 2020;368:m441.\u003c/li\u003e\n\u003cli\u003eBadir S, Mazza E, Zimmermann R, Bajka M. Cervical softening occurs early in pregnancy: characterization of cervical stiffness in 100 healthy women using the aspiration technique. Prenat Diagn 2013;33:737-41.\u003c/li\u003e\n\u003cli\u003eHlatky MA, Greenland P, Arnett DK, et al. Criteria for evaluation of novel markers of cardiovascular risk: a scientific statement from the American Heart Association. Circulation 2009;119:2408-16.\u003c/li\u003e\n\u003cli\u003eRomero R, Dey SK, Fisher SJ. Preterm labor: one syndrome, many causes. Science 2014;345:760-5.\u003c/li\u003e\n\u003c/ol\u003e"},{"header":"Tables","content":"\u003cp\u003eTables 1 to 3 are available in the Supplementary Files section.\u003c/p\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":true,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"","lastPublishedDoi":"10.21203/rs.3.rs-7063902/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-7063902/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003ePreterm birth(PTB) is a global health problem and selecting pregnancies at risk is still a challenge. This study evaluates characteristics of cervical softening as a novel biomarker to predict birth in patients presenting with symptoms of threatened PTB.\u003c/p\u003e\n\u003cp\u003eThis is a single center cohort study. Pregnancies between 24\u003csup\u003e+0\u003c/sup\u003e and 34\u003csup\u003e+0\u003c/sup\u003e weeks presenting with symptoms of threatened PTB and intact membranes were included. The cervical stiffness index (CSI) was measured with the Pregnolia® System, providing a quantitative measure of tissue consistency. Lower CSI indicates a softer cervix. Primary outcome was delivery within seven days.\u003c/p\u003e\n\u003cp\u003eWe included 163 patients between August 2022 and October 2024\u003cem\u003e.\u003c/em\u003e The primary outcome occurred in 6.5% patients (n=10). Cervical stiffness index was significantly lower in patients delivering within seven days (29.0 mbar [IQR: 24.3-51.8] vs. 69.0 mbar [51.0-90.8]) and adequately discriminated between patients with and without outcome (AUC 0.77 (0.55-0.99)). No correlation between cervical length and CSI was found (ρ=0.12). Patients with a short and soft cervix are most at risk for birth within seven days.\u003c/p\u003e\n\u003cp\u003eA soft cervix, as quantified by a low CSI, in pregnancies with symptoms of threatened PTB is associated with an increased risk of birth within seven days. CSI could be used to distinguish patients with a short cervix who are at risk for preterm birth and could improve risk assessment.\u003c/p\u003e","manuscriptTitle":"Assessment of cervical softening and the prediction of preterm birth (STIPP study); a prospective cohort study","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-07-14 11:27:03","doi":"10.21203/rs.3.rs-7063902/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"15016740-d703-42cf-bc59-e51a9df90326","owner":[],"postedDate":"July 14th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[{"id":51391494,"name":"Health sciences/Medical research/Outcomes research"},{"id":51391495,"name":"Health sciences/Risk factors"}],"tags":[],"updatedAt":"2025-08-07T15:46:45+00:00","versionOfRecord":[],"versionCreatedAt":"2025-07-14 11:27:03","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-7063902","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-7063902","identity":"rs-7063902","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}