Uterocervical angle and cervical length measurements for preterm birth prediction in low-risk singleton pregnant women: A prospective cohort study

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Strategies to predict preterm birth risk can help improve pregnancy outcomes. Even pregnant women without known risk factors for preterm birth can also experience it. This study aimed to evaluate the ability of the uterocervical angle and cervical length to predict preterm birth in low-risk singleton pregnant women. Methods A prospective study of 1,107 singleton pregnant women between 16 + 0 and 23 + 6 weeks gestation at low risk for preterm birth who were treated at the Haiphong Hospital of Obstetrics and Gynecology, Vietnam, between September 2020 and September 2021 was conducted. A single sonographer assessed the cervical length and the uterocervical angle using transvaginal ultrasonography. The patients were followed up until delivery to determine the main pregnancy outcome (preterm birth before 37 weeks gestation). The cut-off points for the uterocervical angle and cervical length were established by analysing the receiver operating characteristic curve. The sensitivity, specificity, likelihood ratio, and positive and negative predictive values of the uterocervical angle and cervical length for predicting preterm birth were determined. Results A uterocervical angle ≥ 98.86° predicted preterm birth at < 37 weeks, with a sensitivity and specificity of 91% and 75.5%, respectively. A cervical length ≤ 33.8 mm predicted preterm birth at < 37 weeks with a sensitivity and specificity of 25% and 66%, respectively. A uterocervical angle ≥ 98.96 ° combined with a cervical length ≤ 33.8 mm increased the positive predictive value, positive likelihood ratio, and accuracy of preterm birth prediction to 36%, 8.87, and 91%, respectively. Conclusion Compared to the cervical length, the uterocervical angle can be considered a valuable ultrasound parameter for predicting preterm birth in low-risk singleton pregnant women. Combining both the uterocervical angle and cervical length yielded stronger preterm birth prediction values. Uterocervical angle Cervical length Preterm birth Low risk Singleton pregnancy Figures Figure 1 Figure 2 Figure 3 Figure 4 What does this study add to the clinical work 1. Pregnant women without known risk factors for preterm birth can also experience preterm birth. 2. In comparison to cervical length, the uterocervical angle can be considered a valuable ultrasound parameter for predicting preterm birth in low-risk singleton pregnant women. Combining both the uterocervical angle and cervical length yielded stronger preterm birth prediction values. Introduction According to the World Health Organization, preterm birth is defined as birth before 37 completed weeks of gestation. Approximately 15 million babies are born prematurely each year globally, with more than 60% of preterm births occurring in Africa and South Asia [ 1 ]. In Vietnam, the preterm birth rate is 9%, ranking 21st worldwide [ 2 ]. Spontaneous preterm birth accounts for approximately two-thirds of all preterm births and continues to be a major challenge in obstetrics. Spontaneous preterm birth is the primary cause of early neonatal morbidity and mortality, primarily due to the presence of underdeveloped respiratory organs, brain haemorrhage, and infection. These complications can have long-term neurological consequences, including intellectual impairment, cerebral palsy, chronic lung disease, and visual and auditory impairment [ 3 ]. To reduce the risk of complications associated with preterm birth, various prediction strategies have been proposed to enable the use of preventive measures that can improve pregnancy outcomes. A history of preterm birth is considered the most important risk factor for subsequent preterm birth. Nevertheless, a history of preterm birth is only present in approximately 10% of women with preterm births occurring before 34 weeks of gestation [ 4 , 5 ]. Several scoring systems for preterm birth risk rely solely on a history of preterm birth, leading to limitations in accuracy and reproducibility across different populations [ 6 ]. Currently, the measurement of cervical length through transvaginal ultrasound in the second trimester is the most common screening strategy. In the case of a positive finding, vaginal progesterone treatment is highly recommended for preventing preterm birth [ 7 , 8 ]. For singleton pregnancies, a cervical length of 25 mm or less is considered to increase the risk of preterm birth; however, the preterm birth detection rate before 32 weeks of gestation is only approximately 55%, with a false-positive rate of 10% [ 9 , 10 ]. In recent years, the uterocervical angle has been proposed as a potential ultrasound parameter for predicting preterm birth [ 11 ]. When the uterocervical angle is obtuse, the cervical canal is more affected by the gravitational force from the uterus and foetus, leading to the gradual shortening and dilatation of the cervix [ 12 , 13 ]. It has been reported that combining the uterocervical angle with cervical length improves preterm birth prediction [ 14 , 15 ]. The primary focus of previous research concerning the prediction of preterm birth has been a prior history of preterm birth and short cervical length. However, pregnant women without known risk factors for preterm birth can also experience preterm birth, with a rate of approximately 8% [ 16 ]. To date, very few studies have evaluated the prognostic value of the uterocervical angle and cervical length for predicting preterm birth in low-risk pregnant women. Accordingly, this study aimed to evaluate the effectiveness of the uterocervical angle and cervical length for predicting preterm birth in low-risk singleton pregnant women. Methods Study design This was a prospective cohort study conducted at the Department of Pregnancy Management and Prenatal Diagnosis of Haiphong Hospital of Obstetrics and Gynecology, Vietnam, from September 2020 to September 2021. Sample size calculation The sample size equation for estimating the sensitivity of a test was used to calculate the sample size for this study as follows: $$n=\frac{\frac{{Z}_{1-\raisebox{1ex}{$\alpha $}\!\left/ \!\raisebox{-1ex}{$2$}\right.}^{2}Sens (1-Sens)}{{d}^{2}}}{Prev}$$ For which: α: type I error (α = 0.05). Sens: the estimated sensitivity of the uterocervical angle test (Sens = 0.83) [ 16 ]. d: the estimated margin of error (d = 0.1). Prev: the prevalence of preterm birth in the general population (Prev = 0.81) [ 16 ]. Based on these values, the minimum sample size was 680 participants. This study included 1,107 pregnant women. Study population All singleton pregnant women aged 18–40 years between 16 + 0 and 23 + 6 weeks gestation who had living foetuses and were treated at the Haiphong Hospital of Obstetrics and Gynecology, Vietnam, from September 2020 to September 2021 were counselled and invited to participate in this study. Gestational age was determined by the first day of the last menstrual period or by the expected date of birth determined via ultrasound in the first trimester. The exclusion criteria included women who had one or more of the following high-risk factors for preterm birth (PTB): (1) a history of PTB or second-trimester miscarriage (miscarriage at 13 + 0 − 19 + 6 weeks gestation) [ 17 ], (2) a cervical length ≤ 25 mm, (3) a history of cervical surgery (conization, loop electrosurgical excision procedure (LEEP)), (4) signs of threatened miscarriage or PTB, (5) medically indicated PTB or (6) loss to follow-up. A total of 1,228 singleton pregnant women at 16 + 0 − 23 + 6 weeks gestation voluntarily participated in the study. Each patient underwent cervical length and uterocervical angle measurements once at the time of examination and was closely followed up to delivery. The demographic information of the participants was collected and documented at the time of recruitment. Pregnancy and neonatal outcomes were recorded in electronic medical records. Women who gave birth at hospitals other than the study site were contacted by phone. After excluding 121 pregnant women who were either at high risk of PTB, had a medical indication for PTB, or were lost to follow-up, the final study population included 1,107 pregnant women. Assessment of cervical length and the uterocervical angle Cervical length (CL) and uterocervical angle (UCA) measurements were performed transvaginally by a single doctor who was certified and monitored by the Foetal Medicine Foundation using Samsung Hera W10 (Korea) and GE Voluson E6 (GE Healthcare Korea) ultrasound machines with a 7.5–10 MHz endovaginal probe. The pregnant woman was placed in the dorsal lithotomy position with an empty bladder. The probe was placed into the anterior fornix of the vagina and positioned so that the endocervical canal could be visualized without excessive pressure. The cervix accounts for approximately 50–75% of the images and should be measured along its longitudinal axis. For CL measurements, a straight line was drawn from the internal to the external cervical os [ 18 ]. Three CL measurements were obtained, and the shortest value was recorded (Fig. 1a). The UCA was defined as the angle between the two lines and was assessed according to the technique described by Dziados et al. [ 14 ]: the first line was drawn from the external to the internal os of the cervix, and the second line was drawn tangentially to the anterior wall of the lower uterine segment, passing through the internal cervical os. Three UCA measurements were obtained, and the greatest value was used for analysis (Fig. 1b). Outcome measures The main outcome of this study was preterm birth before 37 weeks gestation. Ethical considerations The study was approved by the Ethical Council in Biomedical Research of Hue University of Medicine and Pharmacy, Vietnam (Ethics Committee ID number H2020/035) and the Scientific Council of Haiphong Hospital of Obstetrics and Gynecology, Vietnam (IEC, 1186/QD-BVPSHP). All the participants were fully informed about the study, and written informed consent was obtained before any procedures were conducted. Statistical analysis SPSS version 20.0 was used for the statistical analysis. The categorical variables are reported as numbers and percentages, and the continuous variables are reported as the mean and standard deviation. The Kolmogorov‒Smirnov test was used to determine the distribution of the data. The chi-square test was used to compare the distribution of categorical data, and Student’s t test or the Mann‒Whitney U test was used to test the difference between two means. The correlations between the UCA and CL values and gestational age at delivery were evaluated with the Pearson chi-square correlation coefficient. Receiver operating characteristic (ROC) curves were used to assess the ability of the UCA and CL to predict PTB and determine the appropriate cut-off point to provide maximum sensitivity (Se) and specificity (Sp). Multivariate logistic regression adjusted for UCA, CL, maternal age, and obstetric history was performed to determine the associations of the UCA and CL with preterm birth at the cut-off points. A p value < 0.05 was considered to indicate statistical significance. Results Table 1 General characteristics of the study participants (n = 1,107). Characteristics n (%) or median Full-term birth (≥ 37 weeks) (n = 1.040) Preterm birth < 37 weeks (n = 67) p value Maternal characteristics Maternal age (years) 28.83 ± 5.12 29.27 ± 5.24 0.501 * Obstetric history Nulliparous 444 (42.7%) 24 (35.8%) 0.523 ** Multiparous 595 (57.2%) 43 (64.2%) Gestational age at TVS (weeks) 19.96 ± 2.42 21.20 ± 1.90 < 0.001 * CL at TVS (mm) 36.35 ± 5.07 32.06 ± 4.19 < 0.001 * UCA at TVS (degrees) 82.41 ± 12.10 119.41 ± 18.46 < 0.001 * Neonatal characteristics and outcomes Gestational age at birth (weeks) 38.74 ± 0.87 34.93 ± 1.68 < 0.001 * Birth weight (grams) 3178.13 ± 284.47 2446.27 ± 404.64 < 0.001 * C-section delivery 429 (41.3%) 11 (16.4%) < 0.001 ** NICU admission 31 (3.0%) 35 (52.2%) < 0.001 ** Deaths 0 1 (1.5%) NA *Student’s t test, **chi-square test. SD: standard deviation; TVS: transvaginal ultrasound; CL: cervical length; UCA: uterocervical angle; NICU: neonatal intensive care unit; NA: not applicable. Among the 1,107 participants at low risk for preterm birth included in our study, 67 had spontaneous PTB at < 37 weeks (6.05%). The mean UCA at ultrasound was significantly greater in the preterm birth group (119.41 ± 18.46 degrees) than in the term group (82.41 ± 12.10 degrees) (p < 0.001). In addition, the mean CL was significantly shorter in pregnant women in the preterm group (32.06 ± 4.19 mm) than in those in the term group (36.35 ± 5.07 mm) (p < 0.001). The areas under the curve (AUCs) of the UCA and CL were 0.899 (95% CI: 0.872–0.926) and 0.240 (95% CI: 0.176–0.304), respectively (Fig. 3 ). There was a significant positive correlation between CL and gestational age at delivery (r = 0.159, p < 0.001) and a significant negative correlation between the UCA and gestational age at delivery (r = -0.396, p < 0.001) (Fig. 4 ). Table 2 The association among the UCA, CL, and preterm birth at < 37 weeks at the UCA and CL cut-off points. Parameter beta OR 95% CI p UCA ≥ 98.96 ° a 3.571 35.56 14.88–84.96 < 0.001 CL ≤ 33.8 mm b 2.626 13.82 6.52–29.29 < 0.001 UCA ≥ 98.96 ° and CL ≤ 33.8 mm c 3.190 24.28 13.90-42.41 < 0.001 a adjusted for CL, maternal age, and obstetric history b adjusted for UCA, maternal age, and obstetric history Adjusted for maternal age and obstetric history Logistic regression analysis revealed that a UCA ≥ 98.96 ° , a CL ≤ 33.8 mm, and the combination of a UCA ≥ 98.96 ° and a CL ≤ 33.8 mm were significantly associated with preterm birth at < 37 weeks, with ORs (95% CIs) of 35.56 (14.88–84.96), 13.82 (6.52–29.29), and 24.28 (13.90-42.41), respectively (Table 2 ). Table 3 Diagnostic performance of the UCA and CL for predicting preterm birth at < 37 weeks at the UCA and CL cut-off points. Parameter Se Sp PPV NPV LR+ LR- ACC UCA ≥ 98.96 ° 0.91 0.75 0.193 0.99 3.71 0.12 0.76 CL ≤ 33.8 mm 0.25 0.66 0.046 0.93 0.75 1.13 0.63 UCA ≥ 98.96 ° and CL ≤ 33.8 mm 0.66 0.93 0.36 0.98 8.87 0.37 0.91 The optimal UCA cut-off for predicting preterm birth at < 37 weeks according to the ROC curve was 98.96 ° , with a sensitivity (Se) and specificity (Sp) of 91% and 75.5%, respectively. In addition, at a cut-off point of 33.8 mm, the Se and Sp of the CL for predicting preterm birth at < 37 weeks were 25% and 66%, respectively. Moreover, the use of both a UCA ≥ 98.96 ° and CL ≤ 33.8 mm increased the positive predictive value (PPV), positive likelihood ratio (LR+), and accuracy (ACC) for the prediction of preterm birth at < 37 weeks to 36%, 8.87, and 91%, respectively (Table 3 ). Discussion Among the 1,107 low-risk participants included in our study, 6.05% gave birth at < 37 weeks, which is lower than that reported in previous studies [ 19 , 20 ]. As shown in Table 1 , the mean CL was significantly shorter in the participants who delivered preterm than in those who delivered at term, and the mean UCA was significantly greater in those who delivered preterm. These results were in agreement with the findings of previous studies conducted in unselected singleton pregnant women; the UCA was significantly wider in singleton pregnant women with spontaneous PTB [ 21 – 25 ]. The combination of pressure applied by the surrounding pelvic organs, more importantly from the growing uterus during pregnancy, could result in the alteration of the internal ostium (os) and cervical function [ 26 ]. Some ultrasonographic parameters, such as the CL and UCA, have been used to assess cervical structure. In this regard, it can be said that an obtuse cervical angle is associated with a straight and direct force from the pregnant uterus, while an acute cervical angle is associated with a less direct force, maintaining the integrity of the cervix. In other words, the hypothesis is that the cervical angle acts as a barrier that affects the progression of labour when the angle is acute [ 12 , 27 , 28 ]. Our study revealed that the optimal UCA and CL cut-off values for predicting PTB at < 37 gestational weeks in low-risk participants were 98.96 degrees and 33.8 mm, respectively, which were similar to the results reported by Minoo Movahedi et al. [ 29 ], who recruited patients using the same criteria. In their study, the UCA and CL thresholds for PTB prediction were found to be 106° and 33 mm, respectively. These results were also consistent with the recent study by M Zhang et al. [ 30 ] on 275 singleton pregnancies in early and mid-pregnancy, that showed the optimal threshold of UCA and CL to predict PTB < 37 weeks gestation was 96° and 33.8 mm, respectively. Additionally, Sawaddisan et al. [ 16 ] reported that a UCA ≥ 110° measured later than 19.5 weeks of gestation corresponded to an 83.3% sensitivity for predicting spontaneous PTB. A study conducted by Paul Guerby et al. [ 31 ] revealed that a mid-trimester CL < 30 mm could detect 35% of all spontaneous PTBs before 35 weeks gestation at a false-positive rate of 5% in low-risk nulliparous women. It is important to note that their study included only women with no previous pregnancies, and ultrasound was conducted between 20 and 24 weeks gestation. Our findings also demonstrated that at the cut-off points, a UCA ≥ 98.96°, a CL ≤ 33.8 mm, and the combination of a UCA ≥ 98.96 ° and a CL ≤ 33.8 mm were significantly associated with PTB at < 37 weeks gestation, with ORs (95% CIs) of 35.56 (14.88–84.96), 13.82 (6.52–29.29), and 24.28 (13.90-42.41), respectively. Nonetheless, our study of low-risk pregnant women showed that CL alone did not have a significant impact on predicting PTB, unlike in the general population. A CL of 33.88 mm or less was a poor predictor for PTB, with a low sensitivity of 25%, a specificity of 66%, and an area under the curve (AUC) of only 0.240 (95% CI: 0.176–0.304). Jeanine van der Ven et al. [ 32 ] also reported that mid-trimester CL measurements had limited value for predicting spontaneous PTB in a large population of low-risk singleton pregnant women from 16 + 0 -21 + 6 weeks gestation, with a poor AUC of 0.56 (95% CI 0.52–0.6) for PTB before 37 weeks gestation. This finding was consistent with a previous study by Iams et al. [ 33 ], which revealed that the positive predictive value of CL was poor (ranging from 6 to 44%), and the sensitivity was only 47% in a low-risk population. In contrast, the UCA could be used as a predictive tool to identify women at risk of PTB in this low-risk population. The UCA alone had greater sensitivity and specificity than the CL, with a UCA of 98.96 degrees or more having a sensitivity and specificity of 91% and 75%, respectively. In addition, the AUC of the UCA was 0.899, which performed well in identifying women at risk of PTB in our study population. This finding contradicts the results reported by Sawaddisan et al. [ 16 ], who reported that the UCA in the second trimester is not a good predictor of PTB in low-risk pregnant women. The discrepancy in the findings may arise from the smaller sample size examined in their study compared to that in our study. In a recent systematic review, Goldstein et al. [ 21 ] analysed 15 studies that provided data on the test characteristics of the UCA and CL for predicting PTB. The review revealed that for the general population, the UCA alone had a significantly greater sensitivity (0.70; 95% CI: 0.66–0.73) than CL (0.46; 95% CI: 0.42–0.49). However, the UCA also had a significantly lower specificity (0.67; 95% CI: 0.66–0.68) than CL (0.90; 95% CI: 0.89–0.91) and a lower AUC (0.77) than CL (0.82). Remarkably, our findings showed that while CL alone was not a reliable predictor of preterm birth in this low-risk population, combining CL with the UCA improved the predictive value compared to the UCA alone. The use of both a UCA ≥ 98.96 ° and a CL ≤ 33.8 mm increased the positive predictive value (PPV), positive likelihood ratio (LR+), and accuracy (ACC) for the prediction of PTB at < 37 weeks gestation to 36%, 8.87, and 91%, respectively, which agreed with the results reported in previous studies [ 14 , 34 ]. Measuring the UCA at the same time as the CL for screening PTB according to recommendations (at a gestational age of 16–24 weeks) is convenient in clinical practice and may increase the effectiveness of PTB prediction when combining these two parameters. The main strength of this study is that it is the first study conducted among low-risk singleton pregnant women in Vietnam, with a large sample size that demonstrated the ability of the UCA and CL to predict preterm birth. However, even when multivariate logistic regression was used to assess the associations among the UCA, CL, and preterm birth, we cannot deny that other factors may have influenced the outcome of preterm birth, such as smoking status and type of conception. Further multicentre studies are required to evaluate the consistency of these results and establish definitive conclusions. Conclusion The results of this study suggest that, compared with cervical length alone, the uterocervical angle measured during the second trimester via transvaginal ultrasound could be a valuable parameter for predicting preterm birth in low-risk singleton pregnant women. The use of the combination of the uterocervical angle and cervical length yielded stronger preterm birth prediction values. Declarations Acknowledgments The authors would like to thank all the pregnant women who agreed to participate in this study. Authors contributions N.T.H.T., V.V.T., and N.V.Q.H. designed the study. N.T.H.T. and V.V.T. performed data collection. N.T.H.T. and N.V.Q.H. performed statistical analyses and wrote the first manuscript. N.T.H.T., V.V.T., and N.V.Q.H. critically revised successive drafts of the paper. All authors read and approved the final manuscript. Funding This research did not receive specific grants from funding agencies in the public, commercial, or nonprofit sectors. Data Availability The dataset used and/or analyzed during the current study are available from the corresponding author upon reasonable request. Conflict of interest The authors declare that they have no conflict of interest. Ethical approval The research proposal was approved by the Ethical Council in Biomedical Research of Hue University of Medicine and Pharmacy, Vietnam (Ethics Committee ID number H2020/035) and the Scientific Council of Haiphong Hospital of Obstetrics and Gynecology, Vietnam (IEC, 1186/QĐ-BVPSHP). 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Am J Perinatol, 2023. 40 (2): p. 187-193. van der Ven, J., et al., The capacity of mid-pregnancy cervical length to predict preterm birth in low-risk women: a national cohort study. Acta Obstetricia et Gynecologica Scandinavica, 2015. 94 (11): p. 1223-1234. Iams, J.D., et al., The Length of the Cervix and the Risk of Spontaneous Premature Delivery. New England Journal of Medicine, 1996. 334 (9): p. 567-573. Knight, J.C., et al., Uterocervical Angle Measurement Improves Prediction of Preterm Birth in Twin Gestation. Am J Perinatol, 2018. 35 (7): p. 648-654. Cite Share Download PDF Status: Published Journal Publication published 17 Jul, 2024 Read the published version in Archives of Gynecology and Obstetrics → Version 1 posted Reviewers agreed at journal 09 Apr, 2024 Reviewers invited by journal 01 Apr, 2024 Editor invited by journal 29 Mar, 2024 Editor assigned by journal 29 Mar, 2024 First submitted to journal 28 Mar, 2024 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 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-4184828","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":286103893,"identity":"dd524c72-f43e-4437-9b70-781f6188346a","order_by":0,"name":"Trang Nguyen Nguyen Thi Hoang","email":"","orcid":"","institution":"","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Trang","middleName":"Nguyen Nguyen Thi","lastName":"Hoang","suffix":""},{"id":286103894,"identity":"c0fb6730-a4b3-433c-a589-ae215364dd27","order_by":1,"name":"Tam Vu Van","email":"","orcid":"","institution":"","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Tam","middleName":"Vu","lastName":"Van","suffix":""},{"id":286103895,"identity":"0919dc54-ffc3-4927-a634-dd4f71d4520b","order_by":2,"name":"Vu Quoc Huy Nguyen","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA/UlEQVRIiWNgGAWjYHACNiC2SQAzeaBcMIOAljTStRxGaEFlYAHmEsnbHvO2nc8zON6d+OANw+E8PokExgdv2xgSt+PQYjkjrdyYt+12scGZs5sN5zAcLmaTSGA2nAvUsrMBuxaDM2fMpIFaEjfcyN0mzfvvcGIbzwE2oAiDscEBvFrOJW64/3b7bx4GsBb233i1HO8BaTkAtIV3GzNYC3sDGzNQixxuLW1lknPOJSfOPJO7WXIOQzpQS2MzUEQCt5bDzNsk3pTZJfYdP7vxwxsG68T5zcwHP7wps+HBpQWki4GRDUWAsQFISOBUD9bC8Aef/CgYBaNgFIx4AAASGVuBT4SqsgAAAABJRU5ErkJggg==","orcid":"https://orcid.org/0000-0002-4744-7059","institution":"Hue University of Medicine and Pharmacy","correspondingAuthor":true,"submittingAuthor":false,"prefix":"","firstName":"Vu","middleName":"Quoc Huy","lastName":"Nguyen","suffix":""}],"badges":[],"createdAt":"2024-03-29 00:27:38","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-4184828/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-4184828/v1","draftVersion":[],"editorialEvents":[{"content":"https://doi.org/10.1007/s00404-024-07646-4","type":"published","date":"2024-07-17T16:05:05+00:00"}],"editorialNote":"","failedWorkflow":false,"files":[{"id":54182488,"identity":"ad3d78d1-9535-48e2-9547-0be0894d6b99","added_by":"auto","created_at":"2024-04-05 16:47:32","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":273626,"visible":true,"origin":"","legend":"\u003cp\u003e(a) TVS CL measurement: measured between the external os (E) and internal os (I); (b) TVS UCA measurement: measurement of the angle between the cervical canal and the lower uterine segment.\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-4184828/v1/39c6b21ae9e4b3a712946920.png"},{"id":54182099,"identity":"1e365e77-19bd-43fe-9ead-8ae8490daaff","added_by":"auto","created_at":"2024-04-05 16:39:32","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":40613,"visible":true,"origin":"","legend":"\u003cp\u003eStudy diagram.\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-4184828/v1/2744fd95a80bb2c3d51385db.png"},{"id":54182096,"identity":"d31948ca-2b17-4fb0-a32d-5e876c788a6e","added_by":"auto","created_at":"2024-04-05 16:39:32","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":129731,"visible":true,"origin":"","legend":"\u003cp\u003eThe receiver operating characteristic curves for UCA, CL, and preterm birth at \u0026lt;37 weeks.\u003c/p\u003e","description":"","filename":"3.png","url":"https://assets-eu.researchsquare.com/files/rs-4184828/v1/7ad413ff69668b4a7dc3bb1a.png"},{"id":54182098,"identity":"9b183885-274f-48b2-a3fe-5581cbb2a4b3","added_by":"auto","created_at":"2024-04-05 16:39:32","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":72220,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003ea.\u003c/strong\u003e Correlation between CL and gestational age at delivery.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eb.\u003c/strong\u003e The correlation between the UCA and gestational age at delivery.\u003c/p\u003e","description":"","filename":"4.png","url":"https://assets-eu.researchsquare.com/files/rs-4184828/v1/d4ddf333b1e6c2f708c2b3ff.png"},{"id":61594714,"identity":"1e18c6ba-5530-4755-bc6f-605865fe02a3","added_by":"auto","created_at":"2024-08-01 17:16:28","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":1082863,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-4184828/v1/3c39abb9-c7f5-41e1-974d-05a773bc12cc.pdf"}],"financialInterests":"","formattedTitle":"Uterocervical angle and cervical length measurements for preterm birth prediction in low-risk singleton pregnant women: A prospective cohort study","fulltext":[{"header":"What does this study add to the clinical work","content":"\u003cp\u003e1. Pregnant women without known risk factors for preterm birth can also experience preterm birth.\u003c/p\u003e\n\u003cp\u003e2. In comparison to cervical length, the uterocervical angle can be considered a valuable ultrasound parameter for predicting preterm birth in low-risk singleton pregnant women. Combining both the uterocervical angle and cervical length yielded stronger preterm birth prediction values.\u003c/p\u003e"},{"header":"Introduction","content":"\u003cp\u003eAccording to the World Health Organization, preterm birth is defined as birth before 37 completed weeks of gestation. Approximately 15\u0026nbsp;million babies are born prematurely each year globally, with more than 60% of preterm births occurring in Africa and South Asia [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e]. In Vietnam, the preterm birth rate is 9%, ranking 21st worldwide [\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e]. Spontaneous preterm birth accounts for approximately two-thirds of all preterm births and continues to be a major challenge in obstetrics. Spontaneous preterm birth is the primary cause of early neonatal morbidity and mortality, primarily due to the presence of underdeveloped respiratory organs, brain haemorrhage, and infection. These complications can have long-term neurological consequences, including intellectual impairment, cerebral palsy, chronic lung disease, and visual and auditory impairment [\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eTo reduce the risk of complications associated with preterm birth, various prediction strategies have been proposed to enable the use of preventive measures that can improve pregnancy outcomes. A history of preterm birth is considered the most important risk factor for subsequent preterm birth. Nevertheless, a history of preterm birth is only present in approximately 10% of women with preterm births occurring before 34 weeks of gestation [\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e, \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e]. Several scoring systems for preterm birth risk rely solely on a history of preterm birth, leading to limitations in accuracy and reproducibility across different populations [\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e]. Currently, the measurement of cervical length through transvaginal ultrasound in the second trimester is the most common screening strategy. In the case of a positive finding, vaginal progesterone treatment is highly recommended for preventing preterm birth [\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e, \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e]. For singleton pregnancies, a cervical length of 25 mm or less is considered to increase the risk of preterm birth; however, the preterm birth detection rate before 32 weeks of gestation is only approximately 55%, with a false-positive rate of 10% [\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e, \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eIn recent years, the uterocervical angle has been proposed as a potential ultrasound parameter for predicting preterm birth [\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e]. When the uterocervical angle is obtuse, the cervical canal is more affected by the gravitational force from the uterus and foetus, leading to the gradual shortening and dilatation of the cervix [\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e, \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e]. It has been reported that combining the uterocervical angle with cervical length improves preterm birth prediction [\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e, \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e]. The primary focus of previous research concerning the prediction of preterm birth has been a prior history of preterm birth and short cervical length. However, pregnant women without known risk factors for preterm birth can also experience preterm birth, with a rate of approximately 8% [\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e]. To date, very few studies have evaluated the prognostic value of the uterocervical angle and cervical length for predicting preterm birth in low-risk pregnant women. Accordingly, this study aimed to evaluate the effectiveness of the uterocervical angle and cervical length for predicting preterm birth in low-risk singleton pregnant women.\u003c/p\u003e"},{"header":"Methods","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e\n \u003ch2\u003eStudy design\u003c/h2\u003e\n \u003cp\u003eThis was a prospective cohort study conducted at the Department of Pregnancy Management and Prenatal Diagnosis of Haiphong Hospital of Obstetrics and Gynecology, Vietnam, from September 2020 to September 2021.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec4\" class=\"Section2\"\u003e\n \u003ch2\u003eSample size calculation\u003c/h2\u003e\n \u003cdiv class=\"BlockQuote\"\u003e\n \u003cp\u003eThe sample size equation for estimating the sensitivity of a test was used to calculate the sample size for this study as follows:\u003c/p\u003e\n \u003c/div\u003e\n \u003cdiv id=\"Equa\" class=\"Equation\"\u003e\n \u003cdiv class=\"mathdisplay\" id=\"FileID_Equa\" name=\"EquationSource\"\u003e$$n=\\frac{\\frac{{Z}_{1-\\raisebox{1ex}{$\\alpha $}\\!\\left/ \\!\\raisebox{-1ex}{$2$}\\right.}^{2}Sens (1-Sens)}{{d}^{2}}}{Prev}$$\u003c/div\u003e\n \u003c/div\u003e\n \u003cdiv class=\"BlockQuote\"\u003e\n \u003cp\u003eFor which:\u003c/p\u003e\n \u003cp\u003e\u0026alpha;: type I error (\u0026alpha;\u0026thinsp;=\u0026thinsp;0.05).\u003c/p\u003e\n \u003cp\u003eSens: the estimated sensitivity of the uterocervical angle test (Sens\u0026thinsp;=\u0026thinsp;0.83) [\u003cspan class=\"CitationRef\"\u003e16\u003c/span\u003e].\u003c/p\u003e\n \u003cp\u003ed: the estimated margin of error (d\u0026thinsp;=\u0026thinsp;0.1).\u003c/p\u003e\n \u003cp\u003ePrev: the prevalence of preterm birth in the general population (Prev\u0026thinsp;=\u0026thinsp;0.81) [\u003cspan class=\"CitationRef\"\u003e16\u003c/span\u003e].\u003c/p\u003e\n \u003cp\u003eBased on these values, the minimum sample size was 680 participants. This study included 1,107 pregnant women.\u003c/p\u003e\n \u003c/div\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec5\" class=\"Section2\"\u003e\n \u003ch2\u003eStudy population\u003c/h2\u003e\n \u003cp\u003eAll singleton pregnant women aged 18\u0026ndash;40 years between 16\u003csup\u003e+\u0026thinsp;0\u003c/sup\u003e and 23\u003csup\u003e+\u0026thinsp;6\u003c/sup\u003e weeks gestation who had living foetuses and were treated at the Haiphong Hospital of Obstetrics and Gynecology, Vietnam, from September 2020 to September 2021 were counselled and invited to participate in this study.\u003c/p\u003e\n \u003cp\u003eGestational age was determined by the first day of the last menstrual period or by the expected date of birth determined via ultrasound in the first trimester.\u003c/p\u003e\n \u003cp\u003eThe exclusion criteria included women who had one or more of the following high-risk factors for preterm birth (PTB): (1) a history of PTB or second-trimester miscarriage (miscarriage at 13\u003csup\u003e+\u0026thinsp;0\u003c/sup\u003e \u0026minus;\u0026thinsp;19\u003csup\u003e+\u0026thinsp;6\u003c/sup\u003e weeks gestation) [\u003cspan class=\"CitationRef\"\u003e17\u003c/span\u003e], (2) a cervical length\u0026thinsp;\u0026le;\u0026thinsp;25 mm, (3) a history of cervical surgery (conization, loop electrosurgical excision procedure (LEEP)), (4) signs of threatened miscarriage or PTB, (5) medically indicated PTB or (6) loss to follow-up.\u003c/p\u003e\n \u003cp\u003eA total of 1,228 singleton pregnant women at 16\u003csup\u003e+\u0026thinsp;0\u003c/sup\u003e \u0026minus;\u0026thinsp;23\u003csup\u003e+\u0026thinsp;6\u003c/sup\u003e weeks gestation voluntarily participated in the study. Each patient underwent cervical length and uterocervical angle measurements once at the time of examination and was closely followed up to delivery.\u003c/p\u003e\n \u003cp\u003eThe demographic information of the participants was collected and documented at the time of recruitment. Pregnancy and neonatal outcomes were recorded in electronic medical records. Women who gave birth at hospitals other than the study site were contacted by phone. After excluding 121 pregnant women who were either at high risk of PTB, had a medical indication for PTB, or were lost to follow-up, the final study population included 1,107 pregnant women.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec6\" class=\"Section2\"\u003e\n \u003ch2\u003eAssessment of cervical length and the uterocervical angle\u003c/h2\u003e\n \u003cp\u003eCervical length (CL) and uterocervical angle (UCA) measurements were performed transvaginally by a single doctor who was certified and monitored by the Foetal Medicine Foundation using Samsung Hera W10 (Korea) and GE Voluson E6 (GE Healthcare Korea) ultrasound machines with a 7.5\u0026ndash;10 MHz endovaginal probe. The pregnant woman was placed in the dorsal lithotomy position with an empty bladder. The probe was placed into the anterior fornix of the vagina and positioned so that the endocervical canal could be visualized without excessive pressure. The cervix accounts for approximately 50\u0026ndash;75% of the images and should be measured along its longitudinal axis. For CL measurements, a straight line was drawn from the internal to the external cervical os [\u003cspan class=\"CitationRef\"\u003e18\u003c/span\u003e]. Three CL measurements were obtained, and the shortest value was recorded (Fig.\u0026nbsp;1a). The UCA was defined as the angle between the two lines and was assessed according to the technique described by Dziados et al. [\u003cspan class=\"CitationRef\"\u003e14\u003c/span\u003e]: the first line was drawn from the external to the internal os of the cervix, and the second line was drawn tangentially to the anterior wall of the lower uterine segment, passing through the internal cervical os. Three UCA measurements were obtained, and the greatest value was used for analysis (Fig. 1b).\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec7\" class=\"Section2\"\u003e\n \u003ch2\u003eOutcome measures\u003c/h2\u003e\n \u003cp\u003eThe main outcome of this study was preterm birth before 37 weeks gestation.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec8\" class=\"Section2\"\u003e\n \u003ch2\u003eEthical considerations\u003c/h2\u003e\n \u003cp\u003eThe study was approved by the Ethical Council in Biomedical Research of Hue University of Medicine and Pharmacy, Vietnam (Ethics Committee ID number H2020/035) and the Scientific Council of Haiphong Hospital of Obstetrics and Gynecology, Vietnam (IEC, 1186/QD-BVPSHP). All the participants were fully informed about the study, and written informed consent was obtained before any procedures were conducted.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec9\" class=\"Section2\"\u003e\n \u003ch2\u003eStatistical analysis\u003c/h2\u003e\n \u003cp\u003eSPSS version 20.0 was used for the statistical analysis.\u003c/p\u003e\n \u003cp\u003eThe categorical variables are reported as numbers and percentages, and the continuous variables are reported as the mean and standard deviation. The Kolmogorov‒Smirnov test was used to determine the distribution of the data. The chi-square test was used to compare the distribution of categorical data, and Student\u0026rsquo;s t test or the Mann‒Whitney U test was used to test the difference between two means.\u003c/p\u003e\n \u003cp\u003eThe correlations between the UCA and CL values and gestational age at delivery were evaluated with the Pearson chi-square correlation coefficient. Receiver operating characteristic (ROC) curves were used to assess the ability of the UCA and CL to predict PTB and determine the appropriate cut-off point to provide maximum sensitivity (Se) and specificity (Sp). Multivariate logistic regression adjusted for UCA, CL, maternal age, and obstetric history was performed to determine the associations of the UCA and CL with preterm birth at the cut-off points.\u003c/p\u003e\n \u003cp\u003eA p value\u0026thinsp;\u0026lt;\u0026thinsp;0.05 was considered to indicate statistical significance.\u003c/p\u003e\n\u003c/div\u003e"},{"header":"Results","content":"\u003cdiv class=\"gridtable\"\u003e\n \u003cdiv align=\"left\" class=\"colspec\"\u003e\u003cbr\u003e\u003c/div\u003e\u0026nbsp;\u003ctable id=\"Tab1\" border=\"1\"\u003e\n \u003ccaption language=\"En\"\u003e\n \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e\n \u003cdiv class=\"CaptionContent\"\u003e\n \u003cp\u003eGeneral characteristics of the study participants (n\u0026thinsp;=\u0026thinsp;1,107).\u003c/p\u003e\n \u003c/div\u003e\n \u003c/caption\u003e\n \u003ccolgroup cols=\"5\"\u003e\u003c/colgroup\u003e\n \u003cthead\u003e\n \u003ctr\u003e\n \u003cth align=\"left\" colspan=\"2\"\u003e\n \u003cp\u003eCharacteristics\u003c/p\u003e\n \u003cp\u003en (%) or median\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eFull-term birth\u003c/p\u003e\n \u003cp\u003e(\u0026ge;\u0026thinsp;37 weeks)\u003c/p\u003e\n \u003cp\u003e(n\u0026thinsp;=\u0026thinsp;1.040)\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003ePreterm birth\u003c/p\u003e\n \u003cp\u003e\u0026lt;\u0026thinsp;37 weeks\u003c/p\u003e\n \u003cp\u003e(n\u0026thinsp;=\u0026thinsp;67)\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003ep value\u003c/p\u003e\n \u003c/th\u003e\n \u003c/tr\u003e\n \u003c/thead\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\" colspan=\"5\"\u003e\n \u003cp\u003e\u003cem\u003eMaternal characteristics\u003c/em\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\" colspan=\"2\"\u003e\n \u003cp\u003eMaternal age (years)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e28.83\u0026thinsp;\u0026plusmn;\u0026thinsp;5.12\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e29.27\u0026thinsp;\u0026plusmn;\u0026thinsp;5.24\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.501\u003csup\u003e*\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\" rowspan=\"2\"\u003e\n \u003cp\u003eObstetric history\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eNulliparous\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e444 (42.7%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e24 (35.8%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" rowspan=\"2\"\u003e\n \u003cp\u003e0.523\u003csup\u003e**\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eMultiparous\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e595 (57.2%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e43 (64.2%)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\" colspan=\"2\"\u003e\n \u003cp\u003eGestational age at TVS (weeks)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e19.96\u0026thinsp;\u0026plusmn;\u0026thinsp;2.42\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e21.20\u0026thinsp;\u0026plusmn;\u0026thinsp;1.90\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u0026lt;\u0026thinsp;0.001\u003csup\u003e*\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\" colspan=\"2\"\u003e\n \u003cp\u003eCL at TVS (mm)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e36.35\u0026thinsp;\u0026plusmn;\u0026thinsp;5.07\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e32.06\u0026thinsp;\u0026plusmn;\u0026thinsp;4.19\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u0026lt;\u0026thinsp;0.001\u003csup\u003e*\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\" colspan=\"2\"\u003e\n \u003cp\u003eUCA at TVS (degrees)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e82.41\u0026thinsp;\u0026plusmn;\u0026thinsp;12.10\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e119.41\u0026thinsp;\u0026plusmn;\u0026thinsp;18.46\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u0026lt;\u0026thinsp;0.001\u003csup\u003e*\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\" colspan=\"5\"\u003e\n \u003cp\u003e\u003cem\u003eNeonatal characteristics and outcomes\u003c/em\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\" colspan=\"2\"\u003e\n \u003cp\u003eGestational age at birth (weeks)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e38.74\u0026thinsp;\u0026plusmn;\u0026thinsp;0.87\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e34.93\u0026thinsp;\u0026plusmn;\u0026thinsp;1.68\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u0026lt;\u0026thinsp;0.001\u003csup\u003e*\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\" colspan=\"2\"\u003e\n \u003cp\u003eBirth weight (grams)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e3178.13\u0026thinsp;\u0026plusmn;\u0026thinsp;284.47\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e2446.27\u0026thinsp;\u0026plusmn;\u0026thinsp;404.64\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u0026lt;\u0026thinsp;0.001\u003csup\u003e*\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\" colspan=\"2\"\u003e\n \u003cp\u003eC-section delivery\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e429 (41.3%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e11 (16.4%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u0026lt;\u0026thinsp;0.001\u003csup\u003e**\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\" colspan=\"2\"\u003e\n \u003cp\u003eNICU admission\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e31 (3.0%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e35 (52.2%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u0026lt;\u0026thinsp;0.001\u003csup\u003e**\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\" colspan=\"2\"\u003e\n \u003cp\u003eDeaths\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1 (1.5%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eNA\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003c/table\u003e\n\u003c/div\u003e\n\u003cp\u003e\u003cem\u003e*Student\u0026rsquo;s t test, **chi-square test. SD: standard deviation; TVS: transvaginal ultrasound; CL: cervical length; UCA: uterocervical angle; NICU: neonatal intensive care unit; NA: not applicable.\u003c/em\u003e\u003c/p\u003e\n\u003cp\u003eAmong the 1,107 participants at low risk for preterm birth included in our study, 67 had spontaneous PTB at \u0026lt;\u0026thinsp;37 weeks (6.05%).\u003c/p\u003e\n\u003cp\u003eThe mean UCA at ultrasound was significantly greater in the preterm birth group (119.41\u0026thinsp;\u0026plusmn;\u0026thinsp;18.46 degrees) than in the term group (82.41\u0026thinsp;\u0026plusmn;\u0026thinsp;12.10 degrees) (p\u0026thinsp;\u0026lt;\u0026thinsp;0.001). In addition, the mean CL was significantly shorter in pregnant women in the preterm group (32.06\u0026thinsp;\u0026plusmn;\u0026thinsp;4.19 mm) than in those in the term group (36.35\u0026thinsp;\u0026plusmn;\u0026thinsp;5.07 mm) (p\u0026thinsp;\u0026lt;\u0026thinsp;0.001).\u003c/p\u003e\n\u003cp\u003eThe areas under the curve (AUCs) of the UCA and CL were 0.899 (95% CI: 0.872\u0026ndash;0.926) and 0.240 (95% CI: 0.176\u0026ndash;0.304), respectively (Fig. \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003e).\u003c/p\u003e\n\u003cp\u003eThere was a significant positive correlation between CL and gestational age at delivery (r\u0026thinsp;=\u0026thinsp;0.159, p\u0026thinsp;\u0026lt;\u0026thinsp;0.001) and a significant negative correlation between the UCA and gestational age at delivery (r = -0.396, p\u0026thinsp;\u0026lt;\u0026thinsp;0.001) (Fig. \u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003e).\u003c/p\u003e\n\u003cdiv class=\"gridtable\"\u003e\u0026nbsp;\u003ctable id=\"Tab2\" border=\"1\"\u003e\n \u003ccaption language=\"En\"\u003e\n \u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e\n \u003cdiv class=\"CaptionContent\"\u003e\n \u003cp\u003eThe association among the UCA, CL, and preterm birth at \u0026lt;\u0026thinsp;37 weeks at the UCA and CL cut-off points.\u003c/p\u003e\n \u003c/div\u003e\n \u003c/caption\u003e\n \u003ccolgroup cols=\"5\"\u003e\u003c/colgroup\u003e\n \u003cthead\u003e\n \u003ctr\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eParameter\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003ebeta\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eOR\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003e95% CI\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003ep\u003c/p\u003e\n \u003c/th\u003e\n \u003c/tr\u003e\n \u003c/thead\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eUCA\u0026thinsp;\u0026ge;\u0026thinsp;98.96\u003csup\u003e\u0026deg; a\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e3.571\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e35.56\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e14.88\u0026ndash;84.96\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u0026lt;\u0026thinsp;0.001\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eCL\u0026thinsp;\u0026le;\u0026thinsp;33.8 mm \u003csup\u003eb\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e2.626\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e13.82\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e6.52\u0026ndash;29.29\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u0026lt;\u0026thinsp;0.001\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eUCA\u0026thinsp;\u0026ge;\u0026thinsp;98.96\u003csup\u003e\u0026deg;\u003c/sup\u003e and CL\u0026thinsp;\u0026le;\u0026thinsp;33.8 mm \u003csup\u003ec\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e3.190\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e24.28\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e13.90-42.41\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u0026lt;\u0026thinsp;0.001\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003ctfoot\u003e\n \u003ctr\u003e\n \u003ctd colspan=\"5\"\u003e\u003csup\u003e\u003cem\u003ea\u003c/em\u003e\u003c/sup\u003e\u003cem\u003eadjusted for CL, maternal age, and obstetric history\u003c/em\u003e\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd colspan=\"5\"\u003e\u003csup\u003e\u003cem\u003eb\u003c/em\u003e\u003c/sup\u003e\u003cem\u003eadjusted for UCA, maternal age, and obstetric history\u003c/em\u003e\u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tfoot\u003e\n \u003c/table\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec11\" class=\"Section2\"\u003e\n \u003ch2\u003eAdjusted for maternal age and obstetric history\u003c/h2\u003e\n \u003cp\u003eLogistic regression analysis revealed that a UCA\u0026thinsp;\u0026ge;\u0026thinsp;98.96\u003csup\u003e\u0026deg;\u003c/sup\u003e, a CL\u0026thinsp;\u0026le;\u0026thinsp;33.8 mm, and the combination of a UCA\u0026thinsp;\u0026ge;\u0026thinsp;98.96\u003csup\u003e\u0026deg;\u003c/sup\u003e and a CL\u0026thinsp;\u0026le;\u0026thinsp;33.8 mm were significantly associated with preterm birth at \u0026lt;\u0026thinsp;37 weeks, with ORs (95% CIs) of 35.56 (14.88\u0026ndash;84.96), 13.82 (6.52\u0026ndash;29.29), and 24.28 (13.90-42.41), respectively (Table \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e).\u003c/p\u003e\n \u003cdiv class=\"gridtable\"\u003e\u0026nbsp;\u003ctable id=\"Tab3\" border=\"1\"\u003e\n \u003ccaption language=\"En\"\u003e\n \u003cdiv class=\"CaptionNumber\"\u003eTable 3\u003c/div\u003e\n \u003cdiv class=\"CaptionContent\"\u003e\n \u003cp\u003eDiagnostic performance of the UCA and CL for predicting preterm birth at \u0026lt;\u0026thinsp;37 weeks at the UCA and CL cut-off points.\u003c/p\u003e\n \u003c/div\u003e\n \u003c/caption\u003e\n \u003ccolgroup cols=\"8\"\u003e\u003c/colgroup\u003e\n \u003cthead\u003e\n \u003ctr\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eParameter\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eSe\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eSp\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003ePPV\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eNPV\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eLR+\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eLR-\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eACC\u003c/p\u003e\n \u003c/th\u003e\n \u003c/tr\u003e\n \u003c/thead\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eUCA\u0026thinsp;\u0026ge;\u0026thinsp;98.96\u003csup\u003e\u0026deg;\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.91\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.75\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.193\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.99\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e3.71\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.12\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.76\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eCL\u0026thinsp;\u0026le;\u0026thinsp;33.8 mm\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.25\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.66\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.046\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.93\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.75\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1.13\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.63\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eUCA\u0026thinsp;\u0026ge;\u0026thinsp;98.96\u003csup\u003e\u0026deg;\u003c/sup\u003e and CL\u0026thinsp;\u0026le;\u0026thinsp;33.8 mm\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.66\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.93\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.36\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.98\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e8.87\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.37\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.91\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003c/table\u003e\n \u003c/div\u003e\n \u003cp\u003eThe optimal UCA cut-off for predicting preterm birth at \u0026lt;\u0026thinsp;37 weeks according to the ROC curve was 98.96\u003csup\u003e\u0026deg;\u003c/sup\u003e, with a sensitivity (Se) and specificity (Sp) of 91% and 75.5%, respectively. In addition, at a cut-off point of 33.8 mm, the Se and Sp of the CL for predicting preterm birth at \u0026lt;\u0026thinsp;37 weeks were 25% and 66%, respectively. Moreover, the use of both a UCA\u0026thinsp;\u0026ge;\u0026thinsp;98.96\u003csup\u003e\u0026deg;\u003c/sup\u003e and CL\u0026thinsp;\u0026le;\u0026thinsp;33.8 mm increased the positive predictive value (PPV), positive likelihood ratio (LR+), and accuracy (ACC) for the prediction of preterm birth at \u0026lt;\u0026thinsp;37 weeks to 36%, 8.87, and 91%, respectively (Table \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003e).\u003c/p\u003e\n\u003c/div\u003e"},{"header":"Discussion","content":"\u003cp\u003eAmong the 1,107 low-risk participants included in our study, 6.05% gave birth at \u0026lt;\u0026thinsp;37 weeks, which is lower than that reported in previous studies [\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e, \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eAs shown in Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e, the mean CL was significantly shorter in the participants who delivered preterm than in those who delivered at term, and the mean UCA was significantly greater in those who delivered preterm. These results were in agreement with the findings of previous studies conducted in unselected singleton pregnant women; the UCA was significantly wider in singleton pregnant women with spontaneous PTB [\u003cspan additionalcitationids=\"CR22 CR23 CR24\" citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e]. The combination of pressure applied by the surrounding pelvic organs, more importantly from the growing uterus during pregnancy, could result in the alteration of the internal ostium (os) and cervical function [\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e]. Some ultrasonographic parameters, such as the CL and UCA, have been used to assess cervical structure. In this regard, it can be said that an obtuse cervical angle is associated with a straight and direct force from the pregnant uterus, while an acute cervical angle is associated with a less direct force, maintaining the integrity of the cervix. In other words, the hypothesis is that the cervical angle acts as a barrier that affects the progression of labour when the angle is acute [\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e, \u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e, \u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eOur study revealed that the optimal UCA and CL cut-off values for predicting PTB at \u0026lt;\u0026thinsp;37 gestational weeks in low-risk participants were 98.96 degrees and 33.8 mm, respectively, which were similar to the results reported by Minoo Movahedi et al. [\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e], who recruited patients using the same criteria. In their study, the UCA and CL thresholds for PTB prediction were found to be 106\u0026deg; and 33 mm, respectively. These results were also consistent with the recent study by M Zhang et al. [\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e] on 275 singleton pregnancies in early and mid-pregnancy, that showed the optimal threshold of UCA and CL to predict PTB\u0026thinsp;\u0026lt;\u0026thinsp;37 weeks gestation was 96\u0026deg; and 33.8 mm, respectively. Additionally, Sawaddisan et al. [\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e] reported that a UCA\u0026thinsp;\u0026ge;\u0026thinsp;110\u0026deg; measured later than 19.5 weeks of gestation corresponded to an 83.3% sensitivity for predicting spontaneous PTB. A study conducted by Paul Guerby et al. [\u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e] revealed that a mid-trimester CL\u0026thinsp;\u0026lt;\u0026thinsp;30 mm could detect 35% of all spontaneous PTBs before 35 weeks gestation at a false-positive rate of 5% in low-risk nulliparous women. It is important to note that their study included only women with no previous pregnancies, and ultrasound was conducted between 20 and 24 weeks gestation.\u003c/p\u003e \u003cp\u003eOur findings also demonstrated that at the cut-off points, a UCA\u0026thinsp;\u0026ge;\u0026thinsp;98.96\u0026deg;, a CL\u0026thinsp;\u0026le;\u0026thinsp;33.8 mm, and the combination of a UCA\u0026thinsp;\u0026ge;\u0026thinsp;98.96\u003csup\u003e\u0026deg;\u003c/sup\u003e and a CL\u0026thinsp;\u0026le;\u0026thinsp;33.8 mm were significantly associated with PTB at \u0026lt;\u0026thinsp;37 weeks gestation, with ORs (95% CIs) of 35.56 (14.88\u0026ndash;84.96), 13.82 (6.52\u0026ndash;29.29), and 24.28 (13.90-42.41), respectively.\u003c/p\u003e \u003cp\u003eNonetheless, our study of low-risk pregnant women showed that CL alone did not have a significant impact on predicting PTB, unlike in the general population. A CL of 33.88 mm or less was a poor predictor for PTB, with a low sensitivity of 25%, a specificity of 66%, and an area under the curve (AUC) of only 0.240 (95% CI: 0.176\u0026ndash;0.304). Jeanine van der Ven et al. [\u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e] also reported that mid-trimester CL measurements had limited value for predicting spontaneous PTB in a large population of low-risk singleton pregnant women from 16\u003csup\u003e+\u0026thinsp;0\u003c/sup\u003e-21\u003csup\u003e+\u0026thinsp;6\u003c/sup\u003e weeks gestation, with a poor AUC of 0.56 (95% CI 0.52\u0026ndash;0.6) for PTB before 37 weeks gestation. This finding was consistent with a previous study by Iams et al. [\u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e], which revealed that the positive predictive value of CL was poor (ranging from 6 to 44%), and the sensitivity was only 47% in a low-risk population.\u003c/p\u003e \u003cp\u003eIn contrast, the UCA could be used as a predictive tool to identify women at risk of PTB in this low-risk population. The UCA alone had greater sensitivity and specificity than the CL, with a UCA of 98.96 degrees or more having a sensitivity and specificity of 91% and 75%, respectively. In addition, the AUC of the UCA was 0.899, which performed well in identifying women at risk of PTB in our study population. This finding contradicts the results reported by Sawaddisan et al. [\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e], who reported that the UCA in the second trimester is not a good predictor of PTB in low-risk pregnant women. The discrepancy in the findings may arise from the smaller sample size examined in their study compared to that in our study. In a recent systematic review, Goldstein et al. [\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e] analysed 15 studies that provided data on the test characteristics of the UCA and CL for predicting PTB. The review revealed that for the general population, the UCA alone had a significantly greater sensitivity (0.70; 95% CI: 0.66\u0026ndash;0.73) than CL (0.46; 95% CI: 0.42\u0026ndash;0.49). However, the UCA also had a significantly lower specificity (0.67; 95% CI: 0.66\u0026ndash;0.68) than CL (0.90; 95% CI: 0.89\u0026ndash;0.91) and a lower AUC (0.77) than CL (0.82).\u003c/p\u003e \u003cp\u003eRemarkably, our findings showed that while CL alone was not a reliable predictor of preterm birth in this low-risk population, combining CL with the UCA improved the predictive value compared to the UCA alone. The use of both a UCA\u0026thinsp;\u0026ge;\u0026thinsp;98.96\u003csup\u003e\u0026deg;\u003c/sup\u003e and a CL\u0026thinsp;\u0026le;\u0026thinsp;33.8 mm increased the positive predictive value (PPV), positive likelihood ratio (LR+), and accuracy (ACC) for the prediction of PTB at \u0026lt;\u0026thinsp;37 weeks gestation to 36%, 8.87, and 91%, respectively, which agreed with the results reported in previous studies [\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e, \u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e]. Measuring the UCA at the same time as the CL for screening PTB according to recommendations (at a gestational age of 16\u0026ndash;24 weeks) is convenient in clinical practice and may increase the effectiveness of PTB prediction when combining these two parameters.\u003c/p\u003e \u003cp\u003eThe main strength of this study is that it is the first study conducted among low-risk singleton pregnant women in Vietnam, with a large sample size that demonstrated the ability of the UCA and CL to predict preterm birth. However, even when multivariate logistic regression was used to assess the associations among the UCA, CL, and preterm birth, we cannot deny that other factors may have influenced the outcome of preterm birth, such as smoking status and type of conception. Further multicentre studies are required to evaluate the consistency of these results and establish definitive conclusions.\u003c/p\u003e"},{"header":"Conclusion","content":"\u003cp\u003eThe results of this study suggest that, compared with cervical length alone, the uterocervical angle measured during the second trimester via transvaginal ultrasound could be a valuable parameter for predicting preterm birth in low-risk singleton pregnant women. The use of the combination of the uterocervical angle and cervical length yielded stronger preterm birth prediction values.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eAcknowledgments\u003c/strong\u003e The authors would like to thank all the pregnant women who agreed to participate in this study.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthors contributions\u003c/strong\u003e N.T.H.T., V.V.T., and N.V.Q.H. designed the study. N.T.H.T. and V.V.T. performed data collection. N.T.H.T. and N.V.Q.H. performed statistical analyses and wrote the first manuscript. N.T.H.T., V.V.T., and N.V.Q.H. critically revised successive drafts of the paper. All authors read and approved the final manuscript.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFunding\u003c/strong\u003e This research did not receive specific grants from funding agencies in the public, commercial, or nonprofit sectors.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eData Availability\u003c/strong\u003e The dataset used and/or analyzed during the current study are available from the corresponding author upon reasonable request.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConflict of interest\u003c/strong\u003e The authors declare that they have no conflict of interest.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eEthical approval\u003c/strong\u003e The research proposal was approved by the Ethical Council in Biomedical Research of Hue University of Medicine and Pharmacy, Vietnam (Ethics Committee ID number H2020/035) and the Scientific Council of Haiphong Hospital of Obstetrics and Gynecology, Vietnam (IEC, 1186/QĐ-BVPSHP).\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eInformed consent\u003c/strong\u003e Informed consent was obtained from all individual participants included in the study.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eWHO. \u003cem\u003e152 million babies born preterm in the last decade\u003c/em\u003e. 09-05-2023 Available from: https://www.who.int/news/item/09-05-2023-152-million-babies-born-preterm-in-the-last-decade?s=03.\u003c/li\u003e\n\u003cli\u003eOECD, \u003cem\u003ePreterm birth and low birthweight\u003c/em\u003e. 2014.\u003c/li\u003e\n\u003cli\u003eHarrison, M.S. and R.L. 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McCabe, and S. Socrate, \u003cem\u003eUsing imaging\u003c/em\u003e\u003cem\u003e‐\u003c/em\u003e\u003cem\u003ebased, three\u003c/em\u003e\u003cem\u003e‐\u003c/em\u003e\u003cem\u003edimensional models of the cervix and uterus for studies of cervical changes during pregnancy.\u003c/em\u003e Clinical Anatomy, 2013. \u003cstrong\u003e26\u003c/strong\u003e(1): p. 97-104.\u003c/li\u003e\n\u003cli\u003eKeepanasseril, A., et al., \u003cem\u003ePre\u003c/em\u003e\u003cem\u003e‐\u003c/em\u003e\u003cem\u003einduction sonographic assessment of the cervix in the prediction of successful induction of labour in nulliparous women.\u003c/em\u003e Australian and New Zealand journal of obstetrics and gynaecology, 2007. \u003cstrong\u003e47\u003c/strong\u003e(5): p. 389-393.\u003c/li\u003e\n\u003cli\u003eWeiner, E., et al., \u003cem\u003eThe placental factor in spontaneous preterm birth in twin vs. singleton pregnancies.\u003c/em\u003e European Journal of Obstetrics \u0026amp; Gynecology and Reproductive Biology, 2017. \u003cstrong\u003e214\u003c/strong\u003e: p. 1-5.\u003c/li\u003e\n\u003cli\u003eMovahedi, M., et al., \u003cem\u003eThe uterocervical angle-cervical length ratio: A promising predictor of preterm birth?\u003c/em\u003e International Journal of Gynecology \u0026amp; Obstetrics. \u003cstrong\u003en/a\u003c/strong\u003e(n/a).\u003c/li\u003e\n\u003cli\u003eZhang, M., et al., \u003cem\u003eChanges of uterocervical angle and cervical length in early and mid-pregnancy and their value in predicting spontaneous preterm birth.\u003c/em\u003e Frontiers in Physiology, 2024. \u003cstrong\u003e15\u003c/strong\u003e.\u003c/li\u003e\n\u003cli\u003eGuerby, P., et al., \u003cem\u003eMidtrimester Cervical Length in Low-Risk Nulliparous Women for the Prediction of Spontaneous Preterm Birth: Should We Consider a New Definition of Short Cervix?\u003c/em\u003e Am J Perinatol, 2023. \u003cstrong\u003e40\u003c/strong\u003e(2): p. 187-193.\u003c/li\u003e\n\u003cli\u003evan der Ven, J., et al., \u003cem\u003eThe capacity of mid-pregnancy cervical length to predict preterm birth in low-risk women: a national cohort study.\u003c/em\u003e Acta Obstetricia et Gynecologica Scandinavica, 2015. \u003cstrong\u003e94\u003c/strong\u003e(11): p. 1223-1234.\u003c/li\u003e\n\u003cli\u003eIams, J.D., et al., \u003cem\u003eThe Length of the Cervix and the Risk of Spontaneous Premature Delivery.\u003c/em\u003e New England Journal of Medicine, 1996. \u003cstrong\u003e334\u003c/strong\u003e(9): p. 567-573.\u003c/li\u003e\n\u003cli\u003eKnight, J.C., et al., \u003cem\u003eUterocervical Angle Measurement Improves Prediction of Preterm Birth in Twin Gestation.\u003c/em\u003e Am J Perinatol, 2018. \u003cstrong\u003e35\u003c/strong\u003e(7): p. 648-654.\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"archives-of-gynecology-and-obstetrics","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"arch","sideBox":"Learn more about [Archives of Gynecology and Obstetrics](https://www.springer.com/journal/404)","snPcode":"","submissionUrl":"https://www.editorialmanager.com/arch/default.aspx","title":"Archives of Gynecology and Obstetrics","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"Uterocervical angle, Cervical length, Preterm birth, Low risk, Singleton pregnancy","lastPublishedDoi":"10.21203/rs.3.rs-4184828/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-4184828/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003e \u003cb\u003ePurpose\u003c/b\u003e Preterm birth is the leading cause of early neonatal morbidity and mortality. Strategies to predict preterm birth risk can help improve pregnancy outcomes. Even pregnant women without known risk factors for preterm birth can also experience it. This study aimed to evaluate the ability of the uterocervical angle and cervical length to predict preterm birth in low-risk singleton pregnant women.\u003c/p\u003e \u003cp\u003e \u003cb\u003eMethods\u003c/b\u003e A prospective study of 1,107 singleton pregnant women between 16\u003csup\u003e+\u0026thinsp;0\u003c/sup\u003e and 23\u003csup\u003e+\u0026thinsp;6\u003c/sup\u003e weeks gestation at low risk for preterm birth who were treated at the Haiphong Hospital of Obstetrics and Gynecology, Vietnam, between September 2020 and September 2021 was conducted. A single sonographer assessed the cervical length and the uterocervical angle using transvaginal ultrasonography. The patients were followed up until delivery to determine the main pregnancy outcome (preterm birth before 37 weeks gestation). The cut-off points for the uterocervical angle and cervical length were established by analysing the receiver operating characteristic curve. The sensitivity, specificity, likelihood ratio, and positive and negative predictive values of the uterocervical angle and cervical length for predicting preterm birth were determined.\u003c/p\u003e \u003cp\u003e \u003cb\u003eResults\u003c/b\u003e A uterocervical angle\u0026thinsp;\u0026ge;\u0026thinsp;98.86\u0026deg; predicted preterm birth at \u0026lt;\u0026thinsp;37 weeks, with a sensitivity and specificity of 91% and 75.5%, respectively. A cervical length\u0026thinsp;\u0026le;\u0026thinsp;33.8 mm predicted preterm birth at \u0026lt;\u0026thinsp;37 weeks with a sensitivity and specificity of 25% and 66%, respectively. A uterocervical angle\u0026thinsp;\u0026ge;\u0026thinsp;98.96\u003csup\u003e\u0026deg;\u003c/sup\u003e combined with a cervical length\u0026thinsp;\u0026le;\u0026thinsp;33.8 mm increased the positive predictive value, positive likelihood ratio, and accuracy of preterm birth prediction to 36%, 8.87, and 91%, respectively.\u003c/p\u003e \u003cp\u003e \u003cb\u003eConclusion\u003c/b\u003e Compared to the cervical length, the uterocervical angle can be considered a valuable ultrasound parameter for predicting preterm birth in low-risk singleton pregnant women. Combining both the uterocervical angle and cervical length yielded stronger preterm birth prediction values.\u003c/p\u003e","manuscriptTitle":"Uterocervical angle and cervical length measurements for preterm birth prediction in low-risk singleton pregnant women: A prospective cohort study","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2024-04-05 16:39:28","doi":"10.21203/rs.3.rs-4184828/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"reviewerAgreed","content":"","date":"2024-04-09T07:43:19+00:00","index":0,"fulltext":""},{"type":"reviewersInvited","content":"","date":"2024-04-01T09:57:07+00:00","index":"","fulltext":""},{"type":"editorInvited","content":"Archives of Gynecology and Obstetrics","date":"2024-03-29T10:46:58+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2024-03-29T06:59:39+00:00","index":"","fulltext":""},{"type":"submitted","content":"Archives of Gynecology and Obstetrics","date":"2024-03-28T20:27:29+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"archives-of-gynecology-and-obstetrics","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"arch","sideBox":"Learn more about [Archives of Gynecology and Obstetrics](https://www.springer.com/journal/404)","snPcode":"","submissionUrl":"https://www.editorialmanager.com/arch/default.aspx","title":"Archives of Gynecology and Obstetrics","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"be707f1e-45dd-430e-a9b9-242810b64d7c","owner":[],"postedDate":"April 5th, 2024","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[],"tags":[],"updatedAt":"2024-08-01T16:15:48+00:00","versionOfRecord":{"articleIdentity":"rs-4184828","link":"https://doi.org/10.1007/s00404-024-07646-4","journal":{"identity":"archives-of-gynecology-and-obstetrics","isVorOnly":false,"title":"Archives of Gynecology and Obstetrics"},"publishedOn":"2024-07-17 16:05:05","publishedOnDateReadable":"July 17th, 2024"},"versionCreatedAt":"2024-04-05 16:39:28","video":"","vorDoi":"10.1007/s00404-024-07646-4","vorDoiUrl":"https://doi.org/10.1007/s00404-024-07646-4","workflowStages":[]},"version":"v1","identity":"rs-4184828","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-4184828","identity":"rs-4184828","version":["v1"]},"buildId":"zQwnuV7TCBrMSSSToR1PI","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}