Transvaginal ultrasonography of the uterine cervix in hospitalized women with preterm labor

Cervical assessment

Transvaginal scan (TVS) of cervical length (CxL) at mid-trimester anomaly scan in asymptomatic pregnancy is useful for predicting the risk of preterm birth. In symptomatic women, measurement of CxL at presentation can help to distinguish between true and false preterm labor (PTL), and who might not deliver within 48 h and seven days. In both groups, the individualization of risk would lead to improvement of antenatal care, including frequency of visits, patient education to identify earlier symptoms, avoid excessive hospitalization, and unnecessary steroids. It is also possible that vaginal progesterone and/or cerclage reduce the PTB risk on those asymptomatic women with short cervix. The aim is to review the evidence that supports the use of TVS of CxL in both asymptomatic and symptomatic pregnant women for the prediction and management of PTL.

Comparison of Four Tests for Preterm Birth Prediction in Symptomatic Singleton Women: A Prospective Cohort Study

Background and Purpose: It is challenging to predict preterm births accurately. We sought to compare the diagnostic performance of cervical length in predicting preterm birth to those of contraction recording in cardiotocography (CTG), cervical funneling, and Bishop score. Methods: A total of 371 women with singleton pregnancies and threatened preterm labor admitted to tertiary hospitals of northwestern Iran were included in this prospective cohort study and followed up until childbirth. Transvaginal ultrasound was utilized to assess the cervical length and funneling. Also, a CTG test and digital vaginal examination were performed. The data of 218 women were analyzed in the STATA software. The sensitivity and other diagnostic performances, and 95% confidence intervals, were reported. Results: The CTG uterine contraction recording had the highest sensitivity for predicting birth within the next 2 days, whereas a Bishop score ≥6 revealed the highest specificity, positive predictive value, and positive likelihood ratio. Inadequate cervical length for gestational age exhibited a high negative predictive value and the lowest negative likelihood ratio. Conclusion: The cervical length test has good diagnostic and prognostic performance among the four tests for preterm birth. Cervical funneling and CTG tests have poor predictive value, whereas the Bishop score has a superior diagnostic performance to the other tests.

Development and validation of a prediction model on spontaneous preterm birth in twin pregnancy: a retrospective cohort study

BACKGROUND

This study was conducted to develop and validate an individualized prediction model for spontaneous preterm birth (sPTB) in twin pregnancies.

METHODS

This a retrospective cohort study included 3845 patients who gave birth at the Chongqing Maternal and Child Health Hospital from January 2017 to December 2022. Both univariable and multivariable logistic regression analyses were performed to find factors associated with sPTB. The associations were estimated using the odds ratio (OR) and the 95% confidence interval (CI). Model performance was estimated using sensitivity, specificity, accuracy, area under the receiver operating characteristic curve (AUC) and decision curve analysis (DCA).

RESULTS

A total of 1313 and 564 cases were included in the training and testing sets, respectively. In the training set, univariate and multivariate logistic regression analysis indicated that age ≥ 35 years (OR, 2.28; 95% CI 1.67-3.13), pre-pregnancy underweight (OR, 2.36; 95% CI 1.60-3.47), pre-pregnancy overweight (OR, 1.67; 95% CI 1.09-2.56), and obesity (OR, 10.45; 95% CI, 3.91-27.87), nulliparity (OR, 0.58; 95% CI 0.41-0.82), pre-pregnancy diabetes (OR, 5.81; 95% CI 3.24-10.39), pre-pregnancy hypertension (OR, 2.79; 95% CI 1.44-5.41), and cervical incompetence (OR, 5.12; 95% CI 3.08-8.48) are independent risk factors for sPTB in twin pregnancies. The AUC of the training and validation set was 0.71 (95% CI 0.68-0.74) and 0.68 (95% CI 0.64-0.73), respectively. And then we integrated those risk factors to construct the nomogram.

CONCLUSIONS

The nomogram developed for predicting the risk of sPTB in pregnant women with twins demonstrated good performance. The prediction nomogram serves as a practical tool by including all necessary predictors that are readily accessible to practitioners.

Measurement of the uterocervical angle for the prediction of preterm birth in symptomatic women

Purpose

To examine if the uterocervical angle (UCA) can be used to predict preterm delivery in women with painful and regular uterine contractions and a cervical length of 25 mm or less.

Methods

Retrospective study at the perinatal unit of the University Hospital of Tuebingen, Germany. Women with singleton gestation and preterm contractions between 24 + 0 and 33 + 6 weeks’ gestation were included. For the UCA measurement, a line is placed from the internal os to the external os irrespective of whether the cervix is straight or curved. A second line is drawn to delineate the lower uterine segment. The angle between the two lines is the UCA measurement. The measurements were taken on stored images from our database.

Results

The study consisted of 213 singleton pregnancies. At the time of UCA measurement, median maternal and gestational age was 31.4 years and 29.7 weeks’ gestation. Median gestational age at delivery was 35.3 weeks and the corresponding birth weight 2480 g, respectively. The UCA measurement in women who delivered within 2 days, between 3–7 days and after 7 days was not helpful to distinguish between these three groups [median UCA measurements: 108.5°, 108.0° and 107.3° (Kruskal–Wallis test p = 0.576)]. Uni- and multivariate logistic multiple regression analysis demonstrated that the delivery within 2 days was only dependent on the gestational age and the cervical length at the time of presentation.

Conclusion

The measurement of UCA is not useful in predicting preterm birth in the subsequent 7 days after an episode of preterm contractions.

The prediction of preterm delivery: What is new?

Preterm birth, defined as birth occurring prior to 37 weeks gestation, is a serious obstetric problem accounting for 11% of pregnancies worldwide. It is associated with significant neonatal morbidity and mortality. Predictive tests for preterm birth are incredibly important, given the huge personal, economic, and health impacts of preterm birth. They can provide reassurance for women who are unlikely to deliver early, but they are also important for highlighting those women at higher risk of premature delivery so that we can offer prophylactic interventions and help guide antenatal management decisions. Unfortunately, there is unlikely to be a single test for predicting preterm birth, but a combination of tests is likely to improve clinical prediction. This review explores the clinical utility of the currently marketed predictive tests for preterm birth in both singleton and multiple pregnancies, as well as discussing novel predictive tests that may be useful in the future.

Predictors of preterm birth

Cervical length (CL) measured by transvaginal ultrasound examination (TVUE) best identifies the risk for preterm birth (PTB). It identifies women at risk who can benefit from corticosteroids or in utero transfer. Early screening improves effectiveness of tocolysis. It reduces iatrogenicity and cost. In preterm premature rupture of membranes (PPROM), CL is devoid of infectious risk and predicts duration of the latency phase but not the risk of perinatal sepsis. Asymptomatic women at risk should be screened at a 2-week interval starting from 16 to 18 weeks, up to 24 weeks. CLs <10th centile are at risk of PTB, especially with decrease in CL after 16 weeks. Repeat ultrasound improves predictive values. Stable CL calls for term delivery. Funneling does not improve predictivity of CL. In twin pregnancies, CL reduces unnecessary interventions. In symptomatic women, fetal fibronectin performs less than CL. Its combination with inconclusive CL has not emerged productive through randomized controlled trials (RCTs), and studies with homogeneous management for preterm labor (PTL) suggest that up to 15% of unjustified hospitalizations and treatment could be avoided.

Multiple gestations and preterm birth

Preterm birth is a major concern in modern obstetrics, and an important source of morbidity and mortality in newborns. Among twin pregnancies, especially, preterm birth is highly prevalent, and it accounts for almost 50% of the complications observed in this obstetrical population. In this article, we review the existing literature regarding the prediction and prevention of preterm birth in both symptomatic and asymptomatic twin pregnancies. In asymptomatic twin pregnancies, the best two predictive tests were cervical length (CL) measurement and cervicovaginal fetal fibronectin (fFN) testing. A single measurement of transvaginal CL at 20-24 weeks of gestation <20 mm or <25 mm is a good predictor of spontaneous preterm birth at <28, <32, and <34 weeks of gestation. A CL beyond 25 mm is associated with a 2% risk for birth before 28 weeks and with a 65% chance for a term pregnancy. Cervicovaginal fFN may be slightly less accurate than CL; however, it has a high negative predictive value in women presenting with threatened preterm labor, as <2% of these women will deliver within one week if the fFN is negative. In symptomatic twin pregnancies, no tests have proven accurate in predicting the risk of preterm birth. For the prevention of preterm birth in asymptomatic twins, regardless of CL, no treatment including bed rest, limitation of home activities, prophylactic tocolysis, progesterone, or cerclage has been shown to reduce the rate of preterm birth. Cervical pessaries might be of interest in cases where there is a short cervix (<25 mm and <38 mm, respectively) but these results need to confirmed in future trials.

Prediction of preterm birth in twin gestations using biophysical and biochemical tests

The objective of this study was to determine the performance of biophysical and biochemical tests for the prediction of preterm birth in both asymptomatic and symptomatic women with twin gestations. We identified a total of 19 tests proposed to predict preterm birth, mainly in asymptomatic women. In these women, a single measurement of cervical length with transvaginal ultrasound before 25 weeks of gestation appears to be a good test to predict preterm birth. Its clinical potential is enhanced by the evidence that vaginal progesterone administration in asymptomatic women with twin gestations and a short cervix reduces neonatal morbidity and mortality associated with spontaneous preterm delivery. Other tests proposed for the early identification of asymptomatic women at increased risk of preterm birth showed minimal to moderate predictive accuracy. None of the tests evaluated in this review meet the criteria to be considered clinically useful to predict preterm birth among patients with an episode of preterm labor. However, a negative cervicovaginal fetal fibronectin test could be useful in identifying women who are not at risk for delivering within the next week, which could avoid unnecessary hospitalization and treatment. This review underscores the need to develop accurate tests for predicting preterm birth in twin gestations. Moreover, the use of interventions in these patients based on test results should be associated with the improvement of perinatal outcomes.

Short and inflamed cervix predicts spontaneous preterm birth (COLIBRI study)

OBJECTIVE

To develop a new strategy of predicting spontaneous preterm birth (sPTB) by combination of transvaginal ultrasound (TVUS) assessment and inflammatory proteins detection in vaginal secretions.

METHODS

Prospective study of 87 women referred for cervical length assessment with a standardized TVUS combined to vaginal secretions sampling. Samples were analyzed for presence of 10 cytokines. Main outcome was sPTB (<37 weeks of gestation). Associations were assessed with the chi-square, Fisher's exact test (p < 0.05) and Wald's logistic regression.

RESULTS

sPTB occurred in 25.3% of women at a median gestational age of 35.6 weeks of gestation. Short cervix (<25 mm) (n = 24) was associated with sPTB (p < 0.01) as interleukine (IL)-1β, IL-8 and IL-10 in vaginal secretions (p < 0.05). In multivariate analysis, short cervix and IL-8 in vaginal secretions were independently associated with sPTB (OR 3.58 (95%CI 1.02; 12.61) and 14.55 (95%CI 1.64; 128.83), respectively) as their combination (OR 4.33 (95%CI 1.25; 14.95)). By categorizing cervical length by presence of IL-8, sPTB occurred in 55.6% of women with a short inflamed cervix.

CONCLUSION

COLIBRI study used a novel, single-step method of vaginal secretions sampling during TVUS and demonstrated that combination of short cervix and IL-8 in vaginal secretions is a promising sPTB predictive test.

[Predictive value of combined fibronectin and ultrasound cervical assessment in twin pregnancies]

OBJECTIVE

To test a sequential test with fetal fibronectin detection after ultrasound measurement of cervical length to predict preterm delivery in twin pregnancies with preterm labor.

PATIENTS AND METHODS

Descriptive retrospective study on 50 women with twin pregnancy hospitalised for preterm labor between 24 and 34 weeks and 6 days of gestation. The primary outcomes were preterm delivery before 34 or 37 weeks of gestation or within 7 or 14 days. Selective use of fibronectin after cervical length measurement has been tested, with a sequential test considered positive if cervical length was less than or equal to 15mm or if cervical length was between 16 and 30mm with fetal fibronectin positive.

RESULTS

The sensitivity/specificity/and positive and negative predictive values of fetal fibronectin positive were 71%, 64%, 26%, et 93% for delivery within 7 days; those of cervical length less than or equal to 20mm were 89%, 51%, 31%, et 95% for delivery before 34 weeks and 6 days. The efficiency of the sequential test seemed better than each test and than for singleton pregnancies keeping an excellent negative predictive value: sensitivity of 75%, specificity of 63%, positive predictive value of 26% and negative predictive value of 93.5% for prediction of preterm delivery within 14 days. The use of this sequential test could have decreased half of fibronectin tests.

DISCUSSION AND CONCLUSION

A sequential test with selective use of fetal fibronectin detection in twin pregnancies selected by ultrasound measurement of cervical length appears to be effective for predicting preterm birth if preterm labor, avoiding half of fibronectin tests.

Additional effects of the cervical length measurement in women with preterm contractions: a systematic review

Purpose

Transvaginal cervical length measurement in women with symptoms of preterm labor has been used to decide if treatment is necessary. Cervical length measurement may also have additional effects on patients, such as providing reassurance, although the evidence to support this is unclear. We explored and summarized to what extent additional effects of cervical length measurement in women with threatened preterm labor have been reported in the clinical literature and what the magnitude of these effects was.

Methods

We performed a systematic review of the literature to identify articles reporting on cervical length measurements in women with symptoms of preterm labor. We assessed whether these articles reported patient outcomes other than preterm delivery.

Results

The electronic and hand search resulted in 764 articles, of which 172 met initial criteria for further eligibility assessment. We found 12 articles that reported additional effects of cervical length measurement in symptomatic women, such as the reassurance or the sensory consequences related to the transvaginal procedure. None of the articles quantified such additional effects.

Conclusions

There appears to be a gap between the presumed effects of cervical length measurement on patient outcomes, such as patients’ reassurance, and the actual assessment of these effects during test evaluations. We suggest that future evaluations of prognostic preterm labor tests include a comprehensive assessment of patient outcomes.

Transvaginal sonographic cervical length for the prediction of spontaneous preterm birth in twin pregnancies: a systematic review and metaanalysis

OBJECTIVE

To assess the accuracy of transvaginal sonographic cervical length (CL) in predicting spontaneous preterm birth in women with twin pregnancies.

STUDY DESIGN

Systematic review and metaanalysis of predictive test accuracy.

RESULTS

Twenty-one studies (16 in asymptomatic women and 5 in symptomatic women) with a total of 3523 women met the inclusion criteria. Among asymptomatic women, a CL

CONCLUSION

Transvaginal sonographic CL at 20-24 weeks' gestation is a good predictor of spontaneous preterm birth in asymptomatic women with twin pregnancies.

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Key Words

• cervical length
• preterm birth
• prediction
• metaanalysis
• systematic review

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MESH Headings

• Cervix Uteri/anatomy & histology
• Cervix Uteri/diagnostic imaging
• Female
• Gestational Age
• Humans
• Incidence
• Infant, Newborn
• Predictive Value of Tests
• Pregnancy
• Pregnancy Outcome
• Pregnancy, Multiple
• Premature Birth/diagnostic imaging
• Premature Birth/epidemiology
• Risk Assessment
• Twins
• Ultrasonography, Prenatal

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Grants

• ZIA HD002401 Intramural NIH HHS

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Affiliation(s)

Agustín Conde-Agudelo Perinatology Research Branch, Eunice Kennedy Shriver National Institute of Child Health and Human Development/National Institutes of Health/Department of Health and Human Services, Bethesda, MD, USA
Roberto Romero
Sonia S Hassan
Lami Yeo

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Collaborators Collapse

Transvaginal cervical length measurement for prediction of preterm birth in women with threatened preterm labor: a meta-analysis

OBJECTIVES

To integrate data on the performance of cervical length measurement for the prediction of preterm birth in symptomatic women.

METHODS

MEDLINE, SCOPUS and manual searches for studies with transvaginal ultrasound measurement of the cervical length in symptomatic women were carried out. Random effects models were used for data integration, and pooled test estimates of sensitivity, specificity, and positive and negative likelihood ratios (LR+ and LR-) were calculated along with their 95% CIs.

RESULTS

Twenty-eight studies fulfilled the selection criteria. For birth within 1 week from presentation, the pooled sensitivity, specificity, LR+ and LR- of cervical length < 15 mm were 59.9% (95% CI, 52.7-66.8%), 90.5% (95% CI, 89.0-91.9%), 5.71 (95% CI, 3.77-8.65) and 0.51 (95% CI, 0.33-0.80), respectively. The same estimates for studies with presentation at or before 34 + 0 weeks were 71.0% (95% CI, 60.6-79.9%), 89.8% (95% CI, 87.4-91.9%), 5.19 (95% CI, 2.29-11.74) and 0.38 (95% CI, 0.11-1.34), respectively. For prediction of birth before 34 weeks, the pooled sensitivity, specificity, LR+ and LR- of cervical length < 15 mm were 46.2% (95% CI, 34.8-57.8%), 93.7% (95% CI, 90.7-96.0%), 4.31 (95% CI, 2.73-6.82) and 0.63 (95% CI, 0.38-1.04), respectively. There was considerable heterogeneity across studies in most estimates.

CONCLUSIONS

Measurement of cervical length in symptomatic women can detect a significant proportion of those who will deliver within 1 week and help to rationalize their management. The considerable heterogeneity across studies may be indicative of methodological flaws, which either were not reported at all or were under-reported.

Prevention of preterm birth based on short cervix: symptomatic women with preterm labor or premature prelabor rupture of membranes

The diagnosis of preterm labor (PTL) is challenging, especially in women whose cervical dilatation is <2 cm and who are <80% effaced. In symptomatic women, with threatened PTL in both singletons and twins, transvaginal ultrasound cervical length (CL) identifies a high-risk group that is more likely to be in true PTL, more likely to deliver sooner, and more likely to deliver preterm. The addition of fetal fibronectin improves the predictive accuracy in women whose CL is <30 mm but >15 mm. Transvaginal ultrasound CL can also be performed in the presence of ruptured membranes and predicts latency. Although additional data are needed, the evidence so far suggests that the use of transvaginal ultrasound CL and fetal fibronectin can be used to better identify and manage women with PTL likely to have an imminent preterm delivery, and to avoid interventions in women who would not.

Prediction of preterm birth: cervical sonography

The cervix has to open to allow vaginal birth. Ultrasound has now shown that this lower part of the uterus begins to show changes weeks before eventual birth. Only transvaginal ultrasound should be used to evaluate the cervix for prediction of preterm birth (PTB). The shortest best cervical length (CL) is the most effective measurement for clinical use. Proper technique is paramount for accurate results. The risk of PTB increases with ever shorter CL (<25 mm). Other factors that must be carefully considered when using CL for prediction of PTB are number of fetuses, risk factors for PTB, and gestational age at screening.

Gestational age at cervical length measurement and incidence of preterm birth

OBJECTIVE

To estimate the risk of spontaneous preterm birth based on transvaginal ultrasound cervical length and gestational age at which cervical length was measured.

METHODS

Women at high risk for spontaneous preterm birth and with transvaginal ultrasound cervical length measurements between weeks 12 and 32 were identified at one institution between July 1995 and June 2005. Inclusion criteria for women at high risk for spontaneous preterm birth were prior spontaneous preterm birth at 14 to 35 weeks, cone biopsy, müllerian anomaly, or two or more dilation and evacuations. Women with multiple gestations, cerclage, indicated preterm birth, or fetal anomalies were excluded. Logistic regression was used to estimate the spontaneous preterm birth risk before 35, 32, and 28 weeks.

RESULTS

Seven hundred five women received 2,601 transvaginal ultrasound measurements for cervical length. The incidences of spontaneous preterm birth before 35, 32, and 28 weeks were 17.7, 10.6, and 6.7%, respectively. The risk of spontaneous preterm birth before 35 weeks decreased by approximately 6% for each additional millimeter of cervical length (odds ratio 0.94, 95% confidence interval, 0.92-0.95, P=.001) and by approximately 5% for each additional week of pregnancy at which the cervical length was measured (odds ratio 0.95, 95% confidence interval 0.92-0.98, P=.004). Similar results were obtained for spontaneous preterm birth before 32 and 28 weeks.

CONCLUSION

Gestational age at which transvaginal ultrasound cervical length is measured significantly affects the calculation of risk of spontaneous preterm birth. The spontaneous preterm birth risk increases as the length of the cervix declines and as the gestational age decreases. These spontaneous preterm birth risks are important for counseling and management for women with various degrees of short cervical length at different gestational ages.

LEVEL OF EVIDENCE

II.

The use of a variable cut-off value of cervical length in women admitted for preterm labor before and after 32 weeks

OBJECTIVE

To determine whether the optimal cut-off value to predict low risk of preterm delivery in women admitted for preterm labor should be adjusted for gestational age.

METHODS

A cohort of 333 women with singleton pregnancies admitted with preterm labor and intact membranes between 24 and < 36 weeks' gestation was studied. The women were categorized according to prematurity into one of two groups: those admitted at < 32 weeks (Group 1, very preterm) and those admitted at >or= 32 weeks (Group 2, preterm). Transvaginal ultrasound was performed 24-48 h after admission and cervical length measured. The predictive value of different cut-off points was explored. Outcome variables were spontaneous preterm delivery within 7 days of admission and delivery at < 34 weeks.

RESULTS

The mean ( +/- SD) gestational ages at admission and delivery were 31.9 ( +/- 2.6) and 37.5 ( +/- 2.2) weeks, respectively, and the mean ( +/- SD) cervical length was 30.4 ( +/- 8.9) mm. The rates of spontaneous delivery within 7 days and at < 34 weeks were 6.3 and 7.0%, respectively. The cut-off value of 15-mm cervical length showed a sensitivity, negative predictive value and false positive rate for delivery within 7 days of 0, 96.5 and 2.7% in the very preterm group, and 35.3, 94.6 and 4% in the preterm group, respectively. For a cut-off point of 25 mm, these values were 75, 99 and 14.3%, and 70.6, 96.8 and 24.5%.

CONCLUSIONS

The predictive value of different cut-off points of cervical length is similar at different gestational ages. However, the higher false positive rate after 32 weeks' gestation might justify the adoption of gestational-age related cut-off values in clinical protocols. In women admitted at < 32 weeks' gestation, a cut-off point of 25 mm may be used to predict a low risk of preterm delivery, whereas in women admitted at 32 weeks or later, 15 mm might be more appropriate. Published by John Wiley & Sons, Ltd.

Cervical length and prediction of preterm delivery

PURPOSE OF REVIEW

To present a summary of the literature and most recent advances in the clinical use of cervical length for the prediction of preterm birth.

RECENT FINDINGS

Cervical length is predictive of preterm birth in all populations studied, including asymptomatic women with prior cone biopsy, mullerian anomalies, or multiple dilation and evacuations. While cervical length remains the most predictive measurement, funneling may add to its predictive value in certain populations. In terms of interventions aimed at preventing preterm birth once a short cervical length has been identified in asymptomatic women, recent data from a meta-analysis of all trials published so far point to the benefit of ultrasound-indicated cerclage in women with both a prior preterm birth and a cervical length less than 25 mm. Other interventions for a short cervical length such as progesterone and indomethacin are promising, but deserve further study before clinical recommendations can be made. In women with symptomatic preterm labor, a recent trial has shown that knowledge of cervical length (and fetal fibronectin) may be beneficial both in terms of time to triage and reduction of preterm birth.

SUMMARY

Transvaginal ultrasound cervical length used as a screening tool for prediction and prevention of preterm birth can significantly improve the health outcomes of pregnant patients and their babies.

Diagnosis of early preterm labour

While preterm contractions occur almost as often extremely preterm as they do closer to term, birth due to spontaneous preterm labour before 27 weeks of gestation is rare, accounting for 0.05-0.7% of all births in different populations. Although the likelihood that uterine contractions before 27 weeks of gestation represent true preterm labour is low, the risk of adverse outcome in such cases is high. A correct diagnosis is important, and a useful diagnostic test should have a high sensitivity. In most reports, only 30-40% of women hospitalised for spontaneous preterm labour experience a preterm birth, suggesting a low positive predictive value of clinical diagnosis based on uterine contractions and vaginal examination. Transvaginal ultrasonographic scanning (TVUSS) of cervical length has shown a high sensitivity for preterm birth, 90-100% for preterm birth before 33-35 weeks, using a liberal cutoff at 30 mm. Assessment of cervicovaginal fetal fibronectin (FFN) levels has shown a sensitivity of about 80%. Adding FFN assessment to TVUSS might contribute insignificantly to the prediction of preterm birth. In a retrospective study of 147 women with spontaneous preterm labour and intact membranes before 27 weeks in our department, 61% of hospitalised women and 77% of women receiving tocolytic infusion therapy delivered before 32 weeks. Among 66 singleton pregnancies delivered before 32 weeks, at admission, 94% either had an effaced cervix or cervix with >/=2 cm dilation (74%), vaginal bleeding (61%) or serum C-reactive protein level >20 mg/l (40%), whereas one of these findings only was present in 18% of women who delivered at later gestations. Among 132 women with symptoms of spontaneous preterm contractions before 27 weeks not admitted for hospital care, only 2 (1.5%) delivered before 32 weeks, not significantly higher than for all other women (0.6%). Although TVUSS may be useful when the diagnosis of spontaneous preterm labour is in doubt, the main predicament in early spontaneous preterm labour may not be to predict preterm birth but to prevent it, since many women appear in advanced labour or with manifest chorioamnionitis.

Dynamic cervical change: is real-time sonographic cervical shortening predictive of preterm delivery in patients with symptoms of preterm labor?

OBJECTIVES

To determine prospectively if dynamic cervical change (spontaneous real-time cervical shortening) is predictive of preterm delivery at < 37 weeks' gestation in patients with symptoms of preterm labor.

METHODS

This was a prospective study of patients at 23-34 weeks' gestation who were symptomatic for preterm labor. Patients underwent a 10-min real-time sonographic cervical length assessment with measurements taken at 1-min intervals. The presence or absence of dynamic cervical change, defined as real-time changes in cervical length observable to the naked eye of the sonologist during the examination, was recorded. Gestational age at delivery was obtained from medical records. Preterm delivery was defined as delivery at < 37 weeks' gestation. Dynamic cervical change and initial and minimum cervical lengths were assessed for prediction of preterm delivery.

RESULTS

Seventy-six patients were enrolled, and 66 were available for outcome analysis. Thirty-one patients (47%) exhibited dynamic cervical change. Patients with dynamic change had shorter initial cervical lengths (27 mm vs. 36 mm, P = 0.001), shorter minimum cervical lengths (20 vs. 33 mm, P < 0.001) and larger changes in cervical length during the examination period (10 vs. 4 mm, P < 0.001). In the subgroup of patients with an initial cervical length > 30 mm, those with dynamic change delivered earlier than did those without dynamic change (36.8 vs. 38.6 weeks, P = 0.02), and a higher percentage delivered preterm (27% vs. 11%, odds ratio (OR), 3.0 (0.5-17.0)). Multivariate analysis showed that minimum cervical length was a better predictor of preterm delivery than was initial cervical length.

CONCLUSIONS

Dynamic cervical change occurs frequently in association with shortened cervical length. In patients with longer initial cervical lengths, dynamic change may increase the risk for preterm delivery. When dynamic change is noted in a patient with preterm labor symptoms, use of the minimum cervical length observed may be better compared with initial cervical length for determining preterm delivery risk.

Cervical Sonography in Women with Symptoms of Preterm Labor

In the last few years, ultrasound of the cervix during pregnancy has been the focus of much research. Significant advances have been made in its technique and in understanding the proper role of this procedure in several clinical settings. This article reviews the evidence for the clinical role of transvaginal cervical assessment in women with symptoms of preterm labor.

[Ultrasonographic measurement of cervical length in twin pregnancies with preterm labor: comparison with singleton pregnancies]

OBJECTIVE

Our purpose was to assess the utility of ultrasonographic measurement of cervical length for predicting preterm delivery in pregnant women with twin pregnancy and preterm labor.

PATIENTS AND METHOD

Prospective study in 192 singleton and 66 twin pregnancies with preterm labor before 34 weeks. Vaginal sonography for measurement of cervical length, and screening for fetal fibronectin in vaginal smears were performed at admission. The incidence of delivery before 34 weeks was compared with cervical length and the presence of fetal fibronectin.

RESULTS

In singleton pregnancies, delivery before 34 weeks was significantly more frequent in women with a cervical length <30 mm (26.6 vs. 2.0%; P = 0.0004), or presence of fetal fibronectin (27.5 vs. 6.0%; P = 0.001). The corresponding negative predictive values (NPV) were 98% and 94%, respectively. In twin pregnancies, receiver characteristic curve analysis showed that a cervical length of 20 mm had the highest diagnostic performance in predicting preterm delivery. The corresponding NPV was 63%. In this group, delivery before 34 weeks showed no significant difference in women with a cervical length < 30 mm (43.7 vs. 38.8%), cervical length < 20 mm (52.0 vs. 36.6%, P = 0.219), or presence of fetal fibronectin (47.6 vs. 21.7%, P = 0.0705).

DISCUSSION AND CONCLUSION

Ultrasonographic measurement of cervical length does not predict preterm delivery in twin pregnancies with preterm labor.

Evaluation of the cervix by ultrasound for the prediction of preterm birth

Across numerous investigations and study populations, the relationship between shortened cervical length and spontaneous preterm birth is consistent and compelling. However, one must recognize the imperfect test characteristics of cervical ultrasound for predicting prematurity, particularly in low-risk populations. It should be clear that this relationship supports interactions with the other anatomic components and interactive pathways that comprise the spontaneous, preterm-birth syndrome. In summary, the clinical usefulness of these observations will be realized only through further investigation into the pathophysiology of spontaneous preterm birth and through controlled, clinical-intervention trials.

Accuracy of cervical transvaginal sonography in predicting preterm birth: a systematic review

This review investigates the accuracy with which transvaginal cervical sonography predicts spontaneous preterm birth. Published studies were identified without language restrictions through nine different databases and manual searching of bibliographies of known primary and review articles. Studies were selected if they undertook antenatal transvaginal sonographic cervical assessment among a population of pregnant women with known gestational age of delivery. There were 46 primary articles, which included a total of 31,577 women, consisting of 33 studies in asymptomatic and 13 studies in symptomatic women. Data were extracted for the studies' characteristics and quality. Accuracy data were used to form 2 x 2 contingency tables for various cervical length measurements with birth before 32, 34 and 37 weeks' gestation as the reference standards. Data were stratified according to singleton or twin pregnancy, gestational age at testing, cervical length threshold, and the various reference standards, and were pooled to produce summary estimates of likelihood ratios (LRs). Our review showed that transvaginal cervical sonography identifies women who are at higher risk of spontaneous preterm birth, although there was a wide variation amongst studies with respect to gestational age at testing, definition of threshold of abnormality and definition of reference standard. The most commonly reported sub-group was testing of asymptomatic women at < 20 weeks' gestation using a threshold cervical length of 25 mm with spontaneous preterm birth before 34 weeks' gestation as the reference standard. The summary LR+ for this group was 6.29 (95% CI, 3.29-12.02), with corresponding LR- of 0.79 (95% CI, 0.65-0.95). Both cervical length measurement and funneling, whether alone or in combination, appear to be useful (depending on the threshold chosen to define the abnormality) in predicting spontaneous preterm birth in asymptomatic women. For symptomatic women there was a paucity of data, although the degree of funneling appeared to be predictive of spontaneous preterm birth.

Charts for cervical length in singleton pregnancy

OBJECTIVES

To construct charts for cervical length in a low risk population measured by transvaginal ultrasonography.

METHODS

Pregnant women of an apparently normal population were seen in the ultrasound division of the University Women's Hospital Basel between 20 and 34 weeks of gestation and underwent once (one measurement per subject) a transvaginal ultrasound measurement of the cervix under standardized conditions. In order to establish normal values of the cervical length, finally only women who delivered spontaneously at term (>37 weeks of gestation) remained in the study. Exclusion criteria were preterm labor, multiple pregnancies, cerclage or surgical intervention prior to pregnancy. For statistical evaluation, regression analysis and calculation of 5th and 95th percentiles were performed.

RESULTS

A total of 669 cervical measurements were recorded. The number of measurements differed from 22 measurements at 23 weeks of gestation to 86 at 31 weeks of gestation. Cervical length gradually and significantly decreased as the gestational age progressed (between 20 and 34 weeks of gestation). New charts with the 5th, 50th and 95th percentile are presented and compared with previously published data.

CONCLUSIONS

Our charts for cervical length in a limited risk population can be used for observing patients at high risk of preterm delivery and for clearly identifying a significant deviation or decline in the percentile for these subjects.

Cervical incompetence: a reappraisal of an obstetric controversy

Cervical incompetence is not a categoric but rather a continuous variable, meaning that there are various degrees in the competency of the cervix. Furthermore, a certain degree of competency of the cervix can be expressed differently in subsequent pregnancies. Women with risk factors for cervical incompetence in their gynecological/obstetric history should be followed by transvaginal ultrasonography. History alone is not an indication for a prophylactic cerclage. Although transvaginal ultrasonography identifies women at high risk of preterm delivery, it does not discriminate between different underlying pathologies. Short cervical length alone is not an indication for a therapeutic cerclage. Serial transvaginal ultrasonographic measurements of cervical length in women with risk factors can identify those women truly at high risk of preterm delivery. A transvaginal cervical cerclage with bed rest reduces preterm delivery and improves perinatal outcome in women with a short cervical length and risk factors for cervical incompetence.

TARGET AUDIENCE

Obstetricians & Gynecologists, Family Physicians.

LEARNING OBJECTIVES

After completion of this article, the reader will be able to define cervical incompetence, explain the role of transvaginal ultrasonography in the prediction of preterm delivery, and summarize the data on the use of transvaginal cervical cerclage.

Cervical screening for preterm delivery

The ability of sonographic cervical length screening to detect those at risk of spontaneous preterm delivery has been extensively explored over the past few years. This applies both to high-risk and low-risk groups. Cervical length measurement appears to be superior to biochemical, microbiological or hormonal methods of screening. The screening technique has been standardized, but the cervical length for intervention and the timing and nature of intervention have not been defined. Cervical cerclage appears to be of use to prevent or arrest the progress of cervical dilation in high-risk cases, but the management of the screen-positive low-risk case has yet to be determined. Future management may be stratified according to actual cervical length, and prospective randomized trials of treatment for the short cervix are needed.