Prevalence of anomalies on the routine mid-trimester ultrasound: 3172 consecutive cases by a single maternal-fetal medicine specialist

Introduction/Purpose

The routine mid-trimester fetal anatomy ultrasound (FAS) is offered to every pregnant woman and remains critical in the detection of structural fetal anomalies. Our study aimed to determine the prevalence of abnormalities on routine FAS performed by a single operator, who is an experienced sub-specialist in maternal-fetal medicine.

Methods

A retrospective analysis of all routine FAS performed a tertiary private obstetric ultrasound practice in metropolitan Sydney over a 7-year period, August 2015-July 2022. An advanced ultrasound protocol including detailed cardiac views was used in every case. Second opinion scans for suspected abnormalities were excluded. Fetal anomalies were classified into major and minor, based on the likely need for neonatal intervention.

Results

Among 14,908 obstetric ultrasound examinations, routine FAS were performed on 3172 fetuses by a single operator. More than 99% of women had screened low-risk for fetal aneuploidy. Structural anomalies were identified in 5% (157/3172) of fetuses; the prevalence of major anomalies was 1% (30/3172). Almost 60% of total anomalies were either cardiac or renal. No differences were identified in anomaly rates for singletons compared with twins (5.0% vs. 4.2%; P = 0.75). The prevalence of placenta previa and vasa previa was 10% and 0.1%, respectively.

Discussion

The prevalence of fetal anomalies on routine FAS by a single operator using a standardised protocol was higher in our practice (5%) than in previously published studies. Although most anomalies were minor, the rate of major abnormality was 1%.

Conclusion

The routine mid-trimester FAS remains an integral component of prenatal ultrasound screening.

Guideline No. 401: Sonographic Cervical Length in Singleton Pregnancies: Techniques and Clinical Applications

OBJECTIVES

• To assess the association between sonography-derived cervical length measurement and preterm birth. • To describe the various techniques to measure cervical length using sonography. • To review the natural history of the short cervix. • To review the clinical uses, predictive ability, and utility of sonography-measured short cervix.

OUTCOMES

Reduction in rates of prematurity and/or better identification of those at risk, as well as possible prevention of unnecessary interventions.

INTENDED USERS

Clinicians involved in the obstetrical management or cervical imaging of patients at increased risk of a short cervix.

TARGET POPULATION

Women at increased risk of a short cervix or at risk of preterm birth.

EVIDENCE

Literature published up to June 2019 was retrieved through searches of PubMed and the Cochrane Library using appropriate controlled vocabulary and key words (preterm labour, ultrasound, cervix, cervical insufficiency, transvaginal, transperineal, cervical length, fibronectin). Results were restricted to general and systematic reviews, randomized controlled trials, controlled clinical trials, and observational studies. There were no date or language restrictions. Grey (unpublished) literature was identified through searching the websites of health technology assessment agencies, clinical practice guideline collections, clinical trial registries, and national and international medical specialty societies.

VALUES

The evidence and this guideline were reviewed by the Diagnostic Imaging Committee of the Society of Obstetricians and Gynaecologists of Canada, and the recommendations were made and graded according to the rankings of the Canadian Task Force on Preventive Health Care (Online Appendix Table A1).

BENEFITS, HARMS, COSTS

Preterm birth is a leading cause of perinatal morbidity and mortality. Use of the sonographic technique reviewed in this guideline may help identify women at risk of preterm birth and, in some circumstances, lead to interventions that may reduce the rate of preterm birth. SUMMARY STATEMENTS (CANADIAN TASK FORCE ON PREVENTIVE HEALTH CARE GRADING IN PARENTHESES): RECOMMENDATIONS (CANADIAN TASK FORCE ON PREVENTIVE HEALTH CARE GRADING IN PARENTHESES).

Cervical length varies considering different populations and gestational outcomes: Results from a systematic review and meta-analysis

BACKGROUND

The uterine cervical length is an important risk factor for preterm birth. The aim of this study was to assess cervical length distribution in women with singleton pregnancies, measured by transvaginal ultrasound between 16 and 24 weeks, and its association with population characteristics.

MATERIALS AND METHODS

We searched electronic databases and other sources for studies published from April 1, 1990 to July 21, 2020. Of the 2019 retrieved publications, full-text versions of 137 articles were considered. We included 77 original articles that reported cervical length measurements of 363,431 women. The main aim of this study was to identify the pattern of cervical length in different populations. We collected demographic and clinical data concerning the population, in addition to information regarding the ultrasound examination and cervical length measurement. Regarding study bias, 56 were at low risk of bias and 21 were at medium risk of bias.

RESULTS

The meta-analysis included 57 articles with data from 158,346 women. The mean cervical length was 37.96. mm (95% CI [36.68, 39.24]). Cervical length was shorter in women from Africa and Asia, in those from low-income countries, with a lower body weight, and in those who delivered before 37 gestational weeks. We found that the cervical length from pooled studies is longer than that usually discussed in the literature. Regarding limitations, we had difficulty assessing our main variable because there was no consistent pattern in the way authors reported cervical length measurement. Another limitation was the great heterogeneity between studies.

CONCLUSIONS

The use of a single cutoff value to define a short cervix diagnosis, an important risk factor for preterm birth, may not be correct and cervical length must be considered according to maternal population characteristics. Future studies should identify different specific curves and cutoff values for cervical length in different populations. This meta-analysis was registered in the PROSPERO database under CRD42017070246 at https://www.crd.york.ac.uk/prospero/display_record.php?RecordID=70246.

Comparison of transabdominal and transvaginal ultrasonography for the assessment of cervical length in the third trimester of pregnancy

OBJECTIVE

This study aimed to compare TA and transvaginal (TV) ultrasound assessment of cervical length (CL), as well as to assess the feasibility of the TA approach in the third trimester of pregnancy.

MATERIALS AND METHODS

This was prospective study of low-risk women at 31-34 gestational weeks who underwent TA and TV CL measurements during a routine 3rd trimester scan. All examinations were performed by one operator who was blind to the measurements. Differences between the two methods were evaluated.

RESULTS

240 women were initially enrolled in the study. Paired TA and TV measurements were obtained in 123 (51.3%) women. The mean TV CL was 35.2 ± 6.8 mm and the mean TA CL was 34.7 ± 6.5 mm. There was a significant correlation between the CL measured by the two different methods (r = 0.816). No significant differences were identified between the mean CL measurements of the two techniques (t = -1.360; p = 0.176). Moreover, regarding the feasibility of TA technique, it was less likely to obtain TA CL images in cases with a cephalic fetal presentation (p = 0.028).

CONCLUSION

At 31-34 gestational weeks, with an empty bladder, the cervix can be visualized by the TA approach in only about half of the cases (51.3%). The TA CL measurements show a significant correlation with the TV ones. More research is needed to determine the potential predictive value of the TA ultrasound for preterm labor.

Correlation of transabdominal and transvaginal sonography for the assessment of uterocervical angle at 16-24 weeks' gestation

The objective of this study was to determine the correlation between transabdominal (TAS) and transvaginal sonography (TVS) uterocervical angle (UCA) measurement in pregnant women with no history of previous preterm birth. A cross-sectional study involving singleton pregnancies between 16 and 24 weeks of gestation who underwent routine foetal anatomical scan was conducted. The TAS-UCA measurement was performed before voiding and with an empty bladder. A total of 256 women completed the sonography. The mean maternal age was 32 ± 6.68 years. The mean gestation age at the time of ultrasound assessment was 19 ± 1.71 weeks. The mean prevoid TAS-UCA was 119.74 ± 33.12° and the mean postvoid TAS-UCA was 110.73 ± 25.30°. There was a significant difference between prevoid and postvoid TAS-UCA measurement (p < .05). The mean TVS-UCA was 103.91 ± 26.42°. The Pearson correlation coefficients of prevoid and postvoid TAS-UCA with TVS-UCA were 0.438 and 0.601, respectively. In conclusion, the postvoid TAS-UCA has moderate correlation with TVS-UCA measurement and is better than the prevoid TAS-UCA in women with low risk for preterm birth.IMPACT STATEMENTWhat is already known on this subject? TVS is the gold standard for cervical length (CL) assessment for prediction preterm birth. However, TVS requires an experienced or trained sonographer and some women decline TVS because of the embarrassment and discomfort during examination. Several studies have demonstrated the correlation between TAS and TVS and suggested that TAS could be an alternative for CL screening. UCA has been reported as a new predictor of spontaneous preterm birth and is usually performed by TVS. Thus, it is interesting to evaluate whether TAS can be a substitute procedure for TVS in UCA measurement.What the results of this study add? TAS may be used as a substitute procedure for TVS and the postvoid TAS is more appropriate than prevoid TAS for UCA measurement.What the implications are of these findings for clinical practice and/or further research? TAS may be an alternative method for UCA measurement when TVS is unavailable or in pregnant women who decline TVS-UCA measurement. However, further study should be conducted to confirm the association between TVS-UCA and postvoid TAS-UCA before deciding to use postvoid TAS-UCA as a screening tool for preterm prediction.

Can Transabdominal Scan Predict a Short Cervix by Transvaginal Scan?

Background. To determine whether transabdominal screening can be used to screen women with short cervix on transvaginal scan. Methods. The study was done between 18 and 20 weeks of gestation. Transabdominal scan was done and cervical length was measured. Transvaginal scan was also done and cervical length was measured. An attempt was made to find out whether transabdominal scan be used to predict a cervical length of 25 mm by transvaginal scan. Results. In our study the cut-off for transabdominal scan for detecting a short cervix of 25 mm by transvaginal scan was 29 mm. A transabdominal cervical length of 29 mm could predict a short cervix of 25 mm by transvaginal scan by 100% sensitivity and 92.4% sensitivity. Conclusion. A cut-off of 29 mm by transabdominal scan is very accurate in predicting a short cervix of 25 mm by transvaginal scan.

Transabdominal ultrasound is appropriate

Preterm birth remains a major cause of perinatal morbidity and mortality. A short cervix is strongly associated with spontaneous preterm birth. Professional organizations support cervical length screening for singleton gestations with a prior spontaneous preterm birth and second-trimester cervical length measurements between 16-24 weeks. All interventions used to decrease the risk of preterm birth in women with a short cervix are based on clinical trials that used transvaginal cervical length measurement, but transabdominal ultrasound has been shown to correlate well with transvaginal measurement in some observational studies. Transvaginal cervical length measurement is more accurate and more reliably obtained than the transabdominal approach. Conversely, transabdominal ultrasound could have the advantage of ease of implementation and, in general, is perceived by patients to be associated with less discomfort. Currently, there is no randomized clinical study that compares head-to-head the effectiveness of transvaginal vs transabdominal ultrasound for preterm birth risk screening. This point/counterpoint article summarizes the pros and cons of the 2 ultrasound approaches and debates whether transvaginal ultrasound should be used exclusively or if transabdominal ultrasound can be incorporated in cervical length screening for prevention of preterm birth.

Not transabdominal!

Preterm birth remains a major cause of perinatal morbidity and mortality. A short cervix is strongly associated with spontaneous preterm birth. Professional organizations support cervical length screening for singleton gestations with a prior spontaneous preterm birth and second-trimester cervical length measurements between 16-24 weeks. All interventions used to decrease the risk of preterm birth in women with a short cervix are based on clinical trials that used transvaginal cervical length measurement, but transabdominal ultrasound has been shown to correlate well with transvaginal measurement in some observational studies. Transvaginal cervical length measurement is more accurate and more reliably obtained than the transabdominal approach. Conversely, transabdominal ultrasound could have the advantage of ease of implementation and, in general, is perceived by patients to be associated with less discomfort. Currently, there is no randomized clinical study that compares head-to-head the effectiveness of transvaginal vs transabdominal ultrasound for preterm birth risk screening. This point/counterpoint article summarizes the pros and cons of the 2 ultrasound approaches and debates whether transvaginal ultrasound should be used exclusively or if transabdominal ultrasound can be incorporated in cervical length screening for prevention of preterm birth.

Comparison of transabdominal and transvaginal ultrasonography for the assessment of cervical length at 16-23 weeks of gestation

The aim of this study was to assess the relationship between transabdominal and transvaginal ultrasonography for the cervical length assessment and to evaluate the predictive value of the transabdominal ultrasonography cervical length assessment for predicting preterm birth. A prospective cohort study was conducted. Transabdominal and transvaginal ultrasonography cervical length assessments were performed in 160 pregnant women between 16 and 23 ^+ 6 weeks of gestation. Transabdominal ultrasonography cervical length assessment was positively correlated with the transvaginal ultrasonography cervical length assessment. Mean ± standard deviation of the cervical length was significantly different between transabdominal and transvaginal ultrasonography (36.4 ± 5.4 vs. 41.2 ± 5.4 mm, p < .001). Transabdominal cervical length was shorter than the transvaginal cervical length with a mean difference of 4.8 mm. The sensitivity, specificity, positive predictive value and negative predictive value for predicting preterm birth when the transabdominal cervical length was ≤35 mm, were 50%, 52.1%, 9.1%, and 91.6%, respectively. In conclusion, transabdominal ultrasonography cervical length assessment is positively correlated with the transvaginal ultrasonography cervical length assessment. Transabdominal cervical length assessment was not a good predictor of preterm birth.

Universal cervical length screening in singleton gestations without a previous preterm birth: ten reasons why it should be implemented

A short cervix is associated strongly with preterm birth. Pharmacologic intervention with vaginal progesterone in women with a singleton pregnancy and a short cervix in the second trimester decreases the incidence of preterm birth. We explore the evidence that universal cervical length screening in women with a singleton pregnancy meets the criteria for an effective screening test for preterm birth prevention, driving it towards becoming routinely offered in prenatal care.

Cervical length measurement: Comparison of transabdominal and transvaginal approach

Objective: To compare transabdominal (TA) and transvaginal (TV) ultrasound assessment of cervical length at 16–41 weeks gestation.

Methods: TA and TV ultrasound measurements of cervical length were made on 491 pregnancies of 16–41 weeks gestation. Cervical length was measured from internal to external cervical os. Bland‐Altman plots and Wilcoxon signed rank test were used to evaluate differences between TA and TV measurements.

Results: The validity of the TA method depended on cervical length. Although the TA method underestimated cervical length by 2.0 mm on average (P < 0.001), Bland Altman plots showed an inverse trend with shorter cervixes. In women with a cervix < 25 mm (n = 30) based on TV scan measurement, TA overestimated cervical length by 12 mm (P < 0.001). The sensitivity and specificity of TA as a test to detect cervical length < 25 mm were 10% (95% CI: 2.1–26%) and 94% (95% CI: 92–96%) respectively; the negative LR was 0.96 (95% CI: 0.84–1.08). The maximum area under the ROC curve would be obtained at a TA cut‐off = 32 mm (to detect a cervix < 25 mm), corresponding to a sensitivity of 77% and a specificity of 58%.

Conclusion: TA measurements do not reflect TV assessment accurately, particularly if the cervix is short. At 24–34 weeks, a policy of proceeding to TV scan if TA measurement is < 25 mm will only detect 10% of affected pregnancies and has a poor positive predictive value so is of limited value as a predictive tool for women attending with symptoms and signs of preterm labour > 24 weeks gestation. There is no value in TA assessment of the cervix > 36 weeks.

The capacity of mid-pregnancy cervical length to predict preterm birth in low-risk women: a national cohort study

INTRODUCTION

We investigated the predictive capacity of mid-trimester cervical length (CL) measurement for spontaneous and iatrogenic preterm birth.

MATERIAL AND METHODS

We performed a prospective observational cohort study in nulliparous women and low-risk multiparous women with a singleton pregnancy between 16(+0) and 21(+6) weeks of gestation. We assessed the prognostic capacity of transvaginally measured mid-trimester CL for spontaneous and iatrogenic preterm birth (<37 weeks) using likelihood ratios (LR) and receiver-operating-characteristic analysis. We calculated numbers needed to screen to prevent one preterm birth assuming different treatment effects. Main outcome measures were preterm birth <32, <34 and <37 weeks.

RESULTS

We studied 11,943 women, of whom 666 (5.6%) delivered preterm: 464 (3.9%) spontaneous and 202 (1.7%) iatrogenic. Mean CL was 44.1 mm (SD 7.8 mm). In nulliparous women, the LRs for spontaneous preterm birth varied between 27 (95% CI 7.7-95) for a CL ≤ 20 mm, and 2.0 (95% CI 1.6-2.5) for a CL between 30 and 35 mm. For low-risk multiparous women, these LRs were 37 (95% CI 7.5-182) and 1.5 (95% CI 0.97-2.2), respectively. Using a cut-off for CL ≤ 30 mm, 28 (6.0%) of 464 women with spontaneous preterm birth were identified. The number needed to screen to prevent one case of preterm birth was 618 in nulliparous women and 1417 for low-risk multiparous women (40% treatment effect, cut-off 30 mm).

CONCLUSION

In women at low risk of preterm birth, CL predicts spontaneous preterm birth. However, its isolated use as a screening tool has limited value due to low sensitivity.

Prospective evaluation of a protocol for using transabdominal ultrasound to screen for short cervix

OBJECTIVE

We sought to evaluate a recently proposed protocol whereby transabdominal ultrasound of the cervix might be used as a prescreen to select women to undergo or to forgo measurement of cervical length via transvaginal ultrasound (CLvag).

STUDY DESIGN

This was a prospective cohort study. Measurements of cervical length via transabdominal ultrasound (CLabd) and CLvag were made in women with singleton pregnancy during routine obstetrical ultrasound examination at 18(0/7) to 23(6/7) weeks of gestation. The transabdominal screen was considered positive if CLabd was ≤36 mm with the maternal bladder full or ≤35 mm with the bladder empty, or adequate imaging of the cervix could not be obtained. Sensitivity, specificity, predictive values, and likelihood ratios of a positive screen to detect a short cervix (CLvag ≤25 mm) were calculated.

RESULTS

An interim analysis identified several technical problems with CLabd measurements, so the protocol was extensively revised. Under the revised protocol, 1580 women were included. Adequate views of the cervix were obtained via transabdominal imaging in 46% of subjects with the bladder empty and 56% with the bladder full. The correlation between CLabd and CLvag was poor (r = 0.38). Of the 17 patients with a short cervix, 15 had suboptimal transabdominal exams (screen positive) and 2 had CLabd ≤35 mm with bladder empty (screen positive). Sensitivity of the screen was 100% (95% confidence interval, 80.5-100%) but specificity was only 32.2% (95% confidence interval, 29.9-34.6%) and screen positive rate was 66.3%. Several technical problems and limitations of transabdominal imaging of the cervix are shown.

CONCLUSION

Using modern, high-resolution ultrasound equipment, we were unable to adequately image the cervix via transabdominal ultrasound in half the cases. Although we confirmed that a CLabd cutoff value of 35-36 mm is appropriate for detection of short cervix, the technique for measuring CLabd is fraught with technical problems. Practitioners must validate the technique in their own practice before adopting this or similar prescreening protocols. We decided not to adopt this protocol.

Cervical length screening: a randomized trial assessing the impact on visit length and patient attitudes

OBJECTIVES

The purpose of this study was to quantify the time required for transvaginal cervical length measurements during a second-trimester anatomy scan and to evaluate patient attitudes regarding cervical length assessment.

METHODS

Consenting women were randomly assigned to one of the following: (1) standard arm-cervix visualized, no prespecified cervical length measurement; (2) sequential arm-3 transabdominal cervical length measurements obtained, transvaginal sonography performed if images were inadequate or if any measurement was 3 cm or less; and (3) screening transvaginal sonography arm-3 transvaginal cervical length measurements obtained. Times were recorded for the entire examination and cervical length evaluation. Participants completed a questionnaire at the end of their visits.

RESULTS

Sixty of 230 eligible women enrolled. Demographic characteristics were similar across groups except for body mass index, which was greater in the sequential arm than the screening arm (mean ± SD, 28.5 ± 7.75 versus 24.7 ± 3.89 kg/m(2); P = .03). There were no differences in total examination times between the 3 arms (24.8 ± 8.59 versus 27.8 ± 8.75 versus 28.5 ± 7.78 minutes; P= .39). There were no differences across groups in participant attitudes regarding examination discomfort or embarrassment.

CONCLUSIONS

Performing screening transvaginal sonography to measure cervical length did not have a statistically significant impact on the amount of time for completion of the entire examination. Participants had positive responses regarding cervical length assessment by transabdominal and transvaginal sonography.

Association between shortened cervical length at 34-36 weeks' gestation and term labour in Asian women

Cervical length was measured at 34-36 weeks' gestation by transvaginal ultrasound. The purpose of measurement of cervical length before term was to reveal the association with the onset of term labour. This was a retrospective study of 362 women who were delivered at term at Mizmedi hospital, between August 2006 and November 2011. There was significant linear correlation between cervical length and the scan-to-labour interval in women with labour before 41 weeks. The measurement of cervical length at 34-36 weeks' gestation might be helpful in predicting the onset of term labour before 41 weeks.

Is transabdominal ultrasound scanning of cervical measurement in mid-trimester pregnancy a useful alternative to transvaginal ultrasound scan?

OBJECTIVE

The aim of this study is to assess the correlation between transabdominal and transvaginal ultrasound measurements of the cervix in pregnancy. If transabdominal ultrasound measurement of cervical length is found to provide effective information, it could be used in patient counselling and when making clinical decisions.

MATERIAL AND METHODS

One hundred and twenty seven pregnant patients between 18-26 weeks of pregnancy were enrolled in this prospective study for measuring cervical length, both by transabdominal and transvaginal ultrasound scan after bladder emptying. Transabdominal and transvaginal measurements were compared and correlated.

RESULTS

In patients with transvaginal ultrasound scan (TVS) cervical length ≤32 mm, TVS cervical length was found to be shorter than by transabdominal ultrasound scan (TAS). Most of these patients needed >3 cm of vertical pocket of urine in the bladder for adequate visualisation of the cervix. In patients with TVS cervical length >32 mm, the TVS measurement of the cervix was longer than the TAS measurement of the cervix. In these patients, the cervix could be seen by TAS when there was either ≤3 cm vertical pocket of urine in the bladder or an empty bladder. Statistical tests showed that there is a significant difference between TAS and TVS cervical measurements and that there is a significant association between these two measurements.

CONCLUSION

Most of the patients needed variable degrees of bladder filling for adequate visualisation of the cervix. Although minimal bladder filling does not influence TAS measurements of cervical length, moderate fullness of the bladder does cause an apparent increase in TAS measurements of cervical length. If the cervical length is ≥30 mm by TAS, regardless of urine content in the bladder, the patient can be assured vis a vis their risk of preterm labour as far as cervical length is concerned. However, in patients with TAS cervical measurement <30 mm and where the bladder needed a moderate amount of urine for adequate visualisation of the cervix, TVS cervical measurement may be close to the critical value of 25 mm. These patients need to be counselled and offered TVS for better assessment of cervical length.

Cost-effectiveness of transabdominal ultrasound for cervical length screening for preterm birth prevention

OBJECTIVE

Transabdominal ultrasound (TAUS) cervical length (CL) screening has been proposed as an alternative to universal transvaginal screening to identify women at an increased risk of preterm birth. We sought to identify whether and under what circumstances TAUS would be cost-effective.

STUDY DESIGN

This is a decision analytic model designed to compare an initial TAUS CL screening approach with universal transvaginal screening in a hypothetical cohort of women with a singleton pregnancy. Cost, probability, and utility estimates were derived from the existing literature.

RESULTS

Under baseline assumptions, universal transvaginal was the dominant strategy. In comparison to TAUS, universal transvaginal CL screening reduced preterm birth by 0.03%, reduced costs by $1.2 million and increased quality-adjusted life years by 70 per 100,000 women. Although robust to many changes in many estimates, the model was sensitive to the cost of a transvaginal ultrasound, the prevalence of a short cervix and the test characteristics (ie, sensitivity and specificity) of a TAUS screening examination for short CL.

CONCLUSION

Compared with an initial TAUS screen, universal transvaginal ultrasound was a more cost-effective strategy under most assumptions. Optimizing TAUS testing characteristics or applying a transabdominal screening strategy in lower risk populations may yield an initial TAUS to be cost-effective.

Comparison of cervical lengths using transabdominal and transvaginal sonography in midpregnancy

OBJECTIVES

Cervical length assessment is helpful to predict and prevent preterm birth. However, transvaginal sonography is not easy to perform. The aim of this study was to investigate the relationship and discrepancies between cervical lengths measured by transabdominal and transvaginal sonography in midpregnancy.

METHODS

Transabdominal and transvaginal cervical lengths were measured in 255 pregnant women between 20 and 29 gestational weeks. The discrepancies in cervical lengths between the two methods were analyzed for the following maternal and fetal conditions: (1) vertex versus breech fetal presentation, (2) whether the fetal presenting part overlay the cervical internal os, (3) whether both the internal os and external os were visible or only the internal os was clearly visible, (4) maternal bladder filling status, (5) maternal age, (6) parity, and (7) gestational age.

RESULTS

The mean cervical lengths were not significantly different (mean ± SD, 3.88 ± 0.73 cm on transabdominal sonography and 3.93 ± 0.72 cm on transvaginal sonography; P = .129; Pearson r = 0.75). The 5th-percentile transabdominal cervical length was 26.0 mm, and the transvaginal length was 27.8 mm. There were significant discrepancies between the two methods in the cases in which a fetal presenting part overlay the internal os, in the cases in which the external os was not clearly visible, and in primiparous women. Transabdominal cervical measurements were consistently shorter than transvaginal measurements in the cases with discrepancies.

CONCLUSIONS

Transabdominal cervical length measurements are correlated with transvaginal measurements overall, and the transabdominal length is consistently shorter than the transvaginal length in cases with discrepancies. Transabdominal sonography could be used as a cervical length screening tool.

Cervical length for predicting preterm birth and a comparison of ultrasonic measurement techniques

Introduction: Preterm birth is the leading cause of neonatal morbidity and mortality not attributable to congenital anomalies or aneuploidy. It has been shown that a shortened cervix is a powerful indicator of preterm births in women with singleton and twin gestations - the shorter the cervical length, the higher the risk of spontaneous preterm birth. Ultrasound measurements of the cervix are a more accurate way of determining cervical length (CL) than using a digital method. Background: There are three approaches that may be used to perform ultrasound measurements of the cervix; these are the transabdominal (TA), transperineal (TP) and the transvaginal (TV) approach. The TV approach is considered to be the gold standard. In women who are considered to be at a high risk of preterm birth it is now recommended that the cervix is measured at the mid-trimester ultrasound using the TV ultrasound approach. For women considered to be at a historical low risk the TV scan is not recommended, however it has been found that many women who deliver a preterm baby have no known risk factors. Conclusion: There is contradictory evidence in the literature with regard to the correlation between TA, TP and TV measurements. This article provides an overview of these three approaches with a focus on the clinical value for the assessment of the maternal cervix.

Can transabdominal ultrasound identify women at high risk for short cervical length?

OBJECTIVE

To determine whether transabdominal cervical length screening could identify women at high risk for having a short cervix on transvaginal ultrasound.

DESIGN

Retrospective cohort study.

SETTING

Tertiary referral center.

POPULATION

A total of 703 patients with a singleton pregnancy at 18 to 23(+6) weeks of gestation who underwent transabdominal and transvaginal cervical length assessment during anatomy ultrasound at a single institution between January 2007 and October 2011.

METHODS

Electronic medical records were reviewed to identify women who met the study criteria.

MAIN OUTCOME MEASURES

The primary outcome was the number of women with a short transabdominal cervical length (defined as ≤ 30 mm) who needed to undergo transvaginal ultrasound to detect one woman with a short transvaginal cervical length of ≤ 20 mm.

RESULTS

In all, 703 patients were included in the primary analysis; 3.42 women with transabdominal cervical length ≤ 30 mm needed to undergo transvaginal ultrasound to detect one woman with transvaginal ultrasound cervical length ≤ 20 mm. Of women with short transvaginal cervical length ≤ 20 mm, 89.8% had a transabdominal measurement ≤ 30 mm and 96.7% had a transabdominal measurement ≤ 33 mm.

CONCLUSIONS

Screening of transabdominal cervical length may represent a useful strategy for detecting women with short cervix on transvaginal ultrasound.

Can transabdominal ultrasound be used as a screening test for short cervical length?

OBJECTIVE

Universal transvaginal cervical length screening can be associated with a significant logistical burden. We hypothesized that there is a threshold cervical length measured by transabdominal ultrasound above which risk for short transvaginal cervical length is extremely low.

STUDY DESIGN

This prospective cohort study evaluated a consecutive series of women offered universal transvaginal cervical length screening during anatomy ultrasound. Transabdominal measurement of the cervix-obtained before and after voiding for each patient-was performed before transvaginal ultrasound. The study was powered to detect a transabdominal cervical length cutoff with 95% sensitivity (95% confidence interval, 90-99%) for transvaginal cervical length of ≤25 mm.

RESULTS

One thousand two hundred seventeen women were included in the analysis. Prevoid transabdominal cervical length ≤36 mm detects 96% of transvaginal cervical lengths ≤25 mm with 39% specificity. A prevoid transabdominal cervical length ≤35 mm detects 100% of transvaginal cervical lengths ≤20 mm with 41% specificity. Transabdominal images of the cervix could not be obtained in 6.2% of women prevoid and 17.9% of women postvoid.

CONCLUSION

Transabdominal cervical length screening successfully identifies women at very low risk for short transvaginal cervical length. Transabdominal screening may significantly reduce the burden of universal cervical length screening by allowing approximately 40% of women to avoid transvaginal ultrasound. To ensure high sensitivity of transabdominal screening, approximately 60% of patients will still require a transvaginal study.

Transabdominal evaluation of uterine cervical length during pregnancy fails to identify a substantial number of women with a short cervix

OBJECTIVE

To assess the diagnostic performance of transabdominal sonographic measurement of cervical length in identifying patients with a short cervix.

METHODS

Cervical length was measured in 220 pregnant women using transabdominal and transvaginal ultrasound (US). Reproducibility and agreement between and within both methods were assessed. The diagnostic accuracy of transabdominal US for identifying cases with a cervical length <25 mm was evaluated.

RESULTS

Twenty-one out of 220 cases (9.5%) had a cervical length <25 mm by transvaginal US. Only 43% (n = 9) of patients with a short cervix were correctly identified by transabdominal US. In patients with a cervical length of <25 mm by transvaginal US, transabdominal measurement of the cervix overestimated this parameter by an average of 8 mm (95% LOAs, -26.4 to 10.5 mm). Among women without a short cervix, transabdominal US underestimated cervical length on average (LOA) by 1.1 mm (95% LOAs, -11.0 to 13.2 mm). Transvaginal US was also more reproducible (intraclass correlation coefficient: (ICC) (0.96; 95% CI, 0.94 to 0.97) based on comparisons between 2D images and immediately acquired 3D volume datasets relative to transabdominal US (ICC: 0.71; 95% CI, 0.57 to 0.84). Transvaginal US detected 13 cases with funneling and six cases with sludge whereas only three cases of funneling and one of sludge were detected by transabdominal US.

CONCLUSION

Transabdominal measurement overestimated cervical LOA by 8 mm among women with a short cervix and resulted in the underdiagnosis of 57% of cases.