Transvaginal ultrasonography examination of the uterine cervix in hospitalised women undergoing preterm labour

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 Grey (unpublished) literature was identified through searching the websites of health technology assessment agencies, clinical practice guideline collections, clinical trial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).

Predictive value of cervical length in women with twin pregnancy presenting with threatened preterm labor

OBJECTIVE

To assess the accuracy and determine the optimal threshold of sonographic cervical length (CL) for the prediction of preterm delivery (PTD) in women with twin pregnancies presenting with threatened preterm labor (PTL).

METHODS

This was a retrospective study of women with twin pregnancies who presented with threatened PTL and underwent sonographic measurement of CL in a tertiary center. The accuracy of CL in predicting PTD in women with twin pregnancies was compared with that in a control group of women with singleton pregnancies.

RESULTS

Overall, 218 women with a twin pregnancy and 1077 women with a singleton pregnancy, who presented with PTL, were included in the study. The performance of CL as a predictive test for PTD was similar in twins and singletons, as reflected by the similar correlation between CL and the examination-to-delivery interval (r, 0.30 vs 0.29; P = 0.9), the similar association of CL with risk of PTD, and the similar areas under the receiver-operating characteristics curves for differing delivery outcomes (range, 0.653-0.724 vs 0.620-0.682, respectively; P = 0.3). The optimal threshold of CL for any given target sensitivity or specificity was lower in twin than in singleton pregnancies. However, in order to achieve a negative predictive value of 95%, a higher threshold (28-30 mm) should be used in twin pregnancies. Using this twin-specific CL threshold, women with twins who present with PTL are more likely to have a positive CL test, and therefore to require subsequent interventions, than are women with singleton pregnancies with PTL (55% vs 4.2%, respectively).

CONCLUSION

In women with PTL, the performance of CL as a test for the prediction of PTD is similar in twin and singleton pregnancies. However, the optimal threshold of CL for the prediction of PTD appears to be higher in twin pregnancies, mainly owing to the higher baseline risk for PTD in these pregnancies.

Cervical length measurement for the prediction of preterm birth in symptomatic women with a twin pregnancy: a systematic review and meta-analysis

Objective. The aim of this study was to assess whether cervical length measurement (CL) could predict preterm birth (PTB) in symptomatic women with a twin pregnancy. Methods. We searched MEDLINE and EMBASE to identify studies investigating the accuracy of CL measurement in predicting PTB in symptomatic women with a twin pregnancy. We extracted data to construct two-by-two tables and used bivariate meta-analysis to generate point estimates of sensitivity and specificity. Results. Five studies (N = 226) were included. Variation in definition of PTB and cut-off points for CL was strong. One study investigated delivery within seven days, demonstrating a sensitivity of 1.0 (95% CI: 0.83–1.0) and a specificity of 0.31 (95% CI 0.2–0.43) for a CL cutoff at 25 mm. Three studies reported on predicting PTB < 37 weeks at a CL cutoff of 30 mm, with sROC point estimates of 0.76 (95% CI: 0.66 to 0.84) and 0.37 (95% CI: 0.21 to 0.56) for sensitivity and specificity, respectively. For preterm birth <34 weeks, no pooled estimates could be estimated since only 2 studies with large heterogeneity were identified. Conclusions. There is limited evidence on the accuracy of cervical length measurement testing the prediction of preterm birth in symptomatic women with a twin pregnancy, especially on the most important outcome, that is, delivery within 7 days.

[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.

SOGC Clinical Practice Guideline. Ultrasonographic cervical length assessment in predicting preterm birth in singleton pregnancies

OBJECTIVES

To review (1) the use of ultrasonographic-derived cervical length measurement in predicting preterm birth and (2) interventions associated with a short cervical length.

OUTCOMES

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

EVIDENCE

Published literature was retrieved through searches of PubMed and The Cochrane Library up to December 2009, using appropriate controlled vocabulary and key words (preterm labour, ultrasound, cervix, incompetent cervix, 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 and health technology assessment-related 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 and the Maternal Fetal Medicine Committee of the Society of Obstetricians and Gynaecologists of Canada, and the recommendations were made according to the guidelines developed by The Canadian Task Force on Preventive Health Care (Table 1).

BENEFITS, HARMS, AND COSTS

Preterm birth is a leading cause of perinatal morbidity and mortality. Use of the ultrasonographic 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.

SPONSORS

The Society of Obstetricians and Gynaecologists of Canada.

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 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.

Use of transvaginal ultrasonography to predict preterm birth in women with a history of preterm birth

OBJECTIVE

To investigate whether cervical length measured by transvaginal ultrasonography predicts spontaneous preterm birth at < 35 weeks' gestation in women with a history of spontaneous preterm birth, stratified by spontaneous preterm birth history subtype (preterm premature rupture of membranes (PPROM) or preterm labor with intact membranes at onset of labor).

METHODS

This retrospective cohort study included women with a history of spontaneous preterm birth that were subsequently pregnant with singleton gestations, compared with a low-risk control group. Transvaginal ultrasonographic cervical lengths were measured at 24 to 30 weeks of gestation. The primary outcome was spontaneous preterm birth at < 35 weeks. Secondary outcomes included spontaneous preterm birth at < 37 weeks and < 34 weeks, low birth weight, Cesarean delivery and perinatal morbidity and mortality. Multiple logistic regression analysis was used to control for potential confounders and calculate odds ratios and 95% confidence intervals. Receiver-operating characteristics (ROC) curves were used to determine the best cut-off for transvaginal ultrasound cervical length in predicting spontaneous preterm birth at < 35 weeks.

RESULTS

Women with a history of spontaneous preterm birth with intact membranes at onset of labor (n = 42) had a shorter cervical length (3.28 cm) than women with a history of spontaneous preterm birth with PPROM at onset of labor (n = 48, cervical length 3.77 cm; P = 0.019), and both subgroups had shorter cervical lengths than the low-risk control group (n = 103, cervical length 4.30 cm; P < 0.0001). Both subgroups were associated with spontaneous preterm birth at < 35 weeks, < 37 weeks, < 34 weeks and birth weight < 2500 g. ROC curves determined that the best cut-off for cervical length to predict spontaneous preterm birth at < 35 weeks was 3.0 cm. By multiple logistic regression analysis, the only independent predictors of spontaneous preterm birth at < 35 weeks were cervical length < 3.0 cm, a history of spontaneous preterm birth and antepartum bleeding in the current pregnancy. In women with a history of spontaneous preterm birth, a cervical length as measured by transvaginal ultrasonography of < 3.0 cm had a sensitivity of 63.6%, specificity of 77.2%, positive predictive value of 28.0% and negative predictive value of 93.8%, for preterm birth at < 35 weeks.

CONCLUSION

Women with a history of spontaneous preterm birth with preterm labor and intact membranes at the onset of labor have shorter cervices than women with a history of spontaneous preterm birth and PPROM at the onset of labor, and both groups have shorter cervices than a low-risk control group. Both groups of women with a history of spontaneous preterm birth have an increased risk of recurrent spontaneous preterm birth at < 35 weeks, and this is predicted by a transvaginal ultrasound cervical length of < 3.0 cm.

Transvaginal sonographic measurement of cervical length to predict preterm birth in asymptomatic women at increased risk: a systematic review

OBJECTIVES

To estimate the ability of cervical length measured by transvaginal ultrasonography in asymptomatic high-risk women to predict spontaneous preterm birth.

METHODS

MEDLINE, PubMed, EMBASE and the Cochrane Library were searched for articles published in any language between January 1980 and July 2006, using the keywords 'transvaginal ultrasonography' or ('cervix' and ('ultrasound' or 'ultrasonography' or 'sonography')); and ('preterm' or 'premature') and ('delivery' or 'labour/labor' or 'birth'), identifying cohort studies evaluating transvaginal ultrasonographic cervical length measurement in predicting preterm birth in asymptomatic women who were considered at increased risk (because of a history of spontaneous preterm birth, uterine anomalies or excisional cervical procedures), with intact membranes and singleton gestations. The primary analysis included all studies meeting the inclusion criteria. Secondary analyses were also performed specifically for (1) women with a history of spontaneous preterm birth; (2) those who had undergone an excisional cervical procedure; and (3) those with uterine anomalies.

RESULTS

Fourteen of 322 articles identified (involving 2258 women) met the criteria for systematic review. Cervical length measured by transvaginal ultrasonography predicted spontaneous preterm birth. The shorter the cervical length cut-off the higher the positive likelihood ratio (LR). The most common cervical length cut-off was < 25 mm. Using this cut-off to predict spontaneous preterm birth at < 35 weeks, transvaginal ultrasonography at < 20 weeks' gestation revealed LR+ = 4.31 (95% CI, 3.08-6.01); at 20-24 weeks, LR+ = 2.78 (95% CI, 2.22-3.49); and at > 24 weeks, LR+ = 4.01 (95% CI, 2.53-6.34). In women with a history of spontaneous preterm birth (six studies involving 663 women) cervical length at < 20 weeks revealed LR+ = 11.30 (95% CI, 3.59-35.57) and at 20-24 weeks LR+ = 2.86 (95% CI, 2.12-3.87), but there were limited data on the use of cervical length of more than 24 weeks in this group (one study involving 42 women). In women who had had excisional cervical procedures, two studies presented data on cervical length (one at < 24 weeks and one at > 24 weeks), finding cervical length at < 24 weeks to be predictive of spontaneous preterm birth at < 35 weeks (LR+ = 2.91, 95% CI, 1.69-5.01). One study (of 64 women) evaluated cervical length in women with uterine anomalies, finding it predictive of spontaneous preterm birth at < 35 weeks (LR+ = 8.14, 95% CI, 3.12-21.25).

CONCLUSION

Cervical length measured by transvaginal ultrasonography in asymptomatic high-risk women predicts spontaneous preterm birth at < 35 weeks. Further research may be warranted to evaluate the use of transvaginal ultrasonography after 24 weeks' gestation in women with a history of spontaneous preterm birth, and in women with uterine anomalies.

A systematic review and quality assessment of systematic reviews of fetal fibronectin and transvaginal length for predicting preterm birth

This systematic review aims to identify reviews of fetal fibronectin and transvaginal cervical length for predicting preterm birth, so that these could be appraised and the findings from good quality reviews highlighted. Reviews, rather than individual studies, are the basis for this systematic review because of the proliferation of reviews and the benefits of a single, consistent appraisal and assessment of evidence from these reviews, rather than further attempts to find and appraise the many individual studies in the literature. Potentially eligible reviews were sought primarily through searches of the electronic databases MEDLINE (1966-2005), EMBASE (1980-2005), CINHAL (1982-2005), Science Citation Index (1970-2005) and The Cochrane Library (Issue 3, 2005). Our systematic review consists of a description of the two factors that might be predictive of preterm birth and for which at least one relevant review was found. The scope and quality of the identified review(s) are described, and their conclusions and the strength of these conclusions discussed. Ten reviews were identified, of which seven were included in this systematic review of reviews. The quality of each review is assessed within the following domains; the extent of searching undertaken, description of study selection and inclusion criteria, comparability of included studies, assessment of publication bias, assessment of heterogeneity and conduct of sensitivity analyses. The reviews we identified show that cervicovaginal fetal fibronectin and transvaginal sonographic cervical length measurements are clinically useful factors in predicting preterm birth. Consideration might be given to the use of both the measurement of cervicovaginal fetal fibronectin and transvaginal sonographic assessment of cervical length to identify women at increased risk of preterm birth and, potentially, to improve the outcome for these women and their babies.

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.

Predictors of preterm birth

OBJECTIVE

This is a systematic review to assess published scientific evidence on preterm birth predictors.

METHODS

An Internet search for predictors of preterm birth was performed and the evidence level of each method was evaluated.

RESULTS

There is strong evidence that preterm birth can be predicted using vaginal sonography to evaluate cervical characteristics, fetal fibronectin in cervicovaginal secretions and interleukin-6 in amniotic fluid. There is consistent evidence that digital cervical examination is a weak predictor, and controversy regarding home uterine activity monitoring. There is scanty evidence about the predictive ability of maternal history and perceptions of symptoms since the study design fails to provide high evidence level.

CONCLUSION

Cervical evaluation by vaginal sonography, fetal fibronectin and interleukin-6 are the best methods for predicting preterm birth.

Impact of ultrasound cervical length assessment on duration of hospital stay in the clinical management of threatened preterm labor

OBJECTIVE

To evaluate the impact of ultrasound cervical length measurement on duration of hospital stay in patients admitted for threatened preterm labor.

STUDY DESIGN

This was a prospective, comparative study in 294 patients with threatened preterm labor in three hospitalization units (Units A, B and C). In the first phase of the study (observational), cervical length was measured by transvaginal ultrasound, but managing physicians were blinded to the results. In the second phase (interventional), physicians from Unit A remained blinded to cervical length information, but Units B and C incorporated these data into their clinical management protocols. Early discharge was contemplated if the cervix measured 25 mm or more on admission (Unit B) or no changes were observed over 48 h (Unit C). Duration of hospital stay and delivery rates within 7 days and before 37 weeks' gestation were recorded.

RESULTS

Hospital stay was significantly reduced in Units B and C in the interventional phase, while no changes were observed in Unit A. Delivery rates within 7 days and before 37 weeks' gestation were similar in the three units during the two stages of the study.

CONCLUSION

Routine use of ultrasound cervical length assessment in patients admitted with threatened preterm labor may reduce the duration of hospital stay without increasing the rate of preterm births. These data should be confirmed by means of an appropriately designed randomized clinical trial.

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.

Preventing low birth weight: is prenatal care the answer?

OBJECTIVES

To review the evidence of effectiveness of prenatal care for preventing low birth weight (LBW).

METHODS

We reviewed original research, systematic reviews, meta-analyses and commentaries for evidence of effectiveness of the three core components of prenatal care--risk assessment, health promotion and medical and psychosocial interventions--for preventing the two constituents of LBW: preterm birth and intrauterine growth restriction (IUGR).

RESULTS

Clinical risk assessment will fail to identify the majority of pregnancies at risk for preterm delivery or IUGR. While biophysical and biochemical modalities appear promising, their cost-effectiveness has not been demonstrated, nor can their routine use be recommended in the absence of effective interventions. Smoking cessation programs appear to be modestly effective. There is insufficient evidence to conclude a benefit for nutrition interventions, work counseling or preterm birth education. Only antenatal corticosteroid therapy has demonstrated a clear benefit in the tertiary prevention of preterm delivery. Interventions for which there is insufficient evidence to conclude a benefit include bed rest, hydration, sedation, cerclage, progesterone supplementation, antibiotic treatment, tocolysis without concomitant use of corticosteroids, thyrotropin-releasing hormone, psychosocial support and home visitation. Additionally, there is a paucity of evidence supporting the effectiveness of prenatal interventions, such as low-dose aspirin, bed rest, maternal hyperoxygenation, plasma volume expansion and antenatal fetal assessment, in preventing IUGR or its associated morbidity and mortality.

CONCLUSIONS

Neither preterm birth nor IUGR can be effectively prevented by prenatal care in its present form. Preventing LBW will require reconceptualization of prenatal care as part of a longitudinally and contextually integrated strategy to promote optimal development of women's reproductive health not only during pregnancy, but over the life course.

Approaches to heterogeneity in meta-analysis

This paper reviews publications from January 1999 to March 2001 on reproductive health topics that were self-identified as meta-analysis or were indexed as meta-analysis in MEDLINE. It sought to assess whether tests of statistical heterogeneity were done, whether the results were reported, and how a finding of significance for a test of statistical heterogeneity was handled and the results interpreted. The review identified some concerns. Tests of statistical heterogeneity were not done universally even though virtually all writers on the topic emphasize their importance. Even when done, results of these tests were not universally reported. Although the consensus appears to be that heterogeneity tests are conservative for meta-analysis of studies and a probability value of 0.10 is preferred, many meta-analyses used the conventional value of 0.05 without providing a reason. The rationale for the choice of a random or fixed effects model was not generally evident. The review also provided some positive models and some recommendations for assessing, reporting and exploring heterogeneity are made considering these models and the published recommendations of experts.

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

OBJECTIVE

The aim of this study was to examine the relation between cervical length and the presence of funneling and the risk of preterm delivery.

METHOD

This prospective blind cohort involved 200 hospitalized women with preterm labor in a tertiary care hospital. Women were recruited for a single transvaginal ultrasonography to assess cervical length and presence of funneling. The main outcome measures were: (1) relative risks (RR) and adjusted odds ratios of preterm delivery (<37 weeks' gestation); (2) time interval between the cervical ultrasonography date to 37 weeks' gestation or to-preterm birth.

RESULTS

The RR of preterm delivery according to the cervical length (cut-off of <30 mm) was 2.79 (95% CI 1.70--4.59). The RR according to the presence of funneling (cut-off of >5 mm) was 1.39 (95% CI 0.99--1.95). The adjusted odds ratio was 3.92 (95% IC 1.75--8.75) for cervical length and 0.77 (95% CI 0.35--1.67) for funneling. Women with a cervical length of <30 mm had a significantly shorter interval from ultrasonography date up to 37 weeks' gestation than did women with a cervical length of >30 mm (P<0.003).

CONCLUSION

Ultrasonographic mensuration of the cervix provides predictive information on the risk of preterm delivery.