Rates of recurrent preterm birth by obstetrical history and cervical length

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 Grey (unpublished) literature was identified through searching the websites of health technology assessment agencies, clinical practice guideline collections, clinical trial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 Assessment for Predicting Preterm Birth-Cervical Length and Beyond

Preterm birth is considered one of the main etiologies of neonatal death, as well as short- and long-term disability worldwide. A number of pathophysiological processes take place in the final unifying factor of cervical modifications that leads to preterm birth. In women at high risk for preterm birth, cervical assessment is commonly used for prediction and further risk stratification. This review outlines the rationale for cervical length screening for preterm birth prediction in different clinical settings within existing and evolving new technologies to assess cervical remodeling.

Spontaneous preterm birth and cervical length in a pregnant Asian population

Objective

Preterm birth (birth before 37 weeks of completed gestation) is the leading cause of neonatal death, and has an incidence of 5–13% which is believed to be on the rise. The objective of this study was to determine the rate of spontaneous preterm birth and investigate the relationship between preterm birth and cervical length in a pregnant Asian population.

Materials and methods

A prospective observational study between September 2010 and November 2013 was performed at KK Women’s and Children’s Hospital, Singapore. 1013 women with single viable pregnancies were recruited at less than 14 weeks of gestation between September 2010 and November 2013, excluding those with multiple gestation, pre-existing autoimmune or renal disease or those with current pregnancies complicated by aneuploidy or fetal anomalies. Participant characteristics were obtained from an interviewer-administered questionnaire at the first recruitment visit. Cervical length was measured using ultrasound at each of the 4 antenatal visits (Visit 1: < 14 weeks, Visit 2: 18–22 weeks, Visit 3: 28–32 weeks and Visit 4: > 34 weeks) using the Fetal Medicine Foundation protocol. Data on pregnancy outcomes were obtained from obstetric case notes and records. The main outcome measure examined in this study was that of spontaneous preterm birth and its relationship to cervical length.

Results

There was a significantly shorter cervical length both in the 2nd trimester (18 to 22 weeks) and the 3rd trimester (28 to 32 weeks) in the preterm birth group compared to the term birth group (p = 0.028 and p < 0.001 respectively). In the first trimester (11 to 14 weeks), there was no statistically significant difference in cervical length between the two groups (p = 0.425). ROC curve analysis for cervical length in the preterm birth group for 18 to 22 weeks and 28 to 32 weeks showed an AUC of 0.605 and 0.725 respectively. At 28 to 32 weeks of gestation, a cut-off level at 2.49 cm has a sensitivity of 54.8%, specificity of 82.5%, negative predictive value of 97.9% and positive predictive value of 11.1%.

Conclusion

There is a significantly shorter cervical length in the 2nd and 3rd trimester in the preterm birth group. Cervical length is a moderate predictor of preterm birth with good negative predictive value and a relatively good specificity. Ultrasound cervical length screening for pregnant Asian women between 18 and 22 weeks of gestation with a cutoff of ≥ 2.48cm can help to identify a group of women who are at risk for preterm birth.

Preterm birth: seven-year retrospective study in a single centre population

Background

Preterm birth is a health and social problem, considered the leading cause of neonatal mortality worldwide. It is associated with higher rates of neurodevelopmental morbidity, sensorineural impairments and other complications. The aim of the study was to describe the incidence and the major risk factors associated with preterm birth.

Methods

We performed a single center, observational and retrospective Cohort study in the Division of Obstetrics and Gynaecology, University Hospital “G. Martino”, Messina. Clinical records of all pregnant women who delivered from 1st January 2010 to 31 of December 2016 were collected.

Results

In the 7 years considered, a total of 7954 pregnant women were included in our study. The majority of all preterm births were due to infants born late preterm (71.83%), 26.45% were due to preterm and 1.72% to extremely preterm. The preterm cohort had a higher proportion of history of preterm delivery (p < 0.0001), and unmarried (p = 0.003) and underweight or obese patients (p < 0.0001). In addition, prematurity was associated with presence of uterine anomalies (p < 0.0001), vaginal/urinary infections (p = 0.02), poli/oligohydramnios (p < 0.0001), maternal diabetes (p = 0.004), hypertension (p < 0.0001), short cervical length (p < 0.0001).

Conclusions

We suggest prompt identification of all risk factors associated with preterm birth to apply immediate and appropriate specific interventions.

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.

The cytokine network in women with an asymptomatic short cervix and the risk of preterm delivery

PROBLEM

To characterize the amniotic fluid (AF) inflammatory-related protein (IRP) network in patients with a sonographic short cervix (SCx) and to determine its relation to early preterm delivery (ePTD).

METHOD OF STUDY

A retrospective cohort study included women with a SCx (≤25 mm; n=223) who had amniocentesis and were classified according to gestational age (GA) at diagnosis and delivery (ePTD <32 weeks of gestation).

RESULTS

(i) In women with a SCx ≤ 22 1/7 weeks, the concentration of most IRPs increased as the cervix shortened; those with ePTD had a higher rate of increase in MIP-1α, MCP-1, and IL-6 concentrations than those delivering later; and (ii) the concentration of most IRPs and the correlation between several IRP pairs were higher in the ePTD group than for those delivering later.

CONCLUSION

Women with a SCx at 16-22 1/7 weeks have a unique AF cytokine network that correlates with cervical length at diagnosis and GA at delivery. This network may aid in predicting ePTD.

Sterile intra-amniotic inflammation in asymptomatic patients with a sonographic short cervix: prevalence and clinical significance

OBJECTIVE

To determine the frequency and clinical significance of sterile and microbial-associated intra-amniotic inflammation in asymptomatic patients with a sonographic short cervix.

METHODS

Amniotic fluid (AF) samples obtained by transabdominal amniocentesis from 231 asymptomatic women with a sonographic short cervix [cervical length (CL) ≤25 mm] were analyzed using cultivation techniques (for aerobic and anaerobic as well as genital mycoplasmas) and broad-range polymerase chain reaction (PCR) coupled with electrospray ionization mass spectrometry (PCR/ESI-MS). The frequency and magnitude of intra-amniotic inflammation [defined as an AF interleukin (IL)-6 concentration ≥2.6 ng/mL], acute histologic placental inflammation, spontaneous preterm delivery (sPTD), and the amniocentesis-to-delivery interval were examined according to the results of AF cultures, PCR/ESI-MS and AF IL-6 concentrations.

RESULTS

Ten percent (24/231) of patients with a sonographic short cervix had sterile intra-amniotic inflammation (an elevated AF IL-6 concentration without evidence of microorganisms using cultivation and molecular methods). Sterile intra-amniotic inflammation was significantly more frequent than microbial-associated intra-amniotic inflammation [10.4% (24/231) versus 2.2% (5/231); p < 0.001]. Patients with sterile intra-amniotic inflammation had a significantly higher rate of sPTD <34 weeks of gestation [70.8% (17/24) versus 31.6% (55/174); p < 0.001] and a significantly shorter amniocentesis-to-delivery interval than patients without intra-amniotic inflammation [median 35, (IQR: 10-70) versus median 71, (IQR: 47-98) days, (p < 0.0001)].

CONCLUSION

Sterile intra-amniotic inflammation is more common than microbial-associated intra-amniotic inflammation in asymptomatic women with a sonographic short cervix, and is associated with increased risk of sPTD (<34 weeks). Further investigation is required to determine the causes of sterile intra-amniotic inflammation and the mechanisms whereby this condition is associated with a short cervix and sPTD.

Cervical strain determined by ultrasound elastography and its association with spontaneous preterm delivery

OBJECTIVE

To determine if there is an association between cervical strain, evaluated using ultrasound elastography, and spontaneous preterm delivery (sPTD) <37 weeks of gestation.

METHODS

One hundred and eighty nine (189) women at 16-24 weeks of gestation were evaluated. Ultrasound elastography was used to estimate cervical strain in three anatomical planes: one mid-sagittal in the same plane used for cervical length measurement, and two cross sectional images: one at the level of the internal cervical os, and the other at the level of the external cervical os. In each plane, two regions of interest (endocervix and entire cervix) were examined; a total of six regions of interest were evaluated.

RESULTS

The prevalence of sPTD was 11% (21/189). Strain values from each of the six cervical regions correlated weakly with cervical length (from r=-0.24, P<0.001 to r=-0.03, P=0.69). Strain measurements obtained in a cross sectional view of the internal cervical os were significantly associated with sPTD. Women with strain values ≤25th centile in the endocervical canal (0.19) and in the entire cervix (0.14) were 80% less likely to have a sPTD than women with strain values >25th centile [endocervical: odds ratio (OR) 0.2; 95% confidence interval (CI), 0.03-0.96; entire cervix: OR 0.17; 95% CI, 0.03-0.9]. Additional adjustment for gestational age, race, smoking status, parity, maternal age, pre-pregnancy body mass index, and previous preterm delivery did not appreciably alter the magnitude or statistical significance of these associations. Strain values obtained from the external cervical os and from the sagittal view were not associated with sPTD.

CONCLUSION

Low strain values in the internal cervical os were associated with a significantly lower risk of spontaneous preterm delivery <37 weeks of gestation.

The utility of screening for historical risk factors for preterm birth in women with known second trimester cervical length

OBJECTIVE

To evaluate for the presence of risk factors (RFs) for preterm birth (PTB) in women without prior PTB having second trimester cervical length (CL) screening, and to estimate the utility of RF screening.

METHODS

"Low-risk" singletons were prospectively screened with midtrimester transvaginal ultrasound CL. Prior PTB, intrauterine fetal demise and lethal anomalies were excluded. Women were analyzed based on second trimester CL (<25 mm versus ≥25 mm) and the presence of RFs for PTB. A p-value of < 0.05 was considered significant.

RESULTS

A total of 639 women were screened; 8% had CL <25 mm. Ninety-eight percent of women with CL <25 mm and 95% of women with CL ≥25 mm had RFs for PTB. Five percent of women with a CL ≥25 mm delivered preterm as compared to 18% with CL <25 mm (p < 0.01). Treatment of cervical dysplasia, drug use during the pregnancy and unmarried status were significantly more common in women with CL <25 mm than CL ≥25 mm. When data were analyzed by CL, the presence of additional RFs did not add to the prediction of PTB <37 weeks.

DISCUSSION

Over 95% of singleton gestations without prior PTB have ≥1 other RF for PTB. In women without prior PTB, assessment of other PTB RFs does not add to prediction of PTB provided by CL alone.

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.

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.

Transvaginal ultrasonographic measurement of cervical length in asymptomatic high-risk women with a short cervical length in the previous pregnancy

OBJECTIVE

To determine if asymptomatic women at high risk of preterm delivery who had a short cervical length in their previous pregnancy and delivered at term are at increased risk of having a short cervical length in their next pregnancy, and whether they are at increased risk of preterm birth.

METHODS

This retrospective cohort study included high-risk (those with a history of spontaneous preterm birth, uterine anomaly or excisional treatment for cervical dysplasia) asymptomatic women who were pregnant with a singleton gestation delivering between April 2003 and March 2010, who had had a previous pregnancy and who had transvaginal ultrasonographic cervical length measurement performed at 16-30 weeks' gestation in both pregnancies. Comparison was among women who had a short cervical length (< 3.0 cm) in their previous pregnancy but delivered at term in that pregnancy (Short Term Group), women with a history of a normal cervical length (≥ 3.0 cm) in their previous pregnancy delivering at term (Long Term Group), and women who had a short cervical length (< 3.0 cm) in their previous pregnancy delivering preterm (Short Preterm Group). Primary outcomes were spontaneous preterm birth at < 37 weeks' gestation and cervical length. Secondary outcomes were spontaneous preterm birth at < 35 weeks and < 32 weeks, low birth weight, maternal outcomes and neonatal morbidity.

RESULTS

A total of 62 women were included. Women in the Short Term Group were more likely to have a short cervical length in their next pregnancy compared with those in the Long Term Group (10/23 (43.5%) vs. 4/26 (15.4%), respectively) but not as likely as women in the Short Preterm Group (9/13 (69.2%); P=0.003). Women in the Short Term Group were not at an increased risk of spontaneous preterm birth at < 37 weeks in the next pregnancy compared with women in the Long Term Group (2/23 (8.7%) vs. 2/26 (7.7%), respectively), but women in the Short Preterm Group were at an increased risk (6/13 (46.2%); P<0.0001). Compared with women in the Short Term and Long Term groups, women in the Short Preterm Group were also at an increased risk of threatened preterm labor (6/23 (26.1%) and 4/26 (15.4%) vs. 9/13 (69.2%), respectively; P=0.002) and of receiving corticosteroids for fetal lung maturation (6/23 (26.1%) and 4/26 (15.4%) vs. 11/13 (84.6%), respectively; P<0.0001).

CONCLUSION

Although high-risk asymptomatic women with a short cervical length in their previous pregnancy who delivered at term are at increased risk of having a short cervix in their next pregnancy, they are not at increased risk of preterm birth.

Follow-up cervical length in asymptomatic high-risk women and the risk of spontaneous preterm birth

OBJECTIVE

To determine whether further cervical length shortening by transvaginal ultrasonography in asymptomatic high-risk women with a short cervical length adds additional predictive value for spontaneous preterm birth and perinatal morbidity.

STUDY DESIGN

Women with a history of spontaneous preterm birth, loop electrosurgical excision procedure, cone biopsy or uterine anomaly, who were pregnant with singleton gestations and were found by transvaginal ultrasonography to have a cervical length <3.0 cm at 20 to 28 weeks' gestation, and who underwent a follow-up cervical length within 3 weeks were evaluated, comparing those with further cervical length shortening (>10%) to those without further shortening. Primary outcomes were spontaneous preterm birth <35 weeks' gestation and perinatal morbidity. Secondary outcomes included spontaneous preterm birth <37 weeks, <34 weeks, <32 weeks, birth weight <2500 g, maternal and other neonatal outcomes.

RESULT

Compared with women without further cervical shortening, those with further shortening were found by univariate analyses to have higher rates of spontaneous preterm birth <35 weeks (34.8 versus 8.5%, P = 0.014), <37 weeks (56.5 versus 21.3%, P = 0.003), <34 weeks (30.4 versus 2.1%, P = 0.001), <32 weeks (21.7 versus 0%, P = 0.003), birth weight <2500 g (60.9 versus 17.0%, P<0.0001), neonatal intensive care unit admission (47.8 versus 17.0%, P = 0.006) and composite perinatal morbidity (43.5 versus 14.9%, P = 0.009). Logistic regression revealed the only independent predictors of spontaneous preterm birth <35 weeks were further cervical length shortening (adjusted odds ratio (aOR) 5.73; 95% confidence interval (CI) 1.31 to 24.43) and gestational age at short cervical length (aOR 0.95; 95% CI 0.91 to 0.99).

CONCLUSION

Further cervical length shortening in asymptomatic high-risk women with a short cervical length is an important independent predictor of spontaneous preterm birth <35 weeks and perinatal morbidity.

All Our Babies Cohort Study: recruitment of a cohort to predict women at risk of preterm birth through the examination of gene expression profiles and the environment

Background

Preterm birth is the leading cause of perinatal morbidity and mortality. Risk factors for preterm birth include a personal or familial history of preterm delivery, ethnicity and low socioeconomic status yet the ability to predict preterm delivery before the onset of preterm labour evades clinical practice. Evidence suggests that genetics may play a role in the multi-factorial pathophysiology of preterm birth. The All Our Babies Study is an on-going community based longitudinal cohort study that was designed to establish a cohort of women to investigate how a women's genetics and environment contribute to the pathophysiology of preterm birth. Specifically this study will examine the predictive potential of maternal leukocytes for predicting preterm birth in non-labouring women through the examination of gene expression profiles and gene-environment interactions.

Methods/Design

Collaborations have been established between clinical lab services, the provincial health service provider and researchers to create an interdisciplinary study design for the All Our Babies Study. A birth cohort of 2000 women has been established to address this research question. Women provide informed consent for blood sample collection, linkage to medical records and complete questionnaires related to prenatal health, service utilization, social support, emotional and physical health, demographics, and breast and infant feeding. Maternal blood samples are collected in PAXgene™ RNA tubes between 18-22 and 28-32 weeks gestation for transcriptomic analyses.

Discussion

The All Our Babies Study is an example of how investment in clinical-academic-community partnerships can improve research efficiency and accelerate the recruitment and data collection phases of a study. Establishing these partnerships during the study design phase and maintaining these relationships through the duration of the study provides the unique opportunity to investigate the multi-causal factors of preterm birth. The overall All Our Babies Study results can potentially lead to healthier pregnancies, mothers, infants and children.

Second trimester cervical length and risk of preterm birth in women with twin gestations treated with 17-α hydroxyprogesterone caproate

OBJECTIVE

To compare rates of preterm birth before 35 weeks based on cervical length measurement at 16-20 weeks in women with twin gestations who received 17-α hydroxyprogesterone caproate (17OHPC) or placebo.

METHODS

This is a secondary analysis of a randomised, double-blind, placebo-controlled trial of twin gestations exposed to 17OHPC or placebo. Baseline transvaginal ultrasound evaluation of cervical length was performed prior to treatment assignment at 16-20 weeks. Cervical length measurements were categorised according to the 10th, 25th, 50th and 75th percentiles in the women studied. The effect of 17OHPC administration in women with a short (25th percentile) and long (75th percentile) cervix was evaluated.

RESULTS

Of 661 twin gestations studied, 221 (33.4%) women enrolled at 11 centers underwent cervical length measurement. The 10th, 25th, 50th, 75th percentiles for cervical length at 16-20 weeks were 32, 36, 40 and 44 mm, respectively. The risk of preterm birth <35 weeks was increased in women with a cervical length <25th percentile (55.8 vs. 36.9%, p=0.02). However, a cervical length >75th percentile at this gestational age interval was not protective for preterm birth (36.5 vs. 42.9%, p=0.42). Administration of 17OHPC did not reduce preterm birth before 35 weeks among those with either a short or a long cervix (64.3 vs. 45.8%, p=0.18 and 38.1 vs. 35.5%, p=0.85, respectively).

CONCLUSION

Women with twin gestations and a cervical length below the 25th percentile at 16-20 weeks had higher rates of preterm birth. In this subgroup of women, 17 OHPC did not prevent preterm birth before 35 weeks gestation. A cervical length above the 75th percentile at 16-20 weeks did not significantly reduce the risk of preterm birth in this high risk population.

The risk of impending preterm delivery in asymptomatic patients with a nonmeasurable cervical length in the second trimester

OBJECTIVE

The purpose of this study was to determine the pregnancy outcome of asymptomatic patients in the second trimester with a nonmeasurable cervical length (0 mm).

STUDY DESIGN

This retrospective cohort study included 78 patients with singleton pregnancies and a sonographic nonmeasurable cervix that was detected at 14-28 weeks of gestation. Patients with cervical cerclage were excluded.

RESULTS

We found that (1) 75.3% of the patients delivered before 32 weeks of gestation; (2) the median diagnosis-to-delivery interval was 20.5 days, and the delivery rate within 7 and 14 days was 28.2% and 35.6%, respectively; and (3) patients with a nonmeasurable cervix that was diagnosed at <24 weeks of gestation had a shorter median diagnosis-to-delivery interval than patients who were diagnosed at 24-28 weeks of gestation (17.5 vs 41 days; P = .009).

CONCLUSION

Asymptomatic women with a nonmeasurable cervix in the second trimester have a median diagnosis-to-delivery interval of approximately 3 weeks. Almost 65% of these patients will not deliver within 2 weeks, yet 75% of them will deliver before 32 weeks of gestation. The earlier a nonmeasurable cervix is identified, the shorter the diagnosis-to-delivery interval.

Clinical significance of early (< 20 weeks) vs. late (20-24 weeks) detection of sonographic short cervix in asymptomatic women in the mid-trimester

OBJECTIVE

The aim of this study was to determine whether the risk of early spontaneous preterm delivery (PTD) in asymptomatic women with a sonographic cervical length of ≤ 15 mm in the mid-trimester changes as a function of gestational age at diagnosis.

METHODS

This cohort study included 109 asymptomatic patients with a sonographic cervical length of ≤ 15 mm diagnosed at 14-24 weeks of gestation. Women with a multifetal gestation, cerclage and a cervical dilatation of > 2 cm were excluded. The study population was stratified by gestational age at diagnosis (< 20 weeks vs. 20-24 weeks) and by cervical length (≤ 10 mm vs. 11-15 mm). The primary outcome variables were PTD at < 28 and < 32 weeks of gestation and the diagnosis-to-delivery interval.

RESULTS

The median gestational age at diagnosis of a short cervix before 20 weeks and at 20-24 weeks was 18.9 and 22.7 weeks, respectively. Women diagnosed before 20 weeks had a higher rate of PTD at < 28 weeks (76.9% vs. 30.9%; P < 0.001) and at < 32 weeks (80.8% vs. 48.1%; P = 0.004), and a shorter median diagnosis-to-delivery interval (21 vs. 61.5 days, P = 0.003) than those diagnosed at 20-24 weeks. The rate of amniotic fluid sludge was higher among patients diagnosed with a short cervix at < 20 weeks of gestation than in those in whom it was diagnosed between 20 and 24 weeks (92.3% vs. 48.2%; P < 0.001).

CONCLUSIONS

Asymptomatic women with a sonographic cervical length of ≤ 15 mm diagnosed before 20 weeks of gestation have a dramatic and significantly higher risk of early preterm delivery than women diagnosed at 20-24 weeks. These findings can be helpful to physicians in counseling these patients, and may suggest different mechanisms of disease leading to a sonographic short cervix before or after 20 weeks of gestation.

Mid-trimester cervical inflammatory milieu and sonographic cervical length

OBJECTIVE

The purpose of this study was to explore the relation between the relative balance of pro- and antiinflammatory cytokines in cervical fluid and mid-trimester cervical length.

STUDY DESIGN

In this prospective longitudinal cohort of women with a previous spontaneous preterm birth, mid-trimester cervical length ultrasound scans and cervical fluid levels were obtained serially. Multiple pro- and antiinflammatory cytokines were selected. We summed the multiples of the median for proinflammatory cytokines to generate the proinflammatory and the antiinflammatory scores. The relation between cervical length and pro-/antiinflammatory ratio was assessed by generalized estimating equations.

RESULTS

The pro-/antiinflammatory ratio had a negative linear association with cervical length (beta = -0.09; P < .001). Sixty percent of visits demonstrated greater concentrations of proinflammatory cytokines relative to antiinflammatory cytokines. This relationship did not change between first and last visits.

CONCLUSION

Among women with a previous preterm birth, shorter mid-trimester cervical length is associated with a more proinflammatory balance of cytokines in the cervical inflammatory milieu.

Care for women with prior preterm birth

Women who have delivered an infant between 16 and 36 weeks' gestation have an increased risk of preterm birth in subsequent pregnancies. The risk increases with more than 1 preterm birth and is inversely proportional to the gestational age of the previous preterm birth. African American women have rates of recurrent preterm birth that are nearly twice that of women of other backgrounds. An approximate risk of recurrent preterm birth can be estimated by a comprehensive reproductive history, with emphasis on maternal race, the number and gestational age of prior births, and the sequence of events preceding the index preterm birth. Interventions including smoking cessation, eradication of asymptomatic bacteriuria, progestational agents, and cervical cerclage can reduce the risk of recurrent preterm birth when employed appropriately.

The effect of treatment with 17 alpha-hydroxyprogesterone caproate on changes in cervical length over time

OBJECTIVE

The purpose of this study was to examine whether women who were treated with 17 alpha-hydroxyprogesterone caproate (17-OHPC) to prevent recurrent preterm birth experienced a change in cervical shortening over time, compared with women who were not treated.

STUDY DESIGN

We conducted a retrospective exposure cohort study of women who were enrolled in a prematurity prevention clinic from 1999-2008 with a singleton pregnancy with > or =1 previous spontaneous preterm births (<37 weeks of gestation) who underwent > or =2 cervical length measurements by endovaginal ultrasound.

RESULTS

Of 200 women, 105 women received treatment with 17-OHPC; 95 women did not. Women who were treated with 17-OHPC were more likely to have experienced a previous preterm birth (26.0 vs 27.8 weeks; P = .01) than those who were not treated with 17-OHPC. There was no difference in the average weekly change in cervical length among women treated with 17-OHPC, compared with those who were not, after adjustment for covariates (0.79 mm/week; 95% confidence interval, -1.18 to 2.76).

CONCLUSION

There was no difference in the average weekly change in cervical length measurements over time in women who underwent 17-OHPC treatment, compared with those who were not treated.

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.

Prediction and Prevention of Recurrent Spontaneous Preterm Birth

Rates of preterm birth have continued to rise despite intensive research efforts over the last several decades. A woman who has a spontaneous preterm birth is at high risk for a subsequent preterm birth. Studies have identified clinical, sonographic, and biochemical markers that help to identify the women at highest risk. Determining cervical length and measuring cervicovaginal fibronectin have been proposed as useful tools for evaluating women at risk of preterm birth and may identify those who might benefit from a timely course of antenatal corticosteroids, but effective interventions to prevent preterm birth remain elusive. In the prevention of recurrent spontaneous preterm birth, recent trials have confirmed the use of progesterone beginning in the second trimester as an effective intervention. Optimal management of women with a history of spontaneous preterm birth includes a thorough review of the obstetric, medical, and social history, with attention to potentially reversible causes of preterm birth (eg, smoking cessation, acute infections, strenuous activities), accurate ultrasound dating, consideration of progesterone therapy beginning at 16-20 weeks of gestation, and close surveillance during the pregnancy for evolving findings. Results from the ongoing trials of cerclage as an interventional therapy and omega-3 fatty acid supplementation as a preventive therapy will provide additional knowledge for the optimal management of these high-risk women.

Recurrent preterm birth

Recurrent preterm birth is frequently defined as two or more deliveries before 37 completed weeks of gestation. The recurrence rate varies as a function of the antecedent for preterm birth: spontaneous versus indicated. Spontaneous preterm birth is the result of either preterm labor with intact membranes or preterm prelabor rupture of the membranes. This article reviews the body of literature describing the risk of recurrence of spontaneous and indicated preterm birth. Also discussed are the factors which modify the risk for recurrent spontaneous preterm birth (a short sonographic cervical length and a positive cervicovaginal fetal fibronectin test). Patients with a history of an indicated preterm birth are at risk not only for recurrence of this subtype, but also for spontaneous preterm birth. Individuals of black origin have a higher rate of recurrent preterm birth.

Inpatient management for a shortened cervix: who is really at risk?

OBJECTIVE

The objective of the study was to identify risk factors associated with spontaneous preterm delivery (SPD) within 2 weeks of admission in patients with a shortened cervix.

STUDY DESIGN

We reviewed records of patients hospitalized in 2003-2004 with a cervix of 25 mm or less at less than 32 weeks' gestation. The primary outcome was SPD 2 weeks or less of admission.

RESULTS

Sixty-six patients met inclusion criteria. Twelve delivered at 2 weeks or less of admission. There were no differences in maternal and gestational age at admission, history of SPD, and rate of multifetal pregnancy. Those with cervical length (CL) of 5 mm or less were more likely to deliver within 2 weeks than those with CLs 6-25 mm (50% vs 12.5%; P = .01). Logistic regression identified CL less than 5 mm as the only independent predictor of delivery within 2 weeks of admission (P = .01).

CONCLUSION

CL of less than 5 mm in patients at less than 32 weeks' gestation is associated with a high rate of SPD within 2 weeks of diagnosis.

PREMATURE CERVICAL CHANGE AND THE USE OF CERVICAL CERCLAGE

Preterm birth and its subsequent consequences continue to be a major challenge worldwide. In the United States in 2004, 12.5% of infants were born preterm, making the annual societal economic burden associated with preterm birth in excess of $26.2 billion (and this is a modest estimate). Spontaneous preterm birth accounts for about 75% of all preterm births; however, at earlier gestations iatrogenic preterm birth accounts for a greater proportion of all preterm births; at 27–28 weeks 50% are iatrogenic. The proportion of babies transferred to the neonatal unit is more than 90% for those born before 33 completed weeks of gestation compared with 31% at 36 weeks; delivery between 33 completed weeks and 36 completed weeks has a relatively low morbidity and mortality. Nonetheless, 1 in 3 children born preterm but beyond 32 weeks have educational and behavioural problems at the age of 7, with 1 in 4 children born between 32 and 35 weeks requiring support from non-teaching assistants at school. Although more than 40% of babies at 35 completed weeks show signs of maturity, some still need ventilation at 38 completed weeks. Almost one-fifth of all infants born at less than 32 weeks gestation do not survive the first year of life.