Transvaginal sonographic examination of the cervix in asymptomatic pregnant women: review of the literature

A hierarchical procedure to select intrauterine and extrauterine factors for methodological validation of preterm birth risk estimation

Background

Etiopathogenesis of preterm birth (PTB) is multifactorial, with a universe of risk factors interplaying between the mother and the environment. It is of utmost importance to identify the most informative factors in order to estimate the degree of PTB risk and trace an individualized profile. The aims of the present study were: 1) to identify all acknowledged risk factors for PTB and to select the most informative ones for defining an accurate model of risk prediction; 2) to verify predictive accuracy of the model and 3) to identify group profiles according to the degree of PTB risk based on the most informative factors.

Methods

The Maternal Frailty Inventory (MaFra) was created based on a systematic review of the literature including 174 identified intrauterine (IU) and extrauterine (EU) factors. A sample of 111 pregnant women previously categorized in low or high risk for PTB below 37 weeks, according to ACOG guidelines, underwent the MaFra Inventory. First, univariate logistic regression enabled p-value ordering and the Akaike Information Criterion (AIC) selected the model including the most informative MaFra factors. Second, random forest classifier verified the overall predictive accuracy of the model. Third, fuzzy c-means clustering assigned group membership based on the most informative MaFra factors.

Results

The most informative and parsimonious model selected through AIC included Placenta Previa, Pregnancy Induced Hypertension, Antibiotics, Cervix Length, Physical Exercise, Fetal Growth, Maternal Anxiety, Preeclampsia, Antihypertensives. The random forest classifier including only the most informative IU and EU factors achieved an overall accuracy of 81.08% and an AUC of 0.8122. The cluster analysis identified three groups of typical pregnant women, profiled on the basis of the most informative IU and EU risk factors from a lower to a higher degree of PTB risk, which paralleled time of birth delivery.

Conclusions

This study establishes a generalized methodology for building-up an evidence-based holistic risk assessment for PTB to be used in clinical practice. Relevant and essential factors were selected and were able to provide an accurate estimation of degree of PTB risk based on the most informative constellation of IU and EU factors.

Supplementary Information

The online version contains supplementary material available at (10.1186/s12884-021-03654-3).

Cervical length measurement in nulliparous women at term by ultrasound & its relationship to spontaneous onset of labour

Background & objectives:

Data on serial cervical length (CL) measurements in pregnancy at term to predict spontaneous labour onset are scarce and conflicting. This study was conducted to observe CL changes preceding spontaneous onset of labour, by serial transvaginal sonography (TVS) and transabdominal sonography (TAS), in nulliparous Indian women near term.

Methods:

Only nulliparous women with a singleton foetus in cephalic presentation and who confirmed their gestational age were recruited. Sonographic CL measurements were taken at weekly intervals from 36 wk gestation onwards by a single ultrasonologist. Transabdominal and transvaginal measurements were undertaken using the suitable transducer probes with the women in the supine position.

Results:

A total of 104 women with spontaneous onset of labour were evaluated. There was substantial variation in CL measurements, both by TVS and by TAS, from 36 to 40 wk gestation, although the two sets of measurements correlated closely. Mean CL changed significantly over the last three weeks before delivery. However, only one-third of the women showed CL change of >5 mm per week in the last three weeks. There was poor correlation between gestational age at delivery and the last measured CL, either by TVS or TAS. Length >3.1 mm, measured by TVS at 38 wk gestation, predicted post-dated pregnancy to a limited extent.

Interpretation & conclusions:

Inter-individual variations in CL and in CL changes were large. Thus, it was not practical to predict spontaneous onset of labour by sonographic CL measurement near term. Post-dated pregnancy may be predicted with limited success. Further studies should explore other parameters, in addition to CL.

[Is universal screening for cervical length among singleton pregnancies with no history of preterm birth justified?]

The ultrasonographic measurement of cervical length with a cutoff of 15mm is currently the best method to identify a group of asymptomatic women in the general population at risk of spontaneous preterm birth, especially among asymptomatic patients with a singleton pregnancy with no history of preterm birth. Cerclage and 17 alpha-hydroxyprogesterone caproate (17OHP-C) are ineffective to reduce the risk of preterm birth among asymptomatic patients with a short cervix in midtrimester. However, vaginal progesterone (200-mg capsules of micronized progesterone or gel containing 90mg progesterone) has been demonstrated effective in 2 large randomized trials to reduce the risk of preterm birth and possibly the composite morbidity and perinatal mortality associated among asymptomatic women with a short cervix in the general population screened by ultrasound of the cervix in midtrimester. Three cost-effectiveness analyses are converging to show that universal screening for cervical length with vaginal progesterone treatment seems to be cost-effective compared with no screening. However, it is too early to definitively conclude that universal screening is justified for several reasons: many women must be screened to prevent a relatively small number of preterm births. Moreover, the epidemiology of preterm delivery is such that the use of progesterone in asymptomatic women with a short cervix screened by ultrasound in midtrimester in the general population will not significantly reduce the prevalence of preterm births; there are no data comparing the effectiveness of universal ultrasound screening followed by vaginal progesterone treatment in case of short cervix versus no universal screening associated to a progesterone treatment in case of incidentally observed short cervix; the universal ultrasound screening may not produce the same results in practice than those observed in published randomized trials, due to population differences, "indication creep", or "stretching of the cutoff" defining the short cervix. Moreover, the implementation of unevaluated or not recommended treatments, such as bed rest, tocolytics, 17OHP-C or cerclage, can potentially cause unintended deleterious consequences and reduce the cost-effectiveness; the cost-effectiveness analyses evaluating universal screening for cervical length present uncertainties on critical variables, notably the short cervix prevalence and the progesterone efficacy. In conclusion, although the implementation of such a screening strategy can be considered by individual practitioners, this screening cannot be universally mandated.

Twin-to-Twin Transfusion Syndrome: Definition, Staging, and Ultrasound Assessment

Objective: The purpose of this article is to review the definition of twin-to-twin transfusion syndrome (TTTS) and the sonographic diagnostic assessment of these cases prior to therapy.

Materials and Methods: The article addresses the terminology used to refer to the condition and describes the systematic ultrasound assessment of the condition, including the ultrasound diagnosis, the staging of the disease, cervical assessment and pre-operative mapping.

Results: From an etymologic and medical point of view, the term ‘fetofetal transfusion’ is more appropriate than ‘TTTS’. However, as the latter, and its attendant acronym TTTS, have been widely adopted in the English language, it is impractical to change at this point. TTTS is defined sonographically in the combined presence of a maximum vertical pocket (MVP) of 8 cm or greater in one sac and 2 cm or less in the other sac, regardless of the gestational age at diagnosis. Staging of the condition using the Quintero staging system is practical, reproducible, and accepted. Transvaginal cervical length assessment should be an integral part of the ultrasound evaluation. Pre-operative mapping to anticipate the location of the placental vascular anastomoses and avoid injuring the dividing membrane is also discussed.

Conclusions: The term ‘TTTS’ can continue to be used in the English medical literature. The condition can be diagnosed and assessed following a systematic ultrasound methodology. The use of such ultrasound methodology breaks the examination into a distinct set of components, assuring a comprehensive examination and proper communication among caregivers.

Correlation Between Cervical Lengths Measured by Transabdominal and Transvaginal Sonography for Predicting Preterm Birth

OBJECTIVES

Cervical length assessment is important for predicting preterm birth. Cervical length measurement using transabdominal sonography is more comfortable for the patient but has more limitations than transvaginal sonography. Our aim was to determine whether transabdominal sonography could identify those women who should undergo transvaginal sonography for prediction of preterm birth.

METHODS

In this prospective study, women underwent cervical length measurements by transabdominal and transvaginal sonography between 20 and 29 gestational weeks and were followed until delivery. We assessed whether short cervical lengths on transabdominal sonography could predict short cervical lengths on transvaginal sonography and whether these measurements could predict preterm births (<34 gestational weeks).

RESULTS

The mean cervical lengths were not significantly different between the techniques (mean ± SD, 3.78 ± 0.82 and 3.82 ± 0.77 cm on transabdominal and transvaginal sonography, respectively; P = .09). The sensitivity of short cervical lengths (<2 cm) on transabdominal sonography for prediction of short cervical lengths on transvaginal sonography was 100%. The sensitivity, specificity, positive predictive value, negative predictive value, and relative risk of short cervical lengths (<2 cm) for predicting preterm birth were 21.4%, 98.68%, 50.00%, 95.32%, and 13.22 when using transabdominal sonography and 28.57%, 94.94%, 66.6%, 95.74%, and 17.78 when using transvaginal sonography, respectively. In an analysis that included cases with transabdominal sonography, the sensitivity of short cervical lengths for predicting preterm birth was increased.

CONCLUSIONS

Women whose cervical lengths are measurable and long on transabdominal sonography may not need transvaginal sonography. Women whose cervical lengths are unmeasurable or short (<2 or <2.5 cm) on transabdominal sonography should undergo transvaginal sonography to measure cervical lengths for prediction of preterm birth.

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.

Relationship between interpregnancy interval and cervical length in high-risk women

OBJECTIVE

Our objective was to evaluate the relationship between the interpregnancy interval (IPI) and next-pregnancy mid-trimester cervical length (CL) in women at high risk for recurrent spontaneous preterm birth (SPTB).

METHODS

Retrospective review identified high-risk women, defined as a prior SPTB <36 weeks, who began scheduled serial transvaginal sonographic CL screening at 16-18 weeks gestation between December 2008 and November 2010. All CL assessment ended by 22(6/7) weeks, and weekly 17-α hydroxyprogesterone caproate, 250 mg IM, was recommended to all patients. Details of the prior and current pregnancy were collected, and regression models were used to evaluate the relationship between IPI and CL shortening.

RESULTS

One hundred and eight women with singleton gestations and a qualifying SPTB underwent CL screening. The mean (SD) birth gestational age (GA) of the last pregnancy was 25 (10) weeks, the median IPI was 613 (range 49-6038) days, and the mean (SD) delivery GA in the current pregnancy was 36 (5.3) weeks. Linear regression found no significant relationship between the IPI and the GA of the current birth (p = 0.98). There was a weak significant relationship between IPI and shortest CL (p = 0.04). However, after controlling for the GA of the prior pregnancy, this relationship was non-significant (p = 0.13).

CONCLUSIONS

IPI does not predict next birth outcome or next-pregnancy mid-trimester CL in high-risk women managed with progesterone and ultrasound-indicated cerclage.

17 alpha-hydroxyprogesterone caproate does not prolong pregnancy or reduce the rate of preterm birth in women at high risk for preterm delivery and a short cervix: a randomized controlled trial

OBJECTIVE

The objective of the study was to evaluate the efficacy of 17 alpha-hydroxyprogesterone caproate (17OHP-C) in prolonging gestation in patients with a short cervix and other risk factors for preterm delivery, such as previous preterm birth, cervical surgery, uterine anomalies, or prenatal diethylstilbestrol (DES) exposure.

STUDY DESIGN

This open-label, multicenter, randomized controlled trial included asymptomatic singleton pregnancies from 20(+0) through 31(+6) weeks of gestation with a cervical length less than 25 mm and a history of preterm delivery or cervical surgery or uterine malformation or prenatal DES exposure. Randomization assigned them to receive (or not) 500 mg of intramuscular 17OHP-C weekly until 36 weeks. The primary outcome was time from randomization to delivery.

RESULTS

After enrolling 105 patients, an interim analysis demonstrated the lack of efficacy of 17OHP-C in prolonging pregnancy. The study was discontinued because of futility. The groups were similar for maternal age, body mass index, parity, gestational age at inclusion, history of uterine anomalies, DES syndrome, previous preterm delivery or midtrimester abortion, and cervical length at randomization. The enrollment-to-delivery interval did not differ between patients allocated to 17OHP-C (n = 51) and those allocated to the control group (n = 54) (median [interquartile range] time to delivery: 77 [54-103] and 74 [52-99] days, respectively). The rate of preterm delivery less than 37 (45% vs 44%, P > .99), less than 34 (24% vs 30%, P = .51), or less than 32 (14% vs 20%, P = .44) weeks was similar in patients allocated to 17OHP-C and those in the control group.

CONCLUSION

17OHP-C did not prolong pregnancy in women with singleton gestations, a sonographic short cervix, and other risk factors of preterm delivery (prior history, uterine malformations, cervical surgery, or prenatal DES exposure).

Prophylactic oral nifedipine to reduce preterm delivery: a randomized controlled trial in women at high risk

OBJECTIVE

To establish the efficacy of prophylactic nifedipine vs. placebo in reducing spontaneous preterm delivery in asymptomatic women at high risk for preterm delivery.

DESIGN

Prospective multicentric randomized double-blind study.

SETTING

Tertiary care centre, University Hospitals of Brescia and Torino, Italy.

POPULATION

Eighty-seven singleton pregnancies without uterine contractions and ultrasonographic cervical length of ≤25 mm at 24-32 weeks, at risk for preterm delivery, with longitudinal follow up in our Preterm Prevention Clinic.

METHODS

Selection was done on the basis of ultrasonographic cervical length; 43 women were randomized to receive placebo and 44 to receive nifedipine.

MAIN OUTCOME MEASURES

Primary end point: spontaneous preterm delivery <37 weeks in nifedipine vs. placebo.

SECONDARY OUTCOMES

delivery <32 weeks, maternal side effects, neonatal complications, admissions to the Neonatal Intensive Care Unit and randomization/delivery time in nifedipine vs. placebo.

RESULTS

There was no trend towards a lower risk of spontaneous preterm delivery, neither at <37 weeks of nifedipine vs. placebo (11.4% vs. 19.0%; p = 0.320), or <32 weeks (2.3% vs. 2.4%; p = 0.973). Nifedipine reduced spontaneous preterm delivery <37 weeks (p = 0.015) in the multiparous women by stratified analysis for parity. SECONDARY OUTCOMES between the groups did not differ except for a higher percentage of maternal side-effects in the nifedipine group (31.8%) vs. placebo (11.9%) (p < 0.05). Subgroup analysis showed a borderline (p = 0.047) lower percentage of spontaneous preterm delivery in women with a ultrasonographic cervical length of <20 mm in the nifedipine group.

CONCLUSIONS

Prophylactic nifedipine in asymptomatic women at high risk for preterm delivery had a positive effect on the rate of spontaneous preterm delivery <37 weeks in multiparous women.

Emergency cerclage: literature review

This article reviews the use and effectiveness of emergency cerclage for women who present with a dilated cervix in the second trimester of pregnancy and seeks to identify predictors of favorable emergency cerclage outcomes. We searched PubMed and the Cochrane Library for the period January 1995 to April 2012 and used the terms "emergency cerclage," "emergency stitch," "rescue cerclage," and "rescue stitch." Thirty-four studies in which transvaginal emergency cervical cerclage was performed in women with a dilated cervix were identified and included. Predictors of poor outcome were prolapsed membranes, evidence of intra-amniotic or systemic infection, symptomatic presentation, cervical dilatation greater than 3 cm, or cerclage after 22 weeks. According to observational and limited randomized controlled trials, the cerclage group did significantly better than the bed-rest group in mean randomization-to-delivery interval, preterm delivery before 34 weeks, and compound neonatal morbidity. The current data suggest that emergency cerclage is associated with a longer latency period and, most often, with better pregnancy outcomes when compared with bed rest. Many of the predictors of adverse outcomes appear to be associated with evidence of inflammation or infection.

TARGET AUDIENCE

Obstetricians and gynecologists, family physicians

LEARNING OBJECTIVES

After completing this CME activity, physicians should be better able to review the use and evaluate the effectiveness of emergency cerclage for women who present with a dilated cervix in the second trimester, to identify predictors of favorable emergency cerclage outcomes, and to compare emergency cerclage versus bed rest.

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.

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.

Predictive model for spontaneous preterm labor among pregnant women with contractions and intact amniotic membranes

PURPOSE

To determine a predictive model for supporting decisions relating to the prognosis for women presenting with preterm labor and intact membranes.

METHOD

We conducted a prospective observational cohort study on 70 pregnant women at between 22 and 34 weeks of gestation. Transvaginal sonographic evaluation on the cervix was performed once on women who had completed a course of parenteral tocolysis. The sonographic parameters of cervical length measurement and presence of cervical glandular area were obtained. The outcome variable was occurrences of preterm delivery (<35 weeks). Using a univariate logistic regression model, the coefficients of each independent variable were first estimated. To construct the predictive model, multivariate logistic regression containing all the selected variables that might be related to preterm delivery was used as the starting point. Accuracy, sensitivity, specificity and predictive values were used to measure associations of predicted probabilities and to check the ability of the model to predict outcomes. The predictive analyses were based on logistic regression models, with calculation of odds ratios and 95 % confidence intervals.

RESULTS

The incidence of preterm delivery was 32.80 % (23/70). After validation, the predictive model proposed showed accuracy of 87.88 %, sensitivity of 78.26 % and specificity of 93.02 %.

CONCLUSION

The model presented good accuracy with correspondence between predictions and observations, and has the capacity to become a useful tool for management of pregnant women with preterm labor and intact amniotic membranes.

Usefulness of cervical volume by three-dimensional ultrasound in identifying the risk for preterm birth

This study was conducted to establish the relationship between three-dimensional (3-D) cervical volume and the risk of spontaneous preterm birth. A total of 391 asymptomatic women with singleton pregnancies were prospectively evaluated two-dimensional cervical length and 3-D cervical volume at 20-24 weeks of gestation. We assessed the relationship between cervical factors and the risk for preterm birth before 36 weeks of gestation. Logistic regression analysis demonstrated that not only cervical length (odds ratio [OR], 0.94; 95% confidence interval [CI], 0.88-0.99, p = 0.002), but also cervical volume (OR, 0.26; 95% CI, 0.11-0.61, p = 0.045) was independent predictor of preterm birth. A combined approach in which a gravida was regarded as positive with a short cervical length (≤28 mm) or a small cervical volume (≤20 cm(3)) had a sensitivity of 57.1% for preterm birth. Screening combining cervical length and volume may provide a better prediction of preterm birth.

Avaliação do comprimento do colo uterino em gestantes normais entre 20 e 34 semanas de gestação por meio da ultrassonografia endovaginal

OBJETIVO: Avaliar o comprimento do colo uterino pela ultrassonografia transvaginal em uma população de gestantes normais e construir uma curva de normalidade no período de 20 a 34 semanas de gestação. MATERIAIS E MÉTODOS: Estudo de corte transversal, incluindo 145 gestantes normais, com feto único, vivo, sem enfermidades, entre 20 e 34 semanas de gravidez, examinadas nos serviços de ultrassonografia do Hospital Universitário Júlio Müller e de uma clínica privada. As gestantes foram submetidas a ultrassonografia endovaginal, com registro do comprimento cervical. Critérios de exclusão foram: parto prematuro, rotura prematura pré-termo das membranas, placenta prévia, uso de fármacos tocolíticos e/ou progesterona, cerclagem ou qualquer intervenção cirúrgica prévia no colo. A associação entre o comprimento do colo uterino e a idade gestacional foi examinada por regressão linear. RESULTADOS: O comprimento cervical diminuiu progressivamente em 0,8 mm a cada semana, à medida que a idade gestacional progrediu (r = -0,351; p < 0,001). As mulheres que tiveram afunilamento cervical apresentaram colo mais curto que as demais (p = 0,001). A interpolação dos percentis 5, 50 e 95 provê gráfico passível de ser utilizado como referência. CONCLUSÃO: O comprimento médio cervical em gestantes normais diminui 0,8 mm por semana, entre a 20ª e a 34ª semanas de gestação.

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.

Ultrasonographic assessment of cervix size and its correlation with female characteristics, pregnancy, BMI, and other anthropometric features

PURPOSE

Cervical length during the first trimester of pregnancy has not been completely investigated yet. The objective of our study is to compare cervical size in the first ten gestational weeks with that of non-pregnant women, and to determine its correlation with maternal factors, including age, anthropometric features, and reproductive history.

METHODS

We collected retrospective data about women who applied to the Obstetrics and Gynecology Outpatients Facility of Udine between February and June 2009, selecting both pregnant and non-pregnant women possessing a transvaginal ultrasonographic measurement of their cervix, and focusing on their age, parity, BMI, cervical, and uterine size. Data were analyzed by R (version.2.8.0), considering significant P < 0.05.

RESULTS

135 women were recruited. By multivariate linear regression, both cervical length and width result independently influenced by pregnancy status, and among non-pregnant nullipara, cervical length results to be significantly lower in women younger than 20 (P < 0.05).

CONCLUSIONS

During the first ten gestational weeks, cervix results to be longer and wider than in non-pregnant women, suggesting the possible existence of early gestational, morphological, uterine, and cervical modifications. Women under the age of 20 have a significantly shorter cervix, suggesting an incomplete cervix maturity in this group of women, which may justify the higher prevalence of pre-term births in teenage pregnancies.

Methods of sonographic cervical length measurement in pregnancy: A review of the literature

In this review we give an overview of the methods and pitfalls in cervical length measurements. We compared the different techniques and investigated factors that influence visualization of the cervix. The data in this overview may be used to establish guidelines in clinical practice.

Dynamic cervical length changes: Preliminary observations from 30-minute transvaginal ultrasound recordings

OBJECTIVE

The purpose of this study was to visualize and quantify dynamic changes in the cervix and to study factors influencing cervical length.

METHODS

Eighteen women with a gestational age between 23 and 40 weeks were examined by transvaginal ultrasound during a continuous observation period of 30 minutes.

RESULTS

All women delivered at >34 weeks of gestation, fourteen at term. The overall mean difference between the shortest and longest cervical length during the 30-minute recordings (cervical length variation) was 10.9 mm (range 1.6-26.7 mm). In the presence of fetal movements directed at the cervix, peristaltic movement of the bowel or contractions, cervical length variation was larger than in the absence of these conditions (mean 12.7 mm, range 5.2-26.7 mm and mean 6.1 mm, range 1.6-9.4 mm, respectively; p = 0.03).

CONCLUSIONS

Dynamic changes in cervical length are present at early gestation and long before delivery and can be observed either spontaneously or associated with contractions, fetal movements or peristalsis. These conditions must be considered as pitfalls in cervical length measurement. In critical cases, such as early threatened preterm labor, increases in the frequency and duration of sonographic ultrasound measurements may be helpful to obtain a more reliable estimation of the cervical status.

Cervical length and risk of antepartum bleeding in women with complete placenta previa

OBJECTIVE

To evaluate if cervical length predicts prepartum bleeding and emergency Cesarean section in cases of placenta previa.

METHODS

Between September 2005 and September 2007, cervical length was measured by transvaginal ultrasound in women with complete placenta previa persisting into the third trimester of pregnancy. A complete follow-up of pregnancy was obtained in all cases.

RESULTS

Overall, 59 women were included in the study group. The mean +/- SD gestational age at ultrasound was 30.7 +/- 2.7 weeks and the cervical length was 36.9 +/- 8.8 mm. Cesarean delivery was performed in all cases, at a mean gestational age of 34.7 +/- 2.3 weeks. Twenty-nine (49.1%) of the women presented prepartum bleeding and 12 (20.3%) required an emergency Cesarean section prior to 34 completed weeks due to massive hemorrhage. Cervical length did not differ significantly between cases with and those without prepartum bleeding (35.3 +/- 9.3 mm vs. 38.4 +/- 8.2 mm; P = 0.18), but was significantly shorter among patients who underwent emergency Cesarean section < 34 weeks due to massive hemorrhage compared with patients who underwent elective Cesarean section (29.4 +/- 5.7 mm vs. 38.8 +/- 8.5 mm; P = 0.0006).

CONCLUSIONS

Transvaginal sonographic cervical length predicts the risk of emergency Cesarean section < 34 weeks in women with complete placenta previa.

Sonographic longitudinal cervical length measurements in nulliparous women at term: prediction of spontaneous onset of labor

OBJECTIVE

The aim of this study was to predict spontaneous onset of labor by serial transvaginal ultrasound measurement of cervical length (CL) in a homogeneous population of nulliparous women at term.

METHODS

162 nulliparous women with singleton fetuses in cephalic presentation were examined at weekly intervals from 36 weeks' gestation to delivery. CL was measured by transvaginal ultrasound in the supine and upright positions.

RESULTS

There was a significant decrease in CL in the last 12 days prior to delivery. However, this decrease was small with substantial variation between individuals. Women with spontaneous onset of labor could be divided into three different groups: those with unchanged CL before delivery; those with a fall in CL in the last 2 weeks prior to delivery; and those with a gradual change in CL starting before the last 2 weeks prior to delivery. A single CL measurement below 30 mm between 37 and 38 weeks of gestation predicted spontaneous onset of labor before 41 weeks' gestation with a sensitivity of 46%, specificity of 78%, positive predictive value (PPV) of 82%, negative predictive value (NPV) of 40% in the supine position; and sensitivity of 53%, specificity of 72%, PPV of 81%, NPV of 40% in the upright position.

CONCLUSION

Between 37 and 38 weeks' gestation, spontaneous onset of labor before 41 weeks can be predicted by a CL measurement, but with low sensitivity and NPV. Inter-individual variations in CL and in CL changes are large, which hampers the value of single and repeated CL measurements for the prediction of spontaneous onset of labor at term.

Avaliação biométrica do colo uterino durante a gestação por meio da ultra-sonografia transvaginal e ressonância magnética

OBJETIVO: Avaliar o comprimento do colo uterino por meio da ressonância magnética e comparar aos achados da ultra-sonografia transvaginal. MATERIAIS E MÉTODOS: Foram realizados exames ultra-sonográficos e de ressonância magnética do colo uterino em 20 pacientes com idade gestacional entre 19 e 30 semanas. As medidas do colo obtidas pelo exame de ressonância magnética foram aferidas por dois especialistas em diagnóstico por imagem, para calcular a variabilidade interobservador do método. RESULTADOS: O cálculo do coeficiente de correlação de Pearson entre as medidas do comprimento cervical indicou correlação significante entre os métodos (r=0,628; p<0,01). A aplicação do teste t pareado não evidenciou diferença significativa entre as medidas aferidas pela ultra-sonografia transvaginal e ressonância magnética (p=0,068). A análise da variabilidade interobservador das medidas do colo obtidas pela ressonância magnética demonstrou alta confiabilidade do método (a=0,96). CONCLUSÃO: A comparação entre os dois métodos de imagem na avaliação da biometria cervical não apresentou diferença estatística, o que reforça a aplicação do exame ultra-sonográfico. Entretanto, em situações nas quais a ultra-sonografia transvaginal apresenta contra-indicações, o exame de ressonância magnética poderá apresentar-se como segunda opção para a avaliação do comprimento cervical.

Progressive cervical length changes versus single cervical length measurement by transvaginal ultrasound for prediction of preterm delivery

BACKGROUND

To evaluate cervical length changes as predictors of preterm delivery.

METHODS

Two hundred and fifty-seven pregnant women underwent transvaginal ultrasound examination at 16 and 24 weeks of gestation. Cervical length was measured and the difference between the 2 measurements was calculated. The sensitivity, specificity, positive predictive value and negative predictive value of cervical length and cervical length changes were calculated and these methods were compared by receiver-operating characteristic (ROC) curve analysis.

RESULTS

Preterm delivery (before 37 weeks of gestation) occurred in 19 patients (7.4%). The mean cervical length was shorter in the preterm group, the area under the ROC curve for prediction of preterm delivery was 0.914, ultrasound had a sensitivity of 84.2% to predict preterm delivery with a false-positive rate of 18.5%, and the relative risk was 4.56 at the 34.3-mm cutoff value at 24 weeks of gestation. In contrast, a cervical length change on transvaginal ultrasound had a sensitivity of 73.3% to predict preterm delivery with a false-positive rate of 18.1%, and the relative risk was 4.08 at the 6.6-mm cutoff value.

CONCLUSION

A single cervical length measurement obtained at 24 weeks of gestation can predict preterm delivery as accurately as cervical length change.

Intra-amniotic sludge, short cervix, and risk of preterm delivery

OBJECTIVE

To evaluate the association between intra-amniotic sludge seen at cervical ultrasound and preterm delivery.

METHOD

This retrospective study included women at high risk for preterm delivery who were referred for second trimester cervical length measurement by ultrasound between 18 and 32 weeks' gestation. Patients with multiple gestations, cerclage, or preterm labour were excluded. Ultrasound images were reviewed by two independent observers and divided into three groups: (1) no amniotic sludge, (2) light sludge, and (3) dense sludge in the amniotic fluid. The primary outcome measures were delivery within 14 days of examination and delivery before 34 weeks' gestation. Logistic regression analyses were performed to adjust for confounding factors.

RESULTS

Eighty-nine patients met the inclusion criteria. Mean gestational age at presentation was 25.8 +/- 4.4 weeks, and mean cervical length was 33 +/- 12 mm. The prevalence of light and dense amniotic fluid sludge was 10.1% and 5.6%, respectively. Delivery within 14 days of examination occurred in four (5.3%) women with no sludge, in two (22.2%) women with light sludge, and in three (60.0%) women with dense sludge (P < 0.01). Delivery before 34 weeks occurred in five (6.7%), four (44.4%) and four (80.0%) women, respectively (P < 0.01). Logistic regression analyses demonstrated that light amniotic fluid sludge, dense sludge, and cervical length of less than 25 mm were all significant and independent predictors of delivery within 14 days of examination and delivery prior to 34 weeks.

CONCLUSION

The presence of amniotic fluid sludge is associated with delivery within 14 days and delivery before 34 weeks' gestation.

Cervical gland area as an ultrasonographic marker for preterm delivery

OBJECTIVE

To assess the association between spontaneous preterm delivery (SPTD) in the general population and the measurement of the cervix length, cervical funneling, and absence of the cervical gland area (CGA).

METHOD

A prospective cohort of 338 women carrying uncomplicated pregnancies was evaluated by transvaginal sonography between 21 and 24 weeks' gestation.

RESULTS

Measurement of cervical length with less than 20 mm and the presence of cervical funneling presented a statistically significant association with SPTD before 35 weeks. The non-detection of CGA demonstrated a strong association with SPTD before 37 weeks' (p < 0.001; OR = 194.5) and before 35 weeks' gestation (p < 0.001; OR = 129.6). The multiple logistic regression analysis suggested the non-detection of CGA as the only variable to reveal statistically significance association with SPTD.

CONCLUSION

The results seem to indicate that the absence of CGA can be a new and important ultrasound marker for SPTD, to be confirmed by future multicenter investigations.

Evaluation of effectiveness of prophylactic cerclage of a short cervix according to interleukin-8 in cervical mucus

OBJECTIVE

This study was undertaken to compare rates of preterm delivery according to cervical mucus interleukin-8 (IL-8) among women who underwent cerclage because of a short cervix.

STUDY DESIGN

This retrospective study included 16,508 patients whose cervical length and cervical mucus IL-8 concentrations were measured between 20 and 24 weeks. A short cervix was defined by a length of 25 mm or less, whereas IL-8 concentrations exceeding 360 ng/mL were considered high. Whether to perform cerclage was decided by clinicians without consideration of IL-8 concentrations.

RESULTS

Among all subjects, a significantly smaller percentage of subjects avoided delivery before 37 weeks when cervical mucus IL-8 was elevated (P = .0302) or the cervix was short (P < .0001). Among patients with a short cervix, preterm delivery was more likely when cervical mucus IL-8 was elevated. Overall, risk of preterm delivery in patients with a short cervix did not differ between those undergoing and not undergoing cerclage. However, among patients with a short cervix, those with normal IL-8 concentrations in cervical mucus were less likely to have preterm delivery if they underwent cerclage (before 37 weeks, 33% vs 54.5%, P = .01; before 34 weeks, 4% vs 13.6%, P = .03). In contrast, when cervical mucus IL-8 was high, delivery before 37 weeks was more likely with than without cerclage (78% vs 54.1%, P = .03).

CONCLUSION

With normal cervical mucus IL-8, cerclage treatment for cervical shortening may reduce the rate of preterm delivery, but with elevated cervical mucus IL-8 cerclage may be harmful.

[Significance and limitations of obstetrical ultrasound]

Obstetrical ultrasound is practised in Germany, Austria and Switzerland as a screening examination for all pregnancies. Although the reasons for its introduction in Germany in 1981 were dating of pregnancy, detection for multiple pregnancies and detection of intrauterine growth retardation, its aims has shifted towards the detection of fetal malformations when the 3-point obstetrical screening was introduced in 1995. To produce a realistic quality for this large number of examiners, a multi-level system was introduced. Today, contents and quality requirements of the 3 screening examinations (at 10/20/30 weeks), the 3 levels of examination and of the ultrasound equipment can be defined. This should help optimize the still insufficient quality of obstetrical ultrasound and reduce unrealistic expectations.

Prediction of Preterm Delivery in the Second Trimester

OBJECTIVE

The aim of this study was to estimate the probability of spontaneous delivery at 34 weeks or less according to cervical assessment by transvaginal scan associated with previous obstetric history.

METHODS

Ultrasound transvaginal cervical length and presence of funneling were evaluated in 1,958 singleton pregnancies between 21 and 24 weeks of gestation. For the prediction of preterm delivery, the results of cervical assessment were analyzed in association with the previous obstetric history of preterm delivery, spontaneous miscarriage, and curettage. Sensitivity, specificity, and positive and negative predictive values for the various cutoff cervical lengths in the groups with or without previous history of preterm delivery were calculated. Multivariable regression analysis was used to identify the predictive factors for preterm delivery at 34 weeks or less.

RESULTS

The incidence of spontaneous delivery at gestational age of 34 weeks or less was 3.4%. The mean cervical length was 30.1 mm (standard deviation 10.1 mm) in the group with previous history of prematurity (n = 180) and 35.8 mm (standard deviation 7.9 mm) in the group without previous history of prematurity (P < .001). The mean cervical length in the group of patients who delivered at or before 34 weeks was 23.8 mm, and for patients who delivered after 34 weeks it was 35.6 mm (P < .001). The mean gestational age at delivery was significantly lower in the group with funneling compared with the group without funneling (33.5 weeks versus 38.8 weeks, P < .001). Logistic regression analysis demonstrated that cervical length, funneling, and history of previous preterm delivery were independent contributors for preterm delivery.

CONCLUSION

Ultrasound cervical assessment may be useful in the prediction of preterm delivery, but it should also be considered in association with the obstetric history of prematurity.

Estudo comparativo entre marcadores ultra-sonográficos morfológicos preditores de parto pré-termo: sinal do afunilamento do colo e ausência do eco glandular endocervical

OBJETIVO: Avaliar o risco de parto pré-termo (PPT) espontâneo na população geral a partir do estudo comparativo dos marcadores ultra-sonográficos morfológicos do colo uterino, como o sinal do afunilamento e a ausência da área glandular endocervical. MATERIAIS E MÉTODOS: Foram arroladas 361 gestantes na população geral, submetidas a exame ultra-sonográfico transvaginal entre a 21ª e 24ª semana, e verificados os resultados perinatais. RESULTADOS: A incidência de PPT espontâneo foi de 5,0%. O sinal do afunilamento foi observado em 4,2% da população estudada e em 22,2% das pacientes que evoluíram para PPT espontâneo. Tal parâmetro mostrou associação significante com PPT (p < 0,001; risco relativo de 6,68). A ausência do eco glandular endocervical (EGE) foi detectada em 2,8% das pacientes estudadas e em 44,4% das pacientes que evoluíram para PPT espontâneo. Este parâmetro demonstrou forte associação com PPT espontâneo (p < 0,001; risco relativo de 28,57). A análise de regressão logística multivariada apontou a ausência do EGE como a única variável morfológica associada ao PPT espontâneo. CONCLUSÃO: A predição do PPT espontâneo a partir de sinais ultra-sonográficos deve ser realizada contemplando marcadores biométricos e morfológicos, entre estes, a ausência do EGE. Este estudo indica uma tendência clara da marcante importância da ausência do EGE como indicador do risco para PPT espontâneo, a ser confirmada futuramente em pesquisas multicêntricas.

Controversies regarding cervical incompetence, short cervix, and the need for cerclage

Cervical incompetence (CI) is not an all or nothing phenomenon but a continuous variable. CI and preterm labor are not distinct entities but rather part of a spectrum leading to preterm delivery. Cervical length (CL) is an independent variable in the prediction of preterm delivery, to which it is inversely related. Application of a primary transvaginal cervical cerclage appears to be an unnecessary intervention in about 50% of women presenting with a history suggesting cervical incompetence. A better alternative for women with a history of or risk factors for CI is transvaginal ultrasonographic follow-up of CL. To facilitate the comparison of studies of CI, the authors suggest a nomenclature reflecting the different stages of prevention: primary, secondary, and tertiary transvaginal cervical cerclage.

Role of ultrasound in screening patients at risk for preterm delivery

The ultrasound assessment of the cervix has contributed to the understanding of the pathways to preterm birth. Transvaginal ultrasound measurement of the cervix provides an objective and noninvasive tool for the evaluation of cervical status. Despite widespread use of this procedure, standardization of measurement indications, technique, and interval between examinations has not been achieved. The American College of Radiology has recently recommended that the cervix and lower uterine segment be imaged as part of every obstetric ultra-sound examination in the second trimester. These guidelines specifically suggest a search for a short cervix (less than 30 mm) or funneling. The expert panel on women's imaging further recommended evaluating the cervix sonographically on both the initial examination and all follow-up examinations for twin gestations. The American Institute of Ultrasound in Medicine guidelines indicate that evaluation of the uterus, including cervix, should be performed, but does not indicate specifically that the cervix should be measured. In contrast, the American College of Obstetricians and Gynecologists, although recognizing that cervical length assessment may be helpful in predicting the risk of preterm delivery (particularly from a negative predictive value), does not recommend routine use of cervical length measurement because of the lack of proved treatment or intervention methods. A review of the literature suggests that at the time of this writing the role of routine screening of low-risk women with cervical length assessment by ultrasound is not supported. In contrast, in women at risk for preterm delivery(eg, women with a prior history of preterm birth or women with multiple gestations) cervical length assessment may be useful for its negative predictive value. At present, however, there is no therapeutic intervention that has been proved to decrease the risk of preterm delivery in women with a documented cervix on ultrasound.

Menace d’accouchement prématuré sévère précoce : est-il licite de ne pas transférer in utero et comment gérer une naissance en centre de niveau I et II ?

The frequency of premature delivery is estimated at 0.5% of births (approximately 2000 per year in France). The rate of in utero transfers before 28 weeks, although difficult to evaluate, is well above this percentage, raising the risk of overloading level III maternity wards. Who should or should not be transferred? What tests are most pertinent? What are the criteria for diagnosing premature labor? Which treatment should be offered? How should the decision to transfer be established? What information should be furnished to the parents? How should an unexpected delivery be managed? How should the transfer network be optimally organized?

Effectiveness of cervical cerclage for a sonographically shortened cervix: a systematic review and meta-analysis

OBJECTIVE

The purpose of this study was to determine the effectiveness of cerclage for a shortened cervix on transvaginal ultrasound scanning in terms of the rates of preterm delivery and adverse neonatal and maternal outcomes.

STUDY DESIGN

Pre-MEDLINE and MEDLINE, EMBASE, and the Cochrane Library were searched for human studies that compared cerclage placement to no cerclage on the basis of transvaginal ultrasound findings of a short cervix (< or =2.5 cm). Two authors independently determined eligibility and abstracted data. Meta-analyses were conducted when possible.

RESULTS

Thirty-five studies were reviewed; 6 studies were eligible and were included in the analysis. There was no statistically significant effect of cerclage on the rates of preterm delivery (<37, <34, <32, and <28 weeks of gestation), preterm labor, neonatal mortality or morbidity, gestational age at delivery, or time to delivery. Birth weight was significantly higher with than without cerclage (P=.004).

CONCLUSION

The available evidence does not support cerclage for a sonographically detected short cervix. A randomized controlled trial is needed to determine whether this intervention will reduce adverse neonatal outcomes.

Sonographic assessment of the cervix before, during and after a uterine contraction is effective in predicting the course of labor

OBJECTIVE

To investigate whether the degree of change in cervical length during a uterine contraction is predictive of subsequent progression of labor.

METHODS

The subjects were 73 uncomplicated parturient women at term. We observed the cervix before, during and after a uterine contraction by transvaginal ultrasound in the first stage of labor and determined the degree of cervical shortening during the contraction relative to the cervical length before contraction. We related the degree of cervical shortening to labor patterns at the time of the ultrasound examination, which were retrospectively determined by reviewing the partogram.

RESULTS

The cervix was shortened in length by about 50% on average during a uterine contraction in the normal course of labor. The degree of cervical shortening was significantly greater in the normal latent and active phases than it was in the prolonged latent phase, protracted active phase and false labor, whereas there were no differences between the former two phases nor between the latter three phases. Nulliparous and parous women exhibited almost the same degree of shortening in the normal latent and active phases.

CONCLUSIONS

Real-time ultrasound observation of the cervix during uterine contraction could help differentiate inefficient uterine contractions from normal ones and thus predict the subsequent course of labor.

Expression and regulation of the rat prostaglandin E2 receptor type 4 (EP4) in pregnant cervical tissue

OBJECTIVE

Prostaglandins play an important role in the regulation of parturition and cervical ripening. Prostaglandin E(2) (PGE(2))-induced tissue remodeling is mediated through activation of prostaglandin E(2) receptor type 4 (EP4). EP4 is known to regulate matrix metalloproteinase secretion and expression and therefore may play a role in cervical ripening. We hypothesized that EP4 expression is regulated in the rat cervix to coincide with cervical ripening. In addition, we analyzed transcriptional regulation of the rat EP4 gene.

STUDY DESIGN

EP4 expression was evaluated in the cervix in timed pregnancy Sprague-Dawley rats by real-time reverse transcriptase polymerase chain reaction and Western blot. The genomic structure of the rat EP4 gene was determined by sequencing rat genomic clones obtained by plaque hybridization. Northern blots were performed to identify the number of different transcripts. The transcriptional start site was identified on the basis of sequence comparison to the human and mouse EP4 gene. The minimal promoter was identified by using reporter constructs containing portions of the 5' flanking region. Reporter activity was evaluated in vitro. Identified regulatory regions were mutated to determine their role in transcription.

RESULTS

Cervical EP4 expression (messenger RNA and protein) peaks on the day of parturition. The rat EP4 gene is structurally similar to other prostaglandin receptors as well as the human EP4 gene and contains three exons separated by two introns. The coding regions are located in the second and third exons separated in the sixth transmembrane spanning region. Northern blot identified a single EP4 transcript with an estimated size of 4 kb, indicating a single transcription initiation site. The first 80 bases of the 5' flanking region were required for constitutive expression of EP4. Expression was lost after mutation of the GC/Sp1 binding site located at position -78 to -66 downstream from the transcription initiation site. Three Sp1 binding sites were identified and appear to cooperate to enhance EP4 transcription.

CONCLUSION

EP4 expression is regulated in the cervix and peaks on the day of parturition. The genomic structure of the human and rat EP4 gene is conserved between these two species. A GC rich/Sp1 binding site located within the first 80 bases of the transcription start site is important in transcription initiation of the EP4 gene.