Transvaginal and transabdominal ultrasonography of the uterine cervix during pregnancy.

Transvaginal and transabdominal ultrasound evaluation of the uterine cervix were compared in a study of 186 pregnant women. An empty bladder made transabdominal ultrasound measurement of the cervix more difficult, while bladder filling resulted in significant lengthening of the transabdominal cervical measurement. In contrast, transvaginal ultrasound cervical measurement was possible in all but 1 patient. Normal transvaginal ultrasound cervical measurements were significantly shorter on average than transabdominal cervical measurements, but compared closely with prior transabdominal ultrasound studies in which bladder filling was carefully controlled. Significant cervical shortening was not noted in most patients with a clinical diagnosis of incompetent cervix.     

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

Different strategies have been developed to refine the prediction of the risk of preterm delivery in asymptomatic patients. Transvaginal sonography has been used for this reason to measure and examine the length and shape of the cervix. In this review, we focus on clinical studies involving transvaginal sonographic assessment of the cervix in asymptomatic women at high risk of preterm delivery and in the general pregnant population. Three ultrasound signs are suggestive of cervical incompetence, namely, dilatation of the internal os, sacculation or prolapse of the membranes into the cervix (with shortening of the functional cervical length) either spontaneously or induced by transfundal pressure, and short cervix in the absence of uterine contractions. Transvaginal sonography has clearly demonstrated that cerclage leads to a measurable increase in cervical length which may contribute to the success of this procedure in reducing the risk of preterm delivery. Several non-randomized interventional studies among patients with cervical incompetence have been published. They have defined a new group of patients requiring cerclage when the women show progressive cervical modifications on transvaginal sonography, while in other studies, cerclage performed on the basis of cervical changes on transvaginal sonography did not prevent premature delivery. One prospective randomized trial in asymptomatic high-risk women has shown two benefits of cerclage following indications for transvaginal sonography: (1) it would generate fewer prophylactic cerclages in high-risk women; (2) therapeutic cerclage before 27 weeks may reduce the incidence of premature delivery before 34 weeks. The risk of preterm delivery is inversely correlated with cervical length. Routine transvaginal sonography of the cervix performed between 18 and 22 weeks can help identify patients at risk of preterm delivery. However, given the low prevalence of preterm births, screening would generate either a high false-positive rate or a low sensitivity. One non-randomized interventional study among patients with a short cervix on routine ultrasound examination found a lower risk of delivery before 32 weeks in the cerclage group than in the expectant management group. However, to date, there have been no prospective randomized trials in a general population. Although evidence is still lacking, there does appear to be a benefit in performing a cerclage rather than continuing with expectant management in cases with sonographic appearance of cervical incompetence in asymptomatic women at high risk of preterm delivery. Ultrasound can be offered to reduce the indications of cerclage for cases in which the situation is uncertain. Within the general obstetric population, transvaginal sonography might help in the selection of asymptomatic but high-risk women. However, the benefit associated with cerclage for sonographic indication has not been demonstrated.     

超声检测宫颈长度预测早产的临床价值

目的探讨超声检测宫颈长度（cervicallength,CL）对先兆早产孕妇发生早产的预测价值。方法对2147例单胎先兆早产初产孕妇,分别经腹部、经阴道、经会阴超声检测CL,以CL〈2．6cm为宫颈缩短,追踪妊娠结局,比较三种方法对早产的预测价值。结果经腹部超声检测747例,CL〈2．6cm者早产率40．93％,CL≥2．6cm者早产率4．51％;经阴道超声检测689例,CL〈2．6cm者早产率69．85％,CL≥2．6cm者早产率1．45％;经会阴超声检测711例,CL〈2．6cm者早产率61．54％;CL≥2．6cm者早产率1．98％,三种检测方法检测的CL〈2．6cm组与CL≥2．6cm组的早产率差异均有统计学意义（P〈0．05）;经腹部、经阴道、经会阴超声测量预测早产的敏感性分别为78．57％、92．23％、89．72％,特异性分别为80．00％、93．00％、90．07％,阳性预测值分别为40．93％、69．85％、61．54％,阴性预测值分别为95．49％、98．55％、98．02％,经会阴、经阴道超声测量预测早产的敏感性、特异性、阳性预测值、阴性预测值均显著高于经腹部（P〈0．05）。结论超声检测CL对先兆早产孕妇发生早产有一定的预测意义。经会阴、经阴道超声预测早产的准确性优于经腹部超声。经会阴超声检测可以替代经阴道超声检测,从而提高患者治疗依从性。     

经阴道超声监测孕妇宫颈形态预测早产的价值

目的评价经阴道超声监测宫颈形态变化对早产的预测价值。方法 223例孕妇分为足月分娩组134例和先兆早产组89例,分别于孕24、28、32及36周行经阴道超声检查,观察宫颈形态长度的变化,以及宫颈指数,并对其妊娠结局进行随访。结果足月分娩组中宫颈长度随孕周增大而缩短;先兆早产组孕妇的宫颈长度均较相应孕周的足月分娩组短,其中24、28及36周组间比较,差异有统计学意义(P<0.05)。先兆早产组各孕周的宫颈指数均较足月分娩组大,两组比较差异有统计学意义(P<0.05)。89例先兆早产组中71例保胎成功,18例发生早产。先兆早产组中21例有宫颈漏斗形成,18例早产者均有宫颈漏斗形成。漏斗形成预测早产的敏感性为100%、特异性为96.6%;以足月分娩孕妇28周时的宫颈长度2.61cm为临界值,其预测早产的敏感性为83.3%、特异性为100%。结论经阴道超声实时监测宫颈形态结构变化对预测早产的发生有一定的临床价值。     

Transvaginal sonography of cervical width and length during pregnancy.

Transvaginal ultrasonography has been proposed as a reliable method of assessing dimensions of the cervix. The purpose of the current investigation was to establish normative data for cervical width and length during pregnancy. This information may be helpful in predicting patients at risk for preterm birth. A transvaginal 5 or 7.5 MHz transducer was used on 132 consecutive low-risk pregnant women undergoing evaluation for gestational dating purposes. Even in cases of patient obesity or an empty bladder, high resolution was possible and permitted cervical measurement in all but one case. The external cervical width at the vaginal fornices was found to increase with advancing gestation (R = 0.512, P < 0.005). The cervical length from internal os to external os was found not to change with advancing gestation (R = 0.11, P = 0.30). Using these normative data, investigation is recommended to determine whether measuring cervical width and length is useful in predicting preterm labor and delivery.     

Cervical changes in twin pregnancies observed by transvaginal ultrasound during the latter half of pregnancy: a longitudinal, observational study.

OBJECTIVE: To determine what constitutes normal cervical changes in twin gestations during the latter half of pregnancy, and whether there are differences in the pattern of cervical change between women expecting twins giving birth at term (> or = 36 completed gestational weeks, GW) and preterm. METHODS: Twenty women (12 nulliparous, eight parous) expecting twins were examined with transvaginal ultrasound every week from 24 GW until delivery. Cervical length and width were measured, the inner cervical os was assessed as being closed or open, and any dynamic cervical changes were noted. Examination results were unavailable to the staff involved in the care of the women. RESULTS: Eight women (40%) delivered preterm spontaneously at 32-35 GW. Cervical length remained unchanged ( approximately 10 mm) in one woman, who delivered preterm. It decreased in the remaining 19 women. The median shortening rate for women manifesting a continuous shortening of the cervix was 2.9 (0.8-5.2) mm/week in women giving birth preterm vs. 1.8 (0.8-2.4) mm/week in those who gave birth at term (P = 0.08). Median cervical length at the first examination was similar in women who delivered preterm and at term (39 vs. 41 mm), but at 32 GW the cervix was shorter in women who delivered preterm (median, 18 vs. 31 mm, P = 0.02). Cervical width remained unchanged in 63% (5/8) of the women who delivered preterm vs. 8% (1/12) of those who gave birth at term (P = 0.02). The cervix became wider in the remaining women. Median cervical width at the first examination was similar in women who delivered preterm and at term (38 vs. 38 mm), but in women who delivered preterm the cervix was thinner at 0-6 days before spontaneous start of labor (median, 40 vs. 48 mm, P = 0.07). An opening of the inner cervical os was seen < or = 27 GW in 88% (7/8) of the women who delivered preterm vs. 17% (2/12) of those who delivered at term (P = 0.006), the corresponding figures for dynamic changes being 63% (5/8) vs. 17% (2/12) (P = 0.06). Dynamic changes were seen in a greater proportion of the examinations in women who delivered preterm (median, 25% vs. 4%, P = 0.07). CONCLUSIONS: The pattern of cervical changes from 24 GW to delivery differs between twin pregnancies delivering preterm (at 32-35 GW) and at term (> or = 36 GW). In twin pregnancies delivered preterm cervical shortening is more rapid, the cervix does not broaden to the same extent as in twins delivered at term, an open inner cervical os and dynamic cervical changes are seen earlier in gestation, and dynamic cervical changes are seen more often. Cervical changes in women with twins who give birth as early as at 24-31 GW may be different.     

The cervix as a predictor of preterm delivery in 'at-risk' women.

OBJECTIVE: To examine the relationship between ultrasound-determined cervical status and pregnancy outcome in women 'at-risk' of spontaneous preterm delivery. DESIGN: A prospective cohort study of 120 pregnant women considered to be 'at-risk' of spontaneous preterm delivery by their clinician. Transvaginal ultrasound of the cervix was used to assess overall cervical length, closed endocervical canal length, diameter and internal os dilatation in the second trimester. The main outcome measure was occurrence of spontaneous preterm birth (< 34 and < 37 weeks of gestation). RESULTS: The overall preterm delivery rate (< 37 weeks gestation) in these women was 35% (n = 42) with 20% (n = 24) delivering < 34 weeks gestation. Of the 71 women with a normal cervix, 8 (11%) delivered < 34 weeks, whereas of the 49 women with an abnormal cervix, 16 (33%) delivered < 34 weeks (RR 2.90; 95% CI 1.35-6.24). Using linear regression, closed endocervical canal length of < 21 mm before 20 weeks is associated with delivery < 34 weeks in 95% of women, and with delivery < 37 weeks in 95% of women if the canal length is < 33 mm. Logistic regression showed closed endocervical canal length to be the only significant factor in those women who delivered < 34 weeks after controlling for possible confounders. CONCLUSIONS: A strong relationship is demonstrated between cervical status and pregnancy outcome, particularly the cervical findings before 20 and 24 weeks of gestation. The length of the closed portion of the endocervical canal is the best predictor. A beneficial effect of this approach to 'at-risk' women is the reduction in unnecessary interventions in those with normal cervical findings.     

Morphology assessed by transvaginal ultrasonography differs in patients in preterm labor with vs. without bacterial vaginosis.

OBJECTIVE: To determine whether cervical morphology in preterm labor patients differs in the presence or absence of bacterial vaginosis. DESIGN: Observational study. SUBJECTS: One hundred and twelve consecutive patients with objectively confirmed preterm labor admitted to a tertiary care centre were included in the study. Patients with placenta previa, active uterine bleeding or indication for an immediate delivery (e.g. severe pre-eclampsia or suspected fetal asphyxia), or severe fetal anomalies were excluded. METHODS: Transvaginal ultrasonography was used to measure cervical length and internal os width. Bacterial vaginosis was diagnosed by Gram stain of a vaginal smear. RESULTS: A total of 36 patients (32%) had bacterial vaginosis. Cervical length in this group was shorter than in patients with normal flora (mean 20.4 +/- 7.2 mm vs. 26.4 +/- 6.7 mm; P = 0.0002), and more patients with bacterial vaginosis had a dilated internal cervical os > or = 5 mm (67% vs. 30%, P = 0.001). There were no significant differences, however, in preterm delivery rate and birth weight between the two groups; the overall preterm delivery rate was 40%. A cervical length < 25 mm was predictive of preterm delivery (P = 0.001, RR 4.2, 95% CI 1.8-9.7). CONCLUSIONS: These data suggest that cervical change in preterm labor is more pronounced in patients with bacterial vaginosis but without a concomitant increase in the risk for preterm delivery. Despite this association, the cervical length measured by transvaginal ultrasonography alone is a useful predictor of preterm delivery, independent of the presence or absence of bacterial vaginosis.     

Evaluation of the upper uterine cervix by the location of the vesicocervical fold of the urinary bladder to rule out cervical shortening during pregnancy with and without premature contractions.

OBJECTIVES: To measure the length of the upper and lower cervix, as demarcated anatomically by the lowermost edge of the urinary bladder, in second- and third-trimester pregnancies with and without premature contractions. We hypothesized that patients with active premature contractions have a shorter upper cervix, placing them at greater risk of preterm delivery. METHODS: The lengths of the total cervix and of the upper and lower cervix, separately, and funnelling of the internal os, were assessed by endovaginal ultrasonography. In 120 women with normal pregnancy (43 of which with premature contractions), cervical dilatation and effacement were determined by digital examination. The correlation of cervical variables with the course of pregnancy was analyzed by the Wilcoxon test. RESULTS: The mean lengths of the upper and lower cervix were 15.9 +/- 1.7 mm (median 16.0 mm) and 26.4 +/- 3.7 mm (median 27.0 mm), respectively, in patients without premature contractions and 6.9 +/- 3.7 mm (median 6.0 mm) and 24.7 +/- 4.7 mm (median 25.0 mm), respectively, in patients with premature contractions. In the latter subgroup, the upper cervix was significantly shorter (p = 0.0001) but the lower cervix remained almost unchanged. Digital palpation was less accurate than transvaginal sonography for evaluating total cervical length. CONCLUSIONS: Transvaginal sonography is the method of choice for assessing cervical changes during pregnancy. In this prospective study, upper cervical length was the best predictor of preterm labor of all cervical parameters studied. Its length could be accurately determined by the location of the lowermost edge of the urinary bladder (vesicocervical fold of the bladder).     

Cervical assessment at the routine 23-weeks' scan: problems with transabdominal sonography.

OBJECTIVES: To compare transabdominal and transvaginal sonographic measurements of cervical length in pregnancy and examine the factors that may influence these measurements. METHODS: The study population consisted of 149 women with singleton pregnancies attending for routine ultrasound examination at 23 weeks of gestation. In all women the cervix was successfully visualized by transvaginal sonography and cervical length was measured after emptying of the bladder. This measurement was compared to that obtained by transabdominal sonography. In addition the ability to visualize the cervix transabdominally was examined in relation to body mass index (BMI), bladder volume and cervical length. RESULTS: The percentage of cases in which the cervix could be seen transabdominally increased from 42% for bladder volume of < 50 ml to 73% for volumes > 150 ml, and 13% for cervical length < 20 mm to 51% for lengths > 40 mm. The ability to visualize the cervix was unrelated to BMI. Although there was a significant association between measurements taken transabdominally with those made transvaginally, measurements taken with a full bladder were significantly longer than those with an empty bladder. CONCLUSION: The aim of cervical assessment in pregnancy is to identify women with a short cervix because they are at high risk of preterm delivery. This aim can not be fulfilled by transabdominal sonography. Such a scan fails to visualize the cervix in a high proportion of cases and in particular those with a short cervix. Furthermore, successful visualization requires a full bladder which falsely increases cervical length.     

Patterns of normal change in cervical length and width during pregnancy in nulliparous women: a prospective, longitudinal ultrasound study.

OBJECTIVES: To determine what constitutes normal changes in the uterine cervix visible at transvaginal ultrasound examination from 24 gestational weeks until delivery in nulliparous women delivering at term. DESIGN: Cervical length and width were measured using transvaginal ultrasound, and the inner cervical os was assessed as being closed or open every 2 weeks from gestational week 24 until delivery in 19 healthy nulliparae delivering at term. RESULTS: In all but one woman cervical length decreased, and in all but one woman cervical width increased, with advancing gestation. Three patterns of change in cervical length were observed: a continuous decrease ( n = 10), an accelerated shortening rate after approximately 30 gestational weeks ( n = 5), or a sudden drop in length between the last two examinations ( n = 3). The median rate of decrease in cervical length was 1 (range, 0.6-1.9) mm/week for women with continuous shortening of the cervix. For women with accelerated shortening the corresponding figure was 2.2 (range, 1.8-2.7) mm/week after the start of accelerated shortening. Two patterns of increase in cervical width (cervical broadening) were noted: a continuous increase ( n = 12), or an accelerated broadening rate from around 32 weeks ( n = 6). The median rate of increase in cervical width was 0.8 (range, 0.3-2.0) mm/week for women with continuous broadening of the cervix. For women with accelerated broadening rate the corresponding figure was 1.7 (range, 1.0-6.4) mm/week after the start of increased broadening rate. Opening of the internal cervical os was observed at least once in eight of the 19 women (42%) and was first observed at 30 gestational weeks. Dynamic changes (i.e. opening and closing of the inner cervical os during examination) were seen in six women (32%) and were first detected at 31 gestational weeks. CONCLUSIONS: There are different patterns of normal change in cervical length and width during pregnancy in nulliparous women. This must be taken into account if repeated ultrasound examinations of the cervix during pregnancy are used to identify nulliparae at increased risk of preterm delivery.     

Cervical incompetence: the use of transvaginal sonography to provide an objective diagnosis.

OBJECTIVE: To investigate the use of transvaginal sonography in monitoring the cervix in women at high risk of a preterm delivery. STUDY DESIGN: One hundred and six women at high risk of preterm labor had regular cervical monitoring by transvaginal ultrasound throughout pregnancy from the second trimester to delivery. The study was designed to be observational, but intervention was considered if the cervical length fell below 10 mm. RESULTS: Eleven women demonstrated opening of the cervical canal at rest or with fundal pressure before 24 weeks' gestation. Between 2 and 17 days later all 11 cervices progressively shortened to a cervical length of < 10 mm. Nine women had a cervical cerclage. Seven women had fetal membranes visible within the cervical canal at the time of cerclage. One woman miscarried at 18 weeks, and the other 10 had live births at a median gestational age of 36 (range, 27-38) weeks. CONCLUSIONS: Cervical length shortening in the second trimester, once started, progressed to a cervical length under 10 mm. Opening of the cervical os at rest or in response to fundal pressure detected by transvaginal ultrasound appears to be the early ultrasound feature of cervical incompetence.     

Cervical length and funneling at 23 weeks of gestation in the prediction of spontaneous early preterm delivery.

OBJECTIVES: To establish the relationship of cervical length at 23 weeks of gestation to the risk of spontaneous delivery before 33 weeks and to determine the possible additional risk if funneling is present. METHODS: During a 36-month period, 6819 women with singleton pregnancies underwent transvaginal sonographic cervical assessment at 22-24 weeks as a screening test for preterm delivery. The distribution of cervical length and the prevalence of funneling, defined as dilatation of the internal os of > or = 5 mm in width, were established. Women who underwent cervical cerclage, iatrogenic preterm delivery or were lost to follow-up were excluded from further analysis. In the remaining 6334 pregnancies, logistic regression was used to examine the contribution of cervical length and funneling to the risk of spontaneous preterm delivery before 33 weeks. RESULTS: The median cervical length was 36 mm and in 1.6% of cases the length was < or = 15 mm. There was a significant inverse association between cervical length and percentage rate of spontaneous delivery before 33 weeks. Funneling of the internal os was present in about 4% of pregnancies and the prevalence decreased with increasing cervical length from 98% when the length was < or = 15 mm to about 25% for lengths of 16-30 mm and less than 1% at lengths of > 30 mm. The rate of preterm delivery was 6.9% in those with funneling compared to 0.7% in those without funneling (chi2 = 86.7; P < 0.0001). However, logistic regression analysis demonstrated that funneling did not provide a significant additional contribution to cervical length in the prediction of spontaneous delivery before 33 weeks (odds ratio for short cervix = 24.9, Z = 4.43, P < 0.0001; odds ratio for funneling = 1.8, Z = 0.84, P = 0.40). CONCLUSION: In the prediction of preterm delivery, funneling does not provide any significant contribution in addition to cervical length.     

Cervical length for prediction of preterm birth in women with multiple prior induced abortions.

OBJECTIVE: To determine whether transvaginal sonographic cervical length predicts preterm birth in women with multiple prior induced abortions. METHODS: This was a retrospective cohort study using the Thomas Jefferson University Prematurity Database. Patients with a singleton pregnancy and a history of more than one induced abortion were identified. Exclusion criteria were cerclage and indicated preterm birth. Subjects were followed with transvaginal ultrasound measurement of the cervix between 14 and 24 weeks' gestation and grouped into those with and those without a short cervix; a cervical length of < 25 mm was considered short. The primary outcome was spontaneous preterm birth at < 35 weeks. RESULTS: Fifteen of the 65 (23%) women with more than one induced abortion included in the study had a short cervix. The demographics and risk factors were similar between those with and those without a short cervix. The overall incidence of preterm birth was 21.5% (14/65); in women with a short cervix the incidence was 47% (7/15) and in women without a short cervix it was 14% (7/50). The sensitivity, specificity and positive and negative predictive values of a short cervix in the prediction of preterm birth were 50%, 84%, 47% and 86%, respectively. The relative risk of a short cervix for spontaneous preterm birth was 3.3 (95% CI, 1.4-7.4). CONCLUSION: A cervical length of < 25 mm on transvaginal ultrasound is predictive of preterm birth in women with more than one prior induced abortion. Women with multiple prior induced abortions and a short cervix have a 3.3-fold greater chance of spontaneous preterm birth compared with those with a cervical length of > or = 25mm.     

Comparison of transperineal and transvaginal sonography in predicting preterm delivery

PURPOSE: A major advantage of transperineal sonography (TPUS) is its ability to evaluate the cervix without causing any distortion. This study was performed to compare transvaginal sonography (TVUS) and TPUS at 24 weeks of gestation in predicting preterm delivery in low-risk pregnancy. METHODS: Three hundred fifty-seven pregnant women underwent TVUS and TPUS at 24 weeks of gestation. The relationship between cervical length and preterm delivery was assessed. Accuracy values of TVUS and TPUS at 24 weeks of gestation were compared in predicting preterm delivery. RESULTS: Preterm delivery (before 36 weeks of gestation) occurred in 22 pregnancies (6.2%). Mean cervical lengths measured by TVUS and TPUS were significantly different in preterm and term delivery groups (P < 0.05). Areas under the curves were 0.801 and 0.857 for the transvaginal and transperineal measurements, respectively. The coefficient of correlation between the transvaginal and transperineal cervical length measurements was 0.83. TPUS had a sensitivity of 77% in predicting preterm delivery, with a false-positive rate of 17% and a relative risk of 4.5 at the 32.5-mm cutoff value. CONCLUSIONS: When the cervix is well visualized, TPUS can predict preterm delivery as accurately as TVUS.     

Translabial ultrasound of the third-trimester uterine cervix. Correlation with digital examination

This prospective blinded study compared translabial ultrasound (TLU) and digital palpation of the cervix among women whose cervix could not be visualized adequately or at all with transabdominal ultrasound during the third trimester of pregnancy. The cervical canal and internal cervical os were adequately visualized during 109 of 113 TLUs (96%). The TLU was well tolerated by the patients; only two patients refused the TLU pending discussion of the technique with their obstetrician. Among 43 examinations of patients without clinical cervical effacement, TLU showed a cervical length of 2.5 to 4.2 cm (mean, 2.9 cm). An excellent correlation (R = 0.90) was noted between cervical length on TLU and percentage of cervical effacement on digital examination. The correlation between amount of cervical dilatation on TLU and on digital examination was not high (R = 0.58). We conclude that the measurements of cervical length on TLU correlate well with the amount of cervical effacement on digital examination and that TLU provides a rapid and well-tolerated alternative technique to visualize the third-trimester uterine cervix.     

Clinical significance of placenta previa detected at early routine transvaginal scan.

Transvaginal ultrasonography in early pregnancy was used to determine the prevalence of placenta previa and the rate of persistence until delivery. The location of the placenta was registered systematically in 2342 pregnant women who underwent transvaginal ultrasonography at 10 to 16 weeks' gestation as a primary examination. The outcome of pregnancy as well as the presence or absence of placenta previa at delivery was noted in a total of 2158 cases. A receiver operating characteristic curve was generated for the different measurements from the edge of the placenta to the internal cervical os versus placenta previa at delivery. In 105 of the 2158 women screened in the early stages of pregnancy (4.9%) the placenta extended to or over the internal cervical os, and in 34 of 2158 patients (1.6%) the distance to the placental edge beyond the internal cervical os was equal to or greater than 14 mm. Of the eight cases of placenta previa at delivery, six (75%) were identified in our study, and two cases were missed. When a cutoff value of greater than 14 mm is used for the receiver operating characteristic curve the likelihood is 17.6% (95% confidence interval = 6.8 to 34.5) for placenta previa at delivery. Although a high percentage of false-positive results occur owing to the low prevalence at delivery, this screening procedure can identify high-risk patients who should be rescanned later in pregnancy.     

Sonographic imaging of cervical scars after Cesarean section.

OBJECTIVE: To investigate whether uterine contractions at the time of a Cesarean section have an impact on future presence and location of a cervical Cesarean scar. METHODS: A targeted transvaginal ultrasound examination of the fetus, uterus and cervix was done in 2973 consecutive women at 14-16 weeks' gestation. The sonographer was blinded to the women's previous obstetric histories. The presence and location of a sonographic cervical hypoechogenic line, which probably represented a Cesarean scar, was recorded. RESULTS: There were 180 women with a previous Cesarean section performed before the start of uterine contractions and 173 with a Cesarean section performed during contractions in labor. The cervical hypoechogenic line was more common in sections performed during contractions (75.7% vs. 52.7%; P < 0.001) and was more distally located from the internal os (17.9 +/- 9.4 vs. 14.6 +/- 9.1 mm; P = 0.01). A hypoechogenic line was observed in 21/2620 women without a previous Cesarean section, representing a false-positive rate of 0.8%. CONCLUSION: Cesarean sections, especially those done during uterine contractions, are actually performed through cervical tissue. This finding is in agreement with the physiological process of cervical effacement during contractions.     

Does transvaginal sonographic measurement of cervical length before 14 weeks predict preterm delivery in high-risk pregnancies?

OBJECTIVE: To determine whether high-risk patients manifest cervical length < 25 mm on transvaginal ultrasound before 14 weeks of gestation, and if this finding is predictive of preterm delivery. METHODS: Asymptomatic pregnancies at high risk for preterm birth were followed prospectively from 10 + 0 weeks to 13 + 6 weeks with transvaginal sonographic measurement of the cervix. A cervical length < 25 mm was considered a short cervix at this gestational age and at the follow-up ultrasound examinations, performed between 14 and 24 weeks. The primary outcome was preterm birth at < 35 weeks of gestation. RESULTS: One hundred and eighty-three pregnancies met the study criteria and were included in the analysis. Only 10 (5%) patients had a cervix < 25 mm before 14 weeks. The sensitivity, specificity and positive and negative predictive values of a short cervix were 14%, 97%, 50%, and 82%, respectively (relative risk, 2.8; 95% confidence interval, 1.4-5.6). The mean transvaginal sonographic cervical length before 14 weeks of gestation was 33.7 +/- 6.9 mm in pregnancies which delivered preterm (n = 36), and 35.0 +/- 6.8 mm in those delivering at term (n = 147) (P = 0.3). Follow-up transvaginal ultrasound examination of the cervix to 24 weeks revealed that the average gestational age at which a short cervix was detected was 18.7 +/- 2.9 weeks. CONCLUSION: A cervical length < 25 mm on transvaginal sonographic assessment rarely occurs before 14 weeks even in high-risk patients destined to deliver preterm; in these patients cervical changes predictive of preterm birth develop mostly after this gestational age.     

Vaginal ultrasound and cervical cerclage: a prospective study.

Vaginal ultrasound is a new technique for the objective assessment of the pregnant cervix. Twenty patients (21 pregnancies) were scanned at regular intervals throughout pregnancy after cervical cerclage by the vaginal route. Patients were recruited in 2 consecutive years in each of two centers with a low incidence of cervical cerclage (less than 0.5% of all pregnancies). Cervical cerclage, using Mersilene tape inserted by anterior and posterior incisions, positioned the cervical suture in the middle third of the cervical canal in all procedures (21/21). Ultrasound features including dilatation of the internal cervical os and herniation of the gestational sac to the level of the cervical suture were detected in 4/21 pregnancies at 5-7 weeks prior to delivery (21-33 weeks). Six patients (6/21) delivered preterm (< 37 weeks) without ultrasound features associated with cervical incompetence. Eleven patients (11/21) had a closed internal cervical os throughout pregnancy that remained closed after removal of the cervical suture at 38 weeks. In this study ultrasound features associated with cervical incompetence had a sensitivity of 40% and a specificity of 100% in the prediction of preterm pregnancy loss in this group of patients undergoing cerclage. Vaginal ultrasound is a simple, non-invasive technique that permits the detection of ultrasound features associated with cervical incompetence during pregnancy in patients who have had prophylactic cervical cerclage at 14-16 weeks' gestation. Ultrasound features associated with cervical incompetence were rare in this group of patients (4/21 from an overall obstetric population of 8000 deliveries) indicating a prevalence of cervical incompetence in the range of 1 : 1000-1 : 2000 deliveries. In the majority of patients undergoing cerclage (11/21) the clinical diagnosis of 'cervical incompetence' was incorrect as shown by the detection of a normal cervical canal following removal of the suture at 38 weeks.