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.     

Elective cerclage vs. ultrasound-indicated cerclage in high-risk pregnancies.

OBJECTIVE: To compare pregnancy outcome after elective vs. ultrasound-indicated cervical cerclage in women at high risk of spontaneous mid-trimester loss or early preterm birth. METHODS: This was a retrospective study comparing two management strategies in women with singleton pregnancies who had at least one previous spontaneous delivery at 16-33 weeks of gestation. One group was managed by the placement of an elective cerclage at 12-16 weeks and the other group had transvaginal ultrasound examinations of the cervix at 12-15+6, 16-19+6, and 20-23+6 weeks and cervical cerclage was carried out if the cervical length was 25 mm or less. RESULTS: A total of 90 patients were examined, including 47 that were managed expectantly and 43 treated by elective cerclage. In the expectantly managed group, 59.6% (28/47) required a cervical cerclage. We excluded from further analysis three patients who were lost to follow-up and three because of fetal death or iatrogenic preterm delivery. Miscarriage or spontaneous delivery before 34 weeks' gestation occurred in 14.6% (6/41) of the elective cerclage group, compared with 20.9% (9/43) in the expectantly managed group (chi2 = 0.219, P = 0.640). CONCLUSION: In women at increased risk of spontaneous mid-trimester or early preterm delivery, a policy of sonographic surveillance followed by cervical cerclage in those with a short cervix reduces the need for surgical intervention without significantly increasing adverse pregnancy outcome.     

Cervical Incompetence Prevention Randomized Cerclage Trial (CIPRACT): effect of therapeutic cerclage with bed rest vs. bed rest only on cervical length.

OBJECTIVE: To compare the effects of therapeutic cerclage and bed rest vs. just bed rest on cervical length and to relate these effects to the risk of preterm delivery. DESIGN: Cervical length was measured in patients at high risk of cervical incompetence. When a cervical length < 25 mm was measured before 27 weeks' gestation, randomization for therapeutic cerclage and bed rest vs. just bed rest was performed. After randomization, cervical length was measured weekly. For statistical analysis, t-test and Fisher's exact tests were used and P < 0.05 was considered statistically significant. RESULTS: Nineteen women were randomly allocated to receive a therapeutic cerclage and bed rest and 16 were allocated to receive bed rest only. Mean cervical lengths and mean gestational ages before randomization were comparable between both groups, overall 19.8 mm and 20.7 weeks. Cervical length was measured again at a mean gestation of 22.1 weeks. Mean cervical length (31 mm) was significantly (P < 0.0001) longer after cerclage than after bed rest only (19 mm). A cervical length > or = 25 mm was measured in 22 of the 35 included women, 16 in the cerclage group and six in the bed-rest group (P = 0.006). Of these 22 women, only one delivered before 34 weeks' gestation, which was significantly less frequent than six out of 13 women with a cervical length < 25 mm (P = 0.006). CONCLUSIONS: Therapeutic cerclage with bed rest increases cervical length more often than bed rest alone. A postintervention cervical length > or = 25 mm reduces the risk of preterm delivery in women at high risk of cervical incompetence and a preintervention cervical length < 25 mm.     

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.     

Cervical length at 11-14 weeks' and 22-24 weeks' gestation evaluated by transvaginal sonography, and gestational age at delivery.

OBJECTIVE: To compare cervical length measurements obtained at 11 to 14 weeks and 22 to 24 weeks of gestation in an unselected group of pregnant women and to correlate the measurements with time of delivery. METHODS: This was a prospective study involving 529 pregnant women attending for routine antenatal care who underwent transvaginal scans at 11-14 weeks and 22-24 weeks for evaluation of cervical length. The mean cervical length was calculated at both stages of gestation and lengths were compared between groups which delivered at term or prematurely, this being defined as delivery before 37 completed weeks of gestation. RESULTS: The mean cervical lengths at 11-14 and 22-24 weeks were, respectively, 42.4 mm and 38.6 mm. Cervical length at 11-14 weeks was not significantly different between the groups which delivered at term (42.7 mm) and preterm (40.6 mm). However, at the 22-24-week evaluation, cervical length was significantly shorter in the group which had a preterm delivery than in that which had a term delivery (26.7 mm and 39.3 mm, respectively; P = 0.0001). In the group of women with a previous history of one or more preterm deliveries, there was a greater shortening in cervical length from the first to the second evaluation than there was in the group of women with no previous history of preterm delivery. This shortening was also more pronounced in the group which delivered prematurely (from 40.6 mm to 26.7 mm) than in that which delivered at term (from 42.7 mm to 39.3 mm). CONCLUSION: There is a spontaneous shortening in the pregnant cervix from the first to the second trimester of pregnancy. The shortening is more rapid in pregnant women who deliver prematurely and who have a history of previous preterm delivery.     

Sonographic cervical length in singleton pregnancies with intact membranes presenting with threatened preterm labor.

OBJECTIVE: Less than 10% of women presenting with preterm contractions progress to active labor and delivery. This study investigates whether cervical length measurements by ultrasound can discriminate between true and false labor in women presenting with threatened preterm labor. METHODS: Cervical length was measured by transvaginal ultrasound in 253 women with singleton pregnancies presenting with painful uterine contractions at a median age of 31 (range, 24-35) weeks of gestation. Women presenting in active labor, defined by the presence of cervical dilatation of >or = 3 cm, those with ruptured membranes and those that underwent prior or subsequent cervical cerclage were excluded from the study. The clinical management was determined by the attending obstetrician without taking into account the cervical length. Primary outcome of the study was delivery within 7 days of presentation based on the results of randomized studies on the use of tocolytics in women with preterm labor that reported a prolongation of pregnancy by 7 days. RESULTS: Delivery within 7 days of presentation occurred in 21/253 (8.3%) pregnancies and this was inversely related to cervical length. Receiver-operating characteristics (ROC) curves established a cervical length of 15 mm as the most relevant cut-off level for the prediction of preterm delivery within 7 days. In 217 cases the cervical length was > or = 15 mm and only four of these (1.8%) delivered within 7 days. In the 36 women with cervical length < 15 mm, delivery occurred in 17 (47.2%) within 7 days. Logistic regression analysis demonstrated that significant independent contribution in the prediction of delivery within 7 days was provided by cervical length, contraction frequency at presentation, previous history of preterm delivery and vaginal bleeding. There was no significant contribution from gestation at presentation, ethnic origin, maternal age, parity, cigarette smoking or the administration of tocolysis, antibiotics or steroids. Similar results were shown in a subanalysis of 162 patients presenting at a gestational age below 32 weeks: 9/19 patients (47.4%) with a cervical length below 15 mm delivered within 7 days compared to 3/143 (2.1%) with a cervical length > or = 15 mm. Univariate as well as multivariate analyses confirmed cervical length to be a significant independent predictor of delivery within 7 days in this population. CONCLUSIONS: Sonographic measurement of cervical length helps to avoid overdiagnosis of preterm labor in women with preterm contractions and intact membranes.     

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.     

Funneling to the stitch: an informative ultrasonographic finding after cervical cerclage.

OBJECTIVE: The purpose of this study was to evaluate the utility of ultrasound surveillance after cerclage placement and to propose a rationale for cervical sonography in this setting. SUBJECTS AND METHODS: This was a retrospective analysis of 53 women undergoing cervical cerclage by a maternal-fetal medicine specialist, regardless of indication, and delivering between January 1999 and April 2001. Transvaginal ultrasonographic assessment of cervical length and the degree of cervical funneling after cerclage were compared to preoperative values and to outcomes including gestational age at delivery. Funneling to the cerclage was defined as membranes prolapsing down the endocervical canal until they reached the plane of the cerclage. RESULTS: Cervical cerclage resulted in a significant increase in cervical length from 2.1 +/- 1.2 cm to 2.9 +/- 0.8 cm after the procedure, P < 0.001; however, this measure was not correlated with gestational age at delivery. Funneling to the level of the cerclage was associated with an earlier gestational age at delivery 31.3 +/- 5.6 weeks vs. 36.8 +/- 2.8 weeks for those cases without this finding, P < 0.001. A statistically significant association between funneling to the cerclage and preterm delivery was identified irrespective of the indication (prophylactic or emergency) for the procedure. When descent of the membranes to the level of the cerclage was noted, it occurred by 28 weeks' gestation in all patients studied. The incidence of premature rupture of the membranes was also significantly greater postcerclage in women with descent of the membranes to the cerclage (52%) compared to those without this finding (9%) P= 0.002. CONCLUSIONS: Funneling to the cerclage is significantly associated with earlier preterm delivery in patients who have undergone cervical cerclage. Serial sonography up to 28 weeks' gestation is useful in identifying patients at higher risk for premature rupture of the membranes and preterm delivery.     

Transvaginal ultrasonographic measurement of cervical length as a predictor of preterm birth: a systematic review with meta-analysis

The advent of effective interventions to prevent preterm delivery such as 17 hydroxyprogesterone and cerclage serve as an impetus to determine whether routine second trimester transvaginal cervical length screening can identify which women would benefit from these therapies. A systematic review was conducted, 957 abstracts were screened, 234 articles underwent full-text review, and 23 studies were included in the final analysis including 26,792 women. Data from relevant studies were pooled to produce summary estimates of sensitivity, specificity, and likelihood ratios using a random effects model. The ideal criteria of transvaginal cervical length measurements to predict preterm delivery are discussed.     

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.     

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。     

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.     

Does transvaginal ultrasound of the cervix predict preterm premature rupture of membranes in a high-risk population?

OBJECTIVES: To determine in patients with a cervical length < 25 mm on transvaginal ultrasound if the severity of cervical length shortening can be used to predict preterm premature rupture of membranes (PPROM) and the contribution of PPROM to preterm delivery in these patients. METHODS: We retrospectively reviewed asymptomatic singleton pregnancies between 14 and 24 weeks at high risk of preterm delivery by obstetric history and transvaginal cervical length < 25 mm. Cases developing subsequent PPROM were compared with controls for transvaginal sonographic cervical characteristics. RESULTS: Of 69 patients identified to have a cervical length < 25 mm, 27 (39%) had PPROM, and 42 (61%) did not. Mean +/- standard deviation (SD) cervical length was 12.7 +/- 8.7 mm and 17.0 +/- 7.6 mm in the two groups, respectively (P = 0.04). Mean +/- SD cervical funneling was 57.4 +/- 31.4% and 40.0 +/- 28.1%, respectively (P = 0.01). The characteristics most predictive of PPROM were: cervical length of < 10 mm (sensitivity, specificity, positive and negative predictive values of 33, 90, 69, and 68%, respectively; odds ratio, 4.8; 95% confidence interval, 1.3-17.5) and cervical funneling > 75% (sensitivity, specificity, positive and negative predictive values of 33, 93, 75 and 68%, respectively; odds ratio, 6.5; 95% confidence interval, 1.6-26.9). Stepwise logistic regression revealed cervical length to be a significant predictor of PPROM (odds ratio, 4.0; 95% confidence interval, 1.1-14.2). CONCLUSION: In patients at high risk for preterm delivery because of obstetric history and transvaginal sonographic cervical length < 25 mm, a cervical length < 10 mm and cervical funneling > 75% were most predictive of PPROM. PPROM was the major contributor to preterm delivery in these patients.     

Prediction of preterm birth by second trimester cervical sonography in twin pregnancies.

OBJECTIVES: To determine the predictive value of sonographic cervical length and of funneling for spontaneous preterm delivery (PTD) in twin pregnancies under 26 weeks' gestation. METHODS: Women with twin pregnancies were studied prospectively with transvaginal or translabial ultrasound of the cervix from 18 to 26 weeks' gestation. Exclusion criteria were: signs of preterm labor, prophylactic cervical cerclage, placenta previa, or severe congenital fetal anomaly. The primary outcome was spontaneous preterm birth at < 35 weeks' gestation. RESULTS: Sixty-five twin pregnancies were analyzed, of which 23% (15/65) delivered preterm. Cervical ultrasound examination was performed by 22 weeks' gestation in 75% and by 24 weeks' gestation in 91% of women. Cervical length < or = 25 mm and < or = 30 mm was associated with sensitivities of 27% and 53%, respectively, and with 67% and 62% rates of PTD, respectively (R.R. 4.6, C.I. 2.0-10.3 and R.R. 3.6, C.I. 1.6-7.8, respectively). A cervical length > 35 mm was associated with only a 4% rate of PTD (R.R 0.13; C.I. 0.02-0.93). Of 10 women (15%) with any cervical funneling, 70% delivered preterm, all under 32 weeks' gestation. By logistic regression analysis, both short cervix < or = 30 mm and any funneling were strongly predictive of PTD. CONCLUSIONS: Both cervical length < or = 30 mm and cervical funneling in twin pregnancies under 26 weeks' gestation are independently and strongly associated with high risk for preterm birth. A long cervix, of length > 35 mm, is associated with very low risk (4%) for preterm birth.     

Early prediction of preterm delivery by transvaginal ultrasonography.

The clinical value of transvaginal ultrasonography in the evaluation of the uterine cervix of pregnant women was studied. Comparison with conventional transabdominal ultrasound in 24 pregnant subjects revealed that transvaginal ultrasound was superior, because the transabdominal technique usually requires a full bladder, which causes deformation and elongation of the cervix. Digital examination showed dilatation of the internal os in only ten (38.5%) of 26 patients in whom it had previously been shown by transvaginal sonography. Transvaginal ultrasonography has the advantage of providing natural and objective information on the cervix. The values of three sonographic signs found transvaginally for predicting preterm delivery were evaluated in a total of 130 at-risk patients and 129 control subjects. Shortening of the cervical length by -1.5 SD or more was associated with an increased risk of preterm delivery (11.3% vs. 2.8%, p < 0.01). A dilated internal os of more than 5 mm before 30 weeks of gestation was associated with preterm delivery more often than an undilated internal os (33.3% vs. 3.5%, p < 0.01). Dynamic changes in the degree of dilatation of the cervical canal which were found in nine women were significantly related with preterm delivery (p < 0.05). But, in the at-risk group, only dilatation of the internal os had a predictive value for preterm birth. From these data, dilatation of the internal os on transvaginal ultrasonography was proved to be an early and important predictor of preterm delivery.     

Sonographic measurement of cervical length in twin pregnancies in threatened preterm labor.

OBJECTIVE: To determine whether sonographic measurement of cervical length in twin pregnancies presenting with threatened preterm labor helps distinguish between true and false labor. METHODS: In 87 women with twin pregnancies presenting with regular and painful uterine contractions at 24-36 (median, 30) weeks of gestation, cervical length was measured by transvaginal ultrasound. Women presenting in active labor, defined by the presence of cervical dilation of 3 cm or more, with ruptured membranes and those who underwent a prior or subsequent cervical cerclage, were excluded from the study. The clinical management was determined by the attending obstetrician without taking into account the cervical length. Primary outcome of the study was delivery within 7 days of presentation. RESULTS: Delivery within 7 days of presentation occurred in 19/87 (22%) pregnancies and this was inversely related to cervical length, decreasing from 80% (4/5) at 1-5 mm, to 46% (6/13) at 6-10 mm, 29% (4/14) at 11-15 mm, 21% (4/19) at 16-20 mm, 7% (1/15) at 21-25 mm and 0% (0/21) at >25 mm. Logistic regression analysis demonstrated that significant independent contribution in the prediction of delivery within 7 days was provided by cervical length (odds ratio (OR) = 0.78, 95% CI 0.68-0.89, P < 0.001) and use of tocolytics (OR = 0.13, 95% CI 0.02-0.76, P = 0.024), with no significant contribution from gestation at presentation, chorionicity, ethnic origin, maternal age, body mass index, parity, previous history of preterm delivery, cigarette smoking, contraction frequency, vaginal bleeding or the administration of antibiotics or steroids. CONCLUSION: In women with twin pregnancies presenting with threatened preterm labor, sonographic measurement of cervical length helps distinguish between those who deliver within 7 days and those who do not.     

Prediction of preterm delivery in twin pregnancy: a prospective, observational study of cervical length and fetal fibronectin testing.

OBJECTIVE: To evaluate prospectively cervical length measurements and fetal fibronectin detection as predictors of spontaneous preterm delivery in an unselected population of twin pregnancies. METHODS: Transvaginal ultrasound assessments of cervical length were performed serially at 18, 24, 28 and 32 weeks' gestation. Receiver-operating characteristic curves were generated at each time point to determine the optimal cut-off for cervical length and rate of change in cervical length in the prediction of preterm delivery (< 35 weeks). A bedside assay for the detection of fetal fibronectin in the maternal vaginal secretions was performed prior to cervical length measurements from 24 weeks. Likelihood ratios (LRs) were used to assess the performance of each test. RESULTS: The spontaneous preterm delivery rate was 16.5% in 91 studied twin pregnancies. A cervical length /= 2.5 mm per week between 18 and 28 weeks' gestation also predicted preterm delivery (LR+ 10.8, sensitivity 16.7%). There was no relationship between the detection of fetal fibronectin and preterm delivery. CONCLUSIONS: This study confirms the value of transvaginal ultrasound assessment of cervical length as a predictor of preterm delivery in twin pregnancies. However, the poor sensitivity of this test makes it unsuitable as a single predictor of preterm delivery. Fetal fibronectin testing does not identify twin pregnancies destined to deliver prematurely.     

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 length evaluation by transvaginal sonography in nongravid women with a history of preterm delivery.

OBJECTIVE: To evaluate cervical length in the nongravid period in women with a past history of preterm delivery. METHODS: The study population comprised 54 women who had delivered spontaneously before 34 weeks of gestation. Etiology of preterm delivery was suspected to be related to cervical incompetence, defined as a painless and progressive dilatation of the cervix in the absence of other causes. Patients with pre-eclampsia, intrauterine growth restriction, uterine anomalies, fetal anomalies, multiple gestation and similar complications were excluded. Shortening of the cervix was recorded during pregnancy in all study patients. One hundred and four women matched for age, parity and body mass index who had given birth at term served as the control group. Cervical length was evaluated in all women at least 12 weeks after delivery by transvaginal sonography in the mid-sagittal plane. RESULTS: The mean gestational age at delivery was 30.8 +/- 1.2 weeks in the study group and 38.8 +/- 2.1 weeks in the control group (P = 0.03). The mean cervical length in the two groups was 36 +/- 6 and 38 +/- 4 mm, respectively. This difference was not statistically significant (P = 0.9). CONCLUSIONS: In nongravid women with unexplained preterm delivery there is no difference in cervical length compared to patients who deliver at term. Shortening of the cervix is most probably a reversible phenomenon that occurs during pregnancy and represents a failure of the competence mechanism to adapt to pregnancy.     

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.