Comparative longitudinal study of cervical length and induced shortening changes among singleton, twin, and triplet pregnancies

Differences in cervical length during the second trimester among normal weight, overweight and obese women: A systematic review and meta-analysis

Objective

Maternal obesity has been previously linked to increased risk of preterm birth; however, the actual pathophysiology behind this observation remains unknown. Cervical length seems to differentiate among overweight, obese and extremely obese patients, compared to normal weight women. However, to date the actual association between body mass index and cervical length remains unknown. In this systematic review, accumulated evidence is presented to help establish clinical implementations and research perspectives.

Methods

We searched Medline, Scopus, the Cochrane Central Register of Controlled Trials CENTRAL, Google Scholar, and Clinicaltrials.gov databases from inception till February 2023. Observational studies that reported on women undergone ultrasound assessment of their cervical length during pregnancy were included, when there was data regarding their body mass index. Statistical meta-analysis was performed with RStudio. The quality of the included studies was assessed using the Newcastle-Ottawa Quality Assessment Scale (NOS).

Results

Overall, 20 studies were included in this systematic review and 12 in the meta-analysis. Compared to women with normal weight, underweight women were not associated with increased risk of CL < 15 mm or < 30 mm and their mean CL was comparable (MD -1.51; 95% CI -3.07, 0.05). Overweight women were found to have greater cervical length compared to women with normal weight (MD 1.87; 95% CI 0.52, 3.23) and had a lower risk of CL < 30 mm (OR 0.65; 95% CI 0.47, 0.90).

Conclusion

Further research into whether BMI is associated with cervical length in pregnant women is deemed necessary, with large, well-designed, prospective cohort studies with matched control group.

Ultrasound-Indicated Cerclage in Twin Pregnancies: A Cohort Study

Background

To report the pregnancy and neonatal outcomes in patients with twin pregnancies who underwent ultrasound-indicated cerclage (UIC) and to compare them to patients with singleton pregnancies undergoing the same procedures.

Methods

Patients who underwent UIC between January 2010 and December 2020 at Kangnam Sacred Heart Hospital were reviewed. We compared characteristics, pregnancy, and neonatal outcomes between patients with singleton and twin pregnancies.

Results

A total of 94 women (56 singleton and 38 twin pregnancies) underwent UIC were included. The mean gestational age (GA) at cerclage and preoperative cervical length (CL) were not significantly different. Twin pregnancies were more likely to deliver at earlier median gestations than singletons (singleton, 36 + 1 weeks vs twin, 32 + 6 weeks, and p = 0.004). The frequency of preterm delivery <34 weeks in twin group was higher than in singleton group (15 (26.8%) vs 20 (52.6%) and p =0.016). However, the frequency of preterm delivery <32, <28, and <24 weeks was not significantly different between two groups. Although neonatal weights in singleton pregnancies were heavier than twin pregnancies, neonatal mortality and morbidities were not significantly different between two groups. Among various factors contributing to preterm birth, preoperative CL ≤ 15 mm was independently associated with a higher risk of preterm delivery before 34 weeks. Furthermore, pregnancy and neonatal outcomes of twin pregnancies with cervical length ≤ 15 mm are comparable with those of singleton pregnancies (GA at delivery, singleton, 35 + 1 weeks vs twin, 32 + 5 weeks, and p = 0.24; neonatal mortality, singleton, 3.4% vs twin, 4.8%, and p = 0.64).

Conclusion

The pregnancy and neonatal outcomes of UIC in twin pregnancies were comparable to those in singleton pregnancies, especially when CL is ≤15 mm. UIC might be considered a safe procedure for twin pregnancies.

Labour induction in twin pregnancies

Medically-indicated deliveries are common in twin pregnancies given the increased risk of various obstetric complications in twin compared to singleton pregnancies, mainly hypertensive disorders of pregnancy and foetal growth restriction. Due to the unique characteristics of twin pregnancies, the success rates and safety of labour induction may be different than in singleton pregnancies. However, while there are abundant data regarding induction of labour in singleton pregnancies, the efficacy and safety of labour induction in twin pregnancies have been far less studied. In the current manuscript we summarize available data on various aspects of labour induction in twin pregnancies including incidence, success rate, prognostic factors, safety and methods for labour induction in twins. This information may assist healthcare providers in counselling patients with twin pregnancies when labour induction is indicated.

Uterine Cervical Change at Term Examined Using Ultrasound Elastography: A Longitudinal Study

The aim of the study was to investigate if there are changes in elastographic parameters in the cervix at term around the time of delivery and if there are differences in the parameters between women with spontaneous labor and those without labor (labor induction). Nulliparous women at 36 weeks of gestation eligible for vaginal delivery were enrolled. Cervical elastography was performed and cervical length were measured using the E-Cervix^TM system (WS80A Ultrasound System, Samsung Medison, Seoul, Korea) at each weekly antenatal visit until admission for spontaneous labor or labor induction. E-Cervix parameters of interest included elasticity contrast index (ECI), internal os strain mean level (IOS), external os strain mean level (EOS), IOS/EOS strain mean ratio, strain mean level, and hardness ratio. Regression analysis was performed using days from elastographic measurement at each visit to admission for delivery and the presence or absence of labor against cervical length, and each E-Cervix parameter fitted to a linear model for longitudinal data measured repeatedly. A total of 96 women were included in the analysis, (spontaneous labor, n = 39; labor induction, n = 57). Baseline characteristics were not different between the two groups except for cesarean delivery rate. Cervical length decreased with advancing gestation and was different between the two groups. Most elastographic parameters including ECI, IOS, EOS, strain mean, and hardness ratio were significantly different between the two groups. In addition, ECI, IOS, and strain mean values significantly increased with advancing gestation. Our longitudinal study using ultrasound elastography indicated that E-cervix parameters tended to change linearly at term near the time of admission for delivery and that there were differences in E-Cervix parameters according to the presence or absence of labor.

Does late second-trimester cervical length predict unscheduled preterm birth in asymptomatic triplet pregnancies?

OBJECTIVE

Multiple gestation increases the risk of unscheduled preterm birth (PTB), both spontaneous and indicated, leading to increased neonatal morbidity and additional healthcare costs. The purpose of this study was to determine whether cervical length (CL) assessment by 28 weeks could predict unscheduled PTB <34 weeks in triplet pregnancies. Secondary outcomes included prediction of PTB <30 weeks, prediction of PTB based on degree of cervical change and effect of ART-use on PTB.

METHODS

This was a retrospective cohort of women with triplet pregnancies. The exposure variable of interest was short cervix < 25 and <20 millimeters (mm) by 28 weeks. Maternal characteristics were described. The distribution of CLs was analyzed by the primary outcome of unscheduled PTB < 34 weeks, and by PTB <30 weeks (secondary outcome). Gestational age at delivery was compared between women with and without a short cervix. Changes in CL were compared between the groups with unscheduled PTB and those delivering ≥34 and ≥30 weeks. Statistical analyses were performed using appropriate tests.

RESULTS

Of 92 triplet pregnancies, 51 met the criteria, with 1233 total (411 shortest) CL measurements from 16 to 34 weeks' gestation. The overall rate of PTB <34 weeks was 31.4% and <30 weeks was 9.8%. The median gestational age at delivery was 32.7 (IQR 2.3) weeks. There were no statistically significant differences in rates of unscheduled PTB in women who had a short cervix and those that did not: PTB <34 weeks with CL <25 mm (p = .53) and CL <20 mm (p = .70); PTB <30 weeks with CL <25 mm (p = .38) and CL <20 mm (p = .26). The degree of cervical change from 18 to 28 weeks was not statistically significant for predicting unscheduled PTB <34 and <30 weeks. Of 70.6% of triplet pregnancies conceived by ARTs, 13.9% had unscheduled PTB <30 weeks, whereas no spontaneously-conceived pregnancies delivered <30 weeks (p = .14).

CONCLUSION

Short cervix did not predict unscheduled spontaneous PTB <34 weeks nor <30 weeks in our triplet cohort, nor did the degree of cervical change by 28 weeks predict PTB. Triplets conceived by ARTs may have an increased risk of unscheduled PTB.

Changes in the perinatal outcomes of twin pregnancies delivered at a tertiary referral center in Korea during a 24-year period from 1995 to 2018

Objective

To analyze the changes in the clinical characteristics and perinatal outcomes of twin pregnancies delivered at a tertiary referral center in Korea during a 24-year period.

Methods

This was a retrospective cohort study of twin pregnancies delivered at 24–40 weeks of gestation, from 1995 to 2018. The subjects were divided into 4 groups according to the year of delivery: 1995–2000, 2001–2006, 2007–2012, and 2013–2018. The trends in the changes in the twin birth rate, maternal age, assisted reproductive technology (ART) pregnancy rate, chorionicity, obstetric complications, delivery outcomes, and neonatal outcomes over the periods were analyzed.

Results

A total of 2,133 twin pregnancies were included in the study. The twin birth rate increased from 16.7/1,000 in 1995–2000 to 42.2/1,000 in 2001–2006, 49.5/1,000 in 2007–2012, and 61.8/1,000 in 2013–2018. The maternal age and ART pregnancy and dichorionic twin rates increased, while the monochorionic twin rate decreased over the periods. The incidence of fetal congenital anomalies, cervical incompetence, gestational diabetes mellitus, preeclampsia, and placental abruption increased over the periods. The preterm birth (PTB) rate significantly decreased owing to the decreasing elective late-PTB rate; however, the early-PTB rate significantly increased.

Conclusion

This study found that twin pregnancies increased steadily over the last 24 years and that the increase was related to increased maternal age and ART pregnancy rate. The incidence of obstetric complications increased over the periods; however, the neonatal intensive care unit admission rate decreased, along with decreases in the elective late-PTB rate.

Prediction of preterm birth and adverse perinatal outcomes after cervical pessary placement in singleton pregnancies with short cervical length

OBJECTIVES

To identify ultrasound-assessed cervical characteristics, modified after pessary placement, which could be predictive of spontaneous preterm birth (sPTB) at < 34 weeks of gestation (WG) or severe adverse perinatal outcomes (APO).

STUDY DESIGN

This prospective observational study conducted at Vall d'Hebron Universitary Hospital assessed multiple cervical characteristics in women with short cervical length (CL). All participants were examined by transvaginal ultrasound before and immediately after a cervical pessary was placed. Cervical assessment included CL, uterocervical angles (UCA), and cervical consistency indexes (cervical consistency index (CCI) and cervical length consistency index (CLCI)). Pregnancy outcomes were recorded to determine the capacity of these variables for predicting sPTB at < 34 WG and severe APO.

RESULTS

Thirty-one women with short CL, 17 (54.8%) with asymptomatic midtrimester short CL, and 14 (45.2%) after arrested threatened preterm labor were enrolled. After pessary placement, transvaginal ultrasound detected four participants in whom the pessary was not correctly placed around the cervix (12.9%); additionally, significant changes were observed in most cervical baseline characteristics, with CL, anterior UCA (A-UCA), CLCI, and intersegmentary angle (ISA) being predictive of sPTB at <34 WG and severe APO. Receiver operator curves were calculated to compare the predictive capacity of these variables, with CL and A-UCA after pessary placement being the best predictive parameters with an area under the curve of 0.88 and 0.87, respectively.

CONCLUSIONS

Transvaginal ultrasound after pessary placement detects incorrect pessary placement after pessary insertion and during follow-up. APO and sPTB can be predicted by measuring CL, A-UCA, CLCI, and ISA immediately after pessary placement, being CL and A-UCA more accurate and easier to be measured. Our results help to better identify women in whom the pessary is more likely to fail. Further research is required to assess the effectiveness of applying alternative, sequential or additional treatments to reduce prematurity and our results could be considered when designing such studies.

Cervical modifications after pessary placement in singleton pregnancies with maternal short cervical length: 2D and 3D ultrasound evaluation

INTRODUCTION

The use of a pessary proved to prevent preterm birth in asymptomatic women with mid-trimester short cervical length (CL); however, the precise mechanisms by which the pessary confers its benefit remain unclear. The aim of this study was to evaluate multiple cervical characteristics assessed by 2-dimensional and 3-dimensional ultrasound before and after placement of a cervical pessary to ascertain its mechanism of action.

MATERIAL AND METHODS

In this prospective cohort study, we assessed the cervical characteristics in singleton pregnancies with maternal short CL and compared them with matched reference women with normal CL. The variables evaluated were: CL, uterocervical angles, cervical consistency indices (cervical consistency index and CL consistency index), cervical volume and vascular indices. All variables were re-assessed immediately after pessary placement and 4-6 weeks later in all participants. Mann-Whitney U test was used to assess differences between groups and paired samples t test for comparisons in two different examinations in the same women. The aim of this study was to evaluate multiple cervical ultrasound variables before and after the placement of a cervical pessary and compare the evolution of these variables with a reference group with normal CL to better understand the device's mechanism of action.

RESULTS

Thirty-three women with short CL and 24 reference women with normal CL were enrolled. At the time of enrollment, gestational age and maternal baseline characteristics did not differ between groups. Immediately after pessary placement, CL increased, uterocervical angles were narrower and cervical consistency increased significantly. When the magnitude of change in cervical variables was compared over time between the reference group and the study group, median CL had increased in the study group (1.47 mm) but it had shortened in the reference group (-2.56 mm). These inverse trends were statistically significant (P = 0.006).

CONCLUSIONS

Cervical pessary reduces both uterocervical angles and corrects cervical angulation by pushing the cervix up toward the uterus. Maintaining the cervix aligned to the uterine axis leads to reduced cervical tissue stretch, so avoiding further cervical shortening. All these changes were present after pessary placement; however, the clinical implications of these findings remain unknown.

Outcomes of physical examination-indicated cerclage in twin pregnancies with acute cervical insufficiency compared to singleton pregnancies

Objectives To compare pregnancy outcomes of physical examination-indicated cerclage in twin pregnancies with acute cervical insufficiency with that of singletons. Methods This retrospective cohort study included 88 consecutive women (17 twins and 71 singletons) who had undergone physical examination-indicated cerclage because of acute cervical insufficiency (defined as painless cervical dilation with (1) prolapsed and/or visible membranes at the external cervical os on speculum examination and (2) a functional cervical length of zero on transvaginal ultrasound) between 160/7 and 236/7 weeks. The primary outcome measure was preterm delivery <34 weeks. Results (1) The frequency of preterm delivery <34 weeks was not significantly different between the two groups [twins, 56% (9/16) vs. singleton, 53% (37/70), P>0.999]. (2) The perinatal mortality was 21% (7/34) in twins and 32% (23/71) in singletons. (3) The median gestational age at delivery for twin pregnancies was 31.0 weeks (IQR, 22.6-36.5 weeks), which was similar to that of singleton pregnancies (median 32.4 weeks; IQR 22.3-38.3 weeks). (4) There were no significant differences in preterm delivery before 28 and 32 weeks, interval from cerclage to delivery within 1, 2, 4 and 8 weeks and neonatal morbidities between the two groups. Conclusion The obstetric and neonatal outcomes of physical examination-indicated cerclage in twin pregnancies were comparable to those in singleton pregnancies.

Cervical length dynamics in triplet pregnancies: a retrospective cohort study

Purpose

To review our experience with a screening program that included sequential cervical length measurements in our large population of triplet pregnancies.

Methods

Seventy-eight triplet pregnancies were retrospectively included. Cervical length measurements were performed by transvaginal ultrasound in 2-week intervals from week 16 + 0 onwards in a tertiary-care center in Vienna. The main outcome measurement was preterm delivery prior to 32 + 0 weeks of gestation. Statistical analyses were performed using paired and unpaired t tests and a stepwise linear regression model.

Results

There were 26 cases of preterm delivery (33.3%). Women with preterm delivery revealed significant cervical length shortening from week 22 + 0 (median 33 mm, interquartile range, IQR 17–39) to 24 + 0 (median 21 mm, IQR 7–30; p = 0.005). This was not observed in women without preterm delivery. From week 22 + 0 onwards, both groups showed further significant 2-week differences in cervical length (p < 0.05). Univariate analysis of cervical length in weeks 20 + 0, 22 + 0, and 24 + 0 as well as cervical length dynamics from 22 + 0 to 24 + 0 predicted preterm delivery.

Conclusions

In triplet pregnancies, a decrease in cervical length seems physiological from week 22 + 0 onwards. A sharp decrease in cervical length from the 22 + 0 to the 24 + 0 week as well as the smaller cervical length in weeks 20 + 0, 22 + 0, and 24 + 0 increase the risk of preterm delivery.

Short cervical lengths initially detected in mid-trimester and early in the third trimester in asymptomatic twin gestations: Association with histologic chorioamnionitis and preterm birth

Objective

To determine whether short cervical lengths (≤20 mm) that were initially detected in mid-trimester and early in the third trimester are independently associated with increased risks of subsequent histologic chorioamnionitis and spontaneous preterm birth (SPTB, defined as a delivery before 34 weeks) in asymptomatic women with twin pregnancies.

Material and methods

This is a prospective study including 292 consecutive asymptomatic women with twin gestations. Cervical length measurements were carried out at 20 to 24 weeks’ gestation and at 28 to 32 weeks’ gestation. Both placentas of each twin pair were examined histologically after delivery. The generalized estimation equations models and logistic regression analysis were used for statistical analyses.

Results

Multivariable generalized estimation equations analysis revealed that short cervical length at mid-trimester was independently associated with an increased risk for subsequent histologic chorioamnionitis, whereas short cervical length initially detected early in the third trimester was not. By using the likelihood of SPTB as an outcome variable, multivariable logistic regression analysis indicated that short mid-trimester cervical length and histologic chorioamnionitis were independently associated with a greater risk for SPTB. Similarly, based on the multivariable analysis, a short third trimester cervical length was independently and significantly associated with a greater risk for SPTB.

Conclusions

In asymptomatic women with twin pregnancies, a short mid-trimester cervical length is independently associated with an increased risk of both subsequent histologic chorioamnionitis and SPTB, whereas a short cervical length initially detected early in the third trimester is independently associated with preterm delivery, but not subsequent histologic chorioamnionitis.

The greater risk of preterm birth in triplets is mirrored by a more rapid cervical shortening along gestation

BACKGROUND

The risk of preterm birth increases with plurality. However, data are limited about the role of cervical length in triplet pregnancies and how the greater predisposition for preterm birth in triplet pregnancies, compared with twin pregnancies, is reflected by cervical length. Specifically, it is unclear whether the greater predisposition of triplet pregnancies for preterm birth is reflected by a more rapid cervical shortening during gestation compared with twin pregnancies (and therefore a shorter cervical length at any given gestational age), by a greater risk for preterm birth per given cervical length at any given gestational age, or both.

OBJECTIVE

The purpose of the study was to compare the rate of cervical shortening during gestation and the correlation between cervical length and gestational age at birth in asymptomatic women with triplet vs twin pregnancies.

STUDY DESIGN

This was a retrospective study of women with triplet or twin pregnancies who were who were observed in a tertiary center who underwent serial sonographic measurement of cervical length from 16-32 weeks gestation. Change in cervical length during gestation and relationship of cervical length with gestational age at birth were compared between the triplets and twins groups.

RESULTS

A total of 431 measurements of cervical length from 86 women with triplets was analyzed and compared with 2826 measurements of cervical length from 441 women with twins. The rate of cervical shortening among triplet pregnancies was higher than among twin pregnancies starting from 18 weeks of gestation (slope of regression line, -1.297 vs -0.907; P < .001). Similarly, the proportion of women with cervical length of <25 mm or 15 mm was higher among triplet pregnancies than among twin pregnancies (34.0% vs 21.0% [P < .001] and 16.7% vs 8.4% [P = .001]), respectively. For any given cervical length measured after 22 weeks of gestation, the associated gestational length at birth in triplet pregnancies was lower by 2.7 weeks on average compared with twin pregnancies (P < .001).

CONCLUSION

The higher rate of preterm birth in triplet pregnancies, compared with twin pregnancies, is reflected by both a more rapid cervical shortening during gestation and a lower gestational age at birth per any given cervical length.

Prediction of the risk of cesarean delivery after labor induction in twin gestations based on clinical and ultrasound parameters

AIMS

To develop a model based on clinical and ultrasound parameters to predict the risk of cesarean delivery after labor induction in near-term twin gestations.

METHODS

This retrospective cohort study included 189 consecutive women with twin gestations at ≥ 36.0 weeks scheduled for labor induction. The Bishop score and transvaginal ultrasonographic measurements of cervical length were obtained immediately before labor induction. Parameters studied included maternal age, height, weight, parity, gestational age, Bishop score, cervical length, epidural analgesia, method of conception, chorionicity and birth weight. Prostaglandin E2 (dinoprostone) and oxytocin were used for labor induction. Logistic regression analysis and receiver operating characteristic curve were used to generate a predictive model for cesarean delivery.

RESULTS

Fifty (26.5%) of the 189 women had cesarean deliveries. According to logistic regression analysis, maternal height (P = 0.004), parity (P = 0.005) and cervical length (P = 0.016), but not Bishop score (P = 0.920), were identified as independent predictors of cesarean delivery. A risk score based on a model of these three parameters was calculated for each patient. The model was shown to have an adequate goodness of fit (P = 0.201) and the area under the curve was 0.722, indicating fairly good discrimination.

CONCLUSIONS

Maternal height, parity and cervical length were independent parameters for predicting the risk of cesarean delivery after labor induction in twin gestations. A predictive model using these parameters may provide useful information for deciding whether or not to induce labor.

Spontaneous Preterm Birth in Multiples

The number of multiple gestations has increased over the last several decades and preterm birth is one of the leading causes of perinatal morbidity and mortality for these pregnancies. While screening and treatment strategies have achieved moderate success in singleton gestations, screening strategies are less effective in multiple gestations. In addition, to date no intervention aimed at preventing preterm birth has been conclusively shown to either prolong gestation or improve neonatal outcomes for multiple gestations. As in singleton gestations, cervical length is one of the strongest predictors of preterm birth. While not conclusive, emerging data suggest that vaginal progesterone or cervical pessary may be able to prevent preterm birth in twin gestations with a short cervix.

Density of Stromal Cells and Macrophages Associated With Collagen Remodeling in the Human Cervix in Preterm and Term Birth

Remodeling of the cervix occurs in advance of labor both at term and at preterm birth. Morphological characteristics associated with remodeling in rodents were assessed in cervix biopsies from women at term (39 weeks' gestation) and preterm (<33 weeks' gestation). Collagen I and III messenger RNA and hydroxyproline concentrations declined in cervix biopsies from women in labor at term and preterm compared to that in the cervix from nonlaboring women. Extracellular collagen was more degraded in sections of cervix from women at term, based on optical density of picrosirius red stain, versus that in biopsies from nonpregnant women. However, collagen structure was unchanged in the cervix from women at preterm labor versus the nonpregnant group. As an indication of inflammation, cell nuclei density was decreased in cervix biopsies from pregnant women irrespective of labor compared to the nonpregnant group. Moreover, CD68-stained macrophages increased to an equivalent extent in cervix subepithelium and stroma from groups in labor, both at term and preterm, as well as in women not in labor at term. Evidence for a similar inflammatory process in the remodeled cervix of women at term and preterm birth parallels results in rodent models. Thus, a conserved final common mechanism involving macrophages and inflammation may characterize the transition to a ripe cervix before birth at term and in advance of premature birth.

Prediction of impending preterm delivery based on sonographic cervical length and different cytokine levels in cervicovaginal fluid in preterm labor

AIMS

The aim of this study was to determine whether cervicovaginal interleukin (IL)-1β, IL-6 and IL-8 levels, and cervical length, alone or in combination, could predict impending preterm delivery in women with preterm labor and intact membranes.

MATERIAL AND METHODS

Cervicovaginal swab samples for IL-1β, IL-6, and IL-8 assays were taken from 136 consecutive women with preterm labor (23-34 weeks) before the transvaginal ultrasonography examination to measure cervical length. The primary outcome measurement was spontaneous preterm delivery within 7 days of sampling.

RESULTS

Spontaneous preterm delivery within 7 days occurred in 28.6% (39/136) of patients. Receiver-operator characteristic (ROC) curves indicated that cervical length (P < 0.001), cervicovaginal IL-6 (P < 0.001) and IL-8 (P = 0.014), but not IL-1β, could predict delivery within 7 days. According to the logistic regression analysis, high cervicovaginal IL-8 (P = 0.008) and IL-6 (P = 0.038) levels and short cervical length (P < 0.001) were significantly associated with delivery within 7 days, even after controlling for baseline variables. A combination of cervix length and cervicovaginal IL-8 increased the specificity of detecting delivery within 7 days to 92.8%, which was superior to either test alone (P < 0.001), but the sensitivity was only 56.4%.

CONCLUSION

In women with preterm labor, among the parameters assessed, cervicovaginal IL-6 and IL-8 and cervical length are the most important parameters in predicting impending preterm delivery. A combination of cervix length and cervicovaginal IL-8 appeared to be the best for predicting impending preterm delivery, but the relatively low sensitivity of this test may limit its clinical usefulness.

How the cervix shortens: an anatomic study using 3-dimensional transperineal sonography and image registration in singletons and twins

OBJECTIVES

The purpose of this study was to use a fixed reference to study movement (displacement) of the cervical internal os from the second to the third trimester in singletons and twins. The rationale was to gain insight into anatomic changes associated with cervical shortening.

METHODS

For each patient, 2 transperineal scans were performed 12 weeks apart (20 and 32 weeks). The internal os and symphysis pubis were visualized in the same field of view. Image registration techniques were used to align the 2 scans using the symphysis as a fixed reference. Total displacement, anterior displacement, and inferior displacement of the internal os were measured. Displacements were correlated with cervical shortening. Bland-Altman plots and interobserver intraclass correlation coefficients were calculated.

RESULTS

A total of 42 healthy participants were studied: 28 with singletons and 14 with twins. The mean ± SD values for total displacement were 2.1 ± 1.2 and 2.0 ± 1.2 cm for singletons and twins, respectively (P = .75). The direction of displacement was significantly different. The mean anterior displacement was 1.1 cm greater for singletons than for twins (95% confidence interval, 0.29-2.0 cm, P = .01). Mean inferior displacement was 1.3 cm greater for twins than for singletons (95% confidence interval, 2.2-0.1 cm; P = .03). Only inferior displacement correlated with cervical shortening (P < .001; R(2) = 0.74). For every 2.2 cm of inferior displacement, the cervix shortened 1.0 cm. Assessments of reliability showed good agreement between 2 observers.

CONCLUSIONS

The anatomic position of the internal cervical os depends on gestational age and fetal number. Cervical shortening correlated most strongly with inferior displacement.

Two-stage transvaginal cervical length screening for preterm birth in twin pregnancies

AIM

To compare cervical length (CL) at 18-21 and 22-25 weeks' gestation in twin pregnancies in prediction of spontaneous preterm delivery and to examine cervical shortening.

METHODS

Retrospective cohort study of CL measured at 18-21 and 22-25 weeks' gestation in twin pregnancies.

RESULTS

Receiver operating characteristics (ROC) curve revealed area of 0.64 (95% CI 0.53-0.75) and 0.80 (95% CI 0.72-0.88) for measurements at 18-21 and 22-25 weeks, respectively (P<or=0.001). Sensitivities of 33.3% and 23% and negative predicting value (NPV) of 97.3% and 86.8% for delivery at <28 and <34 weeks gestation were reached for measurements at 18-21 weeks. Sensitivities of 71.4% and 38.2% and NPV of 99.1% and 91.4% for delivery at <28 and <34 weeks' gestation were reached for measurements at 22-25 weeks. Cervical length shortening analysis showed an area under ROC curve of 0.81 (95% CI 0.73-0.89) and best cut-off was at >or=2 mm/week. Sensitivities of 80% and 60.8% and NPV of 98.9% and 90.6% for delivery at <28 and <34 weeks gestation were reached.

CONCLUSIONS

In twin gestations, assessment of CL at 22-25 weeks is better than assessment at 18-21 weeks to predict preterm delivery before 34 weeks. Cervical shortening at a rate of >or=2 mm/weeks between 18 and 25 weeks gestation was a good predictor of spontaneous preterm birth in this high-risk population.

Body mass index, Bishop score, and sonographic measurement of the cervical length as predictors of successful labor induction in twin gestations

AIMS

To evaluate the predictive value of body mass index (BMI), Bishop score, and sonographic measurement of cervical length for predicting successful labor induction (defined as an ability to achieve the active phase of labor corresponding to a cervical dilatation of > or =4 cm within 12 h of initiating oxytocin) in near-term twin gestations.

METHODS

This prospective, observational study enrolled 72 consecutive women with twin gestations at >36.0 weeks' gestation who were scheduled for induction of labor. Transvaginal ultrasound for measurement of the cervical length was performed and the Bishop score was determined by digital examination. The BMI was calculated based on the weight and height at the time of induction.

RESULTS

Labor induction was successful in 63% (45/72) of women. The mean BMI was significantly lower in women who had successfully induced labor, but no significant differences existed with respect to the mean cervical length, median Bishop score, proportion of parous and nulliparous women, and the mean total birth weight of the twin pairs between the two patient groups. Multiple logistic regression demonstrated that only BMI provided a significant contribution in predicting successful labor induction.

CONCLUSIONS

BMI independently predicted the success of labor induction in twin gestations but the sonographic measurement of the cervical length and Bishop score had poor predictive values for successful induction.

A method to visualize 3-dimensional anatomic changes in the cervix during pregnancy: a preliminary observational study

OBJECTIVE

The purpose of this study was to develop a method to visualize 3-dimensional (3D) anatomic changes in the cervix and lower uterine segment during the antepartum period.

METHODS

An observational study of patients with both uncomplicated and complicated pregnancies was performed. To visualize 3D anatomic changes, solid models were constructed from 3D sonographic data. Model construction followed a 3-step protocol. First, 3D transvaginal sonographic data of the cervix and lower uterine segment were obtained. Second, sonographic data were exported to a medical image-processing program, which was used to align 3D sonographic data obtained from a single patient at different time points. Last, sonographic data were used to guide construction of solid models using mechanical design software. Anatomic changes were visualized by comparing solid models constructed from sonographic data obtained at different time points.

RESULTS

From 16 patients who consented, 5 patients were selected for this study. Two to 4 models were derived from each of the 5 patients at 15 to 38 weeks' gestation. To show anatomic changes in the cervix and lower uterine segment, solid models from different time points in the same patient were superimposed. A total of 16 solid models were constructed. In addition, 3D changes associated with second-trimester cervical failure and successful therapeutic cerclage were shown.

CONCLUSIONS

A method to visualize 3D cervical changes is presented, revealing complex anatomic changes in the lower uterine segment, cervical stroma, and cervical mucosa as pregnancy progresses.

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.

Using Generalized Estimating Equations to Analyze Longitudinal Data in Nursing Research

Although use of GEE has become widespread for analyzing longitudinal data in many fields, much research in nursing still uses only the traditional statistical methods. This article illustrates use of GEE, using a data set describing symptoms of women with gynecological cancers, with eight data collection times across a period of 6 months. Three research questions are analyzed: (a) Did number of symptoms in women with gynecological cancer change within 6 months after surgery? (b) Did individual symptom (e.g., pain) in women with gynecological cancers change within 6 months after surgery? (c) Were psychosocial and disease variables (age, cancer site, new diagnosis or recurrence, treatment, emotional distress, and use of symptom management toolkit) associated with individual symptoms (e.g., fatigue) in women with gynecological cancers? For each research question, SAS code and explanation of SAS instructions are described in detail. Missing data and time intervals for longitudinal studies are also discussed.

The effect of polyhydramnios on cervical length in twins: a controlled intervention study in complicated monochorionic pregnancies

Objective

To test the hypothesis that cervical shortening in polyhydramnios reflects the degree of excess amniotic fluid, and increases with normalisation of amniotic fluid volume.

Study Design

Prospective cohort study of 40 women with monochorionic twins undergoing interventional procedures between 16–26 weeks. Cervical length was assessed via transvaginal sonography pre-procedure, 1 and 24 hours post-procedure, and results compared between amnioreduction and control procedures. Amniotic fluid index (AFI) was measured pre- and post-procedure.

Results

Pre-procedural cervical length correlated with AFI (linear fit = 5.07 -0.04x, R² = 0.17, P = 0.03) in patients with polyhydramnios (n = 28). Drainage of 2000ml fluid (range 700–3500ml), reduced AFI from 42cm to 21cm (P<0.001). Their pre-procedural cervical length did not change at one (mean Δ:−0.1cm, 95%CI, −0.4 to 0.2) or 24 hours (0.2cm, −0.1 to 0.6) after amnioreduction. There was no change in cervical length at control procedures.

Conclusion

Cervical shortening in twins with polyhydramnios does not appear to be an acute process; cervical length can be measured before or after therapeutic procedures.