Impaired ultrasonographic cervical assessment after voiding: a randomized controlled trial

Contractions of the lower uterine segment during transvaginal ultrasound cervical length: incidence, significance, proper measurement, and management

An accurate transvaginal ultrasound cervical length is paramount to obtain the best prediction for preterm birth. Transvaginal ultrasound cervical length should be optimally obtained when a lower uterine segment contraction is not seen. For universal transvaginal ultrasound cervical length screening at approximately 20 weeks of gestation, the options are to do the transvaginal ultrasound soon after bladder void (lower uterine segment contractions present in 16%-43% of this approach) or to wait until the end of the anatomy scan (ideally within 30 minutes after bladder voiding) to decrease the chance of a lower uterine segment contraction. If the lower uterine segment contraction persists even after waiting up to 20 minutes or more, only the true transvaginal ultrasound cervical length should be reported. In particular, in patients with a previous spontaneous preterm birth, if the lower uterine segment contraction persists, the transvaginal ultrasound cervical length can be repeated in ≤7 days even in the presence of a normal (>25 mm) cervical length. Similar to a blood pressure cuff that must be of the right size for proper blood pressure measurement and a glucometer that must be properly calibrated, screening with transvaginal ultrasound cervical length should only be performed following a proper and standardized technique, including avoiding as much as feasible the presence of lower uterine segment contractions.

Real-time ultrasound demonstration of uterine isthmus contractions during pregnancy

BACKGROUND

Asymptomatic isthmic contractions are a frequent physiological phenomenon in pregnancy, sometimes triggered by bladder voiding. They can interfere with proper cervical length assessment and may lead to false images of placenta previa. However, there is limited research on the prevalence and characteristics of these contractions.

OBJECTIVE

This study aimed to determine the prevalence and characteristics of isthmic contractions after bladder voiding in the second trimester of pregnancy, to evaluate their effect on cervical length assessment, and to propose a new method for the objective assessment of the presence and intensity of isthmic contractions.

STUDY DESIGN

In this prospective observational study, long videos of the uterine cervix were recorded in 30 singleton pregnancies during the second trimester of pregnancy after bladder voiding. Isthmic length and cervicoisthmic length changes were assessed over time. The isthmic length was measured using a new approach, which involved calculating the distance from the base of the cervix to the internal os, including the isthmus.

RESULTS

Isthmic contractions were observed in 43% of pregnant women (95% confidence interval, 26%-62%) after bladder voiding. The median time for complete isthmus relaxation was 19.7 minutes (95% confidence interval, 15.0 to not available). No substantial differences in maternal characteristics were found between individuals with and without contractions. The proposed method for measuring isthmic length provided an objective assessment of the presence and intensity of isthmic contractions. A cutoff of 18 mm in isthmic length allowed for the distinction of pregnant women presenting a contraction. In addition, the study identified a characteristic undulatory pattern in the relaxation of the isthmus in half of the cases with contractions.

CONCLUSION

Isthmic contractions are a common occurrence after bladder voiding in the second trimester of pregnancy and may interfere with proper cervical length assessment. We recommend performing cervical assessment at least 20 minutes after bladder voiding to reduce the risk of bias in cervical length measurement and to avoid false images of placenta previa. The new method for measuring isthmic length provides an objective way to assess the presence and intensity of isthmic contractions. Further research is needed to understand the role of isthmic contractions in the physiology of pregnancy and birth.

The overlooked impact of lower uterine segment contractions on second trimester cervical assessment

INTRODUCTION

Asymptomatic contractions in the lower uterine segment (LUS) may affect uterocervical angle and cervical length; however, this has never been investigated. Therefore, the aim of this study was to evaluate the effect of LUS contractions on uterocervical angle, cervical length and LUS thickness.

MATERIALS AND METHODS

This was a prospective, observational, single-cohort study conducted on 102 asymptomatic singleton pregnancies between 19.0 and 22.6 weeks of gestation. Uterocervical angle and cervical length were measured by transvaginal ultrasound at two different time points with an interval of at least 20 minutes. LUS thickness was also measured as an indirect marker of myometrial contraction. A linear and curvilinear regression were performed to explore a potential association between LUS contractions, measured as increments in LUS thickness, and changes in cervical length and uterocervical angle.

RESULTS

The linear regression between changes in LUS thickness and changes in cervical length showed that LUS contractions impact CL; for every one-millimeter increase in LUS thickness, cervical length increased by 0.909 mm, when the isthmus was included in the cervical length measurement (R2=0.358; β=0.909; P<0.001). By contrast, when the isthmus was not included in the measurement, a curvilinear relation between changes in LUS thickness and changes in cervical length was found (R2=0.077; β1=0.575, β2=0.038; P=0.018). The relation between changes in uterocervical angle and changes in LUS thickness was not significant.

DISCUSSION/CONCLUSION

LUS contractions can be observed in many asymptomatic women during the second trimester of pregnancy. LUS contractions lead to an increase in cervical length and LUS thickness, thus impacting ultrasound cervical assessments. These contractions do not affect the uterocervical angle.

Mid-Trimester Cervical Length Screening: Effect of Poorly Developed Lower Uterine Segment on Pregnancy Outcome

OBJECTIVES

To identify whether a poorly developed lower uterine segment (PDLUS) observed during cervical length (CL) screening affects the duration of gestation in women with no prior spontaneous preterm birth (sPTB).

MATERIALS AND METHODS

A retrospective cohort study of women with a singleton gestation and no prior sPTB, who underwent transvaginal CL screening at our institution. We excluded women with progesterone exposure, major anomalies, and women delivering elsewhere. Women with PDLUS were compared to those with a measured (normal) CL ≥25 mm.

PRIMARY OUTCOME

birth gestational age (GA).

SECONDARY OUTCOMES

sPTB <35 and 37 weeks, hospital evaluation for preterm labor without delivery, delivery indication, and mode. A Cox proportional-hazards survival model considered time from CL scan to delivery. We powered the study to detect a one-half week difference in birth GA.

RESULTS

We included 270 women with PDLUS and 985 women with normal CL. Mean birth GA was 38.9 ± 2.0 weeks with PDLUS versus 38.7 ± 2.4 weeks with normal CL (p = .10). Women with PDLUS were less likely to experience sPTB <37 weeks (1.1% vs 3.6%; p = 0.04). There was no difference in sPTB <35 weeks (0.8% vs 1.7%; p = .25). Hospital evaluation for preterm labor (17% vs 19%; p = .54), delivery indication, and mode were not different. The hazard ratio for earlier birth in women with PDLUS was 0.67 (95% CI 0.46, 0.98; p = .04).

CONCLUSIONS

We observed no difference in mean GA at birth; however, PDLUS was protective against sPTB <37 weeks and was associated with a lower hazard ratio for earlier birth.

Universal transvaginal cervical length screening during pregnancy increases the diagnostic incidence of low-lying placenta and placenta previa

BACKGROUND

Universal transvaginal cervical length screening has been increasingly implemented with both positive and negative consequences.

OBJECTIVE

In this study, we described the diagnostic incidence of low-lying placenta and placenta previa with the implementation of universal transvaginal cervical length screening.

STUDY DESIGN

This is a retrospective cohort study of women undergoing midtrimester universal transvaginal cervical length screening. The primary outcome was the rate of transvaginal diagnosis of low-lying placenta or placenta previa using midtrimester universal transvaginal cervical length screening.

RESULTS

This study included 1982 midtrimester ultrasounds, of which 211 indicated a low-lying placenta or placenta previa on either transabdominal or transvaginal ultrasound. With transvaginal ultrasound, a low-lying placenta or placenta previa was diagnosed in 211 women (10.6% of the study population). Of the 211 patients with a low-lying placenta or placenta previa, 90 (42.6%) had a false-negative result, diagnosed using only transvaginal ultrasound; 112 (53.1%) had a true-positive result; and 9 (4.3%) had a false-positive result. The relative risk of having an abnormal finding on ultrasound with the addition of universal transvaginal cervical length screening was 9.2 (95% confidence interval, 4.6-18.1). Of the low-lying placenta or placenta previa diagnosed using midtrimester universal transvaginal cervical length screening, 98.9% resolved (95% confidence interval, 93.7-99.97).

CONCLUSION

Implementation of universal transvaginal cervical length screening increases the diagnostic incidence of low-lying placenta or placenta previa without an increase in the diagnoses that persist to term, which comes at the cost of increased follow-up ultrasounds and potentially increased anxiety for the patient.

Cervical assessment by ultrasound for preventing preterm delivery

BACKGROUND

Measurement of cervical length by ultrasound is predictive of preterm birth (PTB). There are three methods of ultrasound cervical assessment: transvaginal (TVU), transabdominal (TAU), and transperineal (TPU, also called translabial). Cervical length measured by TVU is a relatively new screening test, and has been associated with better prediction of PTB than previously available tests. It is unclear if cervical length measured by ultrasound is effective for preventing PTB. This is an update of a review last published in 2013.

OBJECTIVES

To assess the effectiveness of antenatal management based on transvaginal, transabdominal, and transperineal (also called translabial) ultrasound screening of cervical length for preventing preterm birth.

SEARCH METHODS

For this update, we searched the Cochrane Pregnancy and Childbirth's Trials Register, ClinicalTrials.gov, and the WHO International Clinical Trials Registry Platform (ICTRP) to 30 August 2018; reviewed the reference lists of all articles, and contacted experts in the field for additional and ongoing trials.

SELECTION CRITERIA

We included published and unpublished randomised controlled trials (RCT) including pregnant women between the gestational ages of 14 to 32 weeks, for whom the cervical length was screened for risk of PTB with TVU, TAU, or TPU. This review focused on studies based on knowledge versus no knowledge of cervical length results, or ultrasound versus no ultrasound for cervical length. We excluded studies based on interventions (e.g. progesterone, cerclage) for short cervical length.

DATA COLLECTION AND ANALYSIS

We followed standard Cochrane methods.

MAIN RESULTS

We included seven RCTs (N = 923): one examined asymptomatic women with twin pregnancies; four included women with singleton pregnancies and symptoms of preterm labour (PTL); one included women with singleton pregnancies and symptoms of preterm premature rupture of membranes (PPROM); and one included asymptomatic singletons. All trials used TVU for screening.We assessed the risk of bias of the included studies as mixed, and the quality of the evidence for primary outcomes as very low for all populations.For asymptomatic women with twin pregnancies, it is uncertain whether knowledge of TVU-measured cervical length compared to no knowledge reduces PTB at less than 34 weeks (risk ratio (RR) 0.62, 95% confidence intervals (CI) 0.30 to 1.25; 1 study, 125 participants) because the quality of the evidence is very low. The results were also inconclusive for preterm birth at 36, 32, or 30 weeks; gestational age at birth, and other maternal and perinatal outcomes.Four trials examined knowledge of TVU-measured cervical length of singletons with symptoms of PTL versus no knowledge. We are uncertain of the effects because of inconclusive results and very low-quality evidence for: preterm births at less than 37 weeks (average RR 0.59, 95% CI 0.26 to 1.32; 2 studies, 242 participants; I² = 66%; Tau² = 0.23). Birth occurred about four days later in the knowledge groups (mean difference (MD) 0.64 weeks, 95% CI 0.03 to 1.25; 3 trials, 290 women). The results were inconclusive for the other outcomes for which there were available data: PTB at less than 34 or 28 weeks; birthweight less than 2500 g; perinatal death; maternal hospitalisation; tocolysis; and steroids for fetal lung maturity.The trial of singletons with PPROM (N = 92) evaluated safety of using TVU to measure cervical length in this population as its primary outcome, not its effect on management. The results were inconclusive for incidence of maternal and neonatal infections between the TVU and no ultrasound groups.In the trial of asymptomatic singletons (N = 296), in which women either received TVU or not, the results were inconclusive for preterm birth at less than 37 weeks (RR 1.27, 95% CI 0.61 to 2.61; I² = 0%), gestational age at birth, and other perinatal and maternal outcomes.We downgraded evidence for limitations in study design, inconsistency between the trials, and imprecision, due to small sample size and wide confidence intervals crossing the line of no effect.No trial compared the effect of knowledge of the CL with no knowledge of CL in other populations, such as asymptomatic women with singleton pregnancies, or symptomatic women with twin pregnancies.

AUTHORS' CONCLUSIONS

There are limited data on the effects of knowing the cervical length, measured by ultrasound, for preventing preterm births, which preclude us from drawing any conclusions for women with asymptomatic twin or singleton pregnancies, singleton pregnancies with PPROM, or other populations and clinical scenarios.Limited evidence suggests that knowledge of transvaginal ultrasound-measured cervical length, used to inform the management of women with singleton pregnancies and symptoms of preterm labour, appears to prolong pregnancy by about four days over women in the no knowledge groups.Future studies could look at specific populations separately (e.g. singleton versus twins; symptoms versus no symptoms of PTL), report on all pertinent maternal and perinatal outcomes, and include cost-effectiveness analyses. Most importantly, future studies should include a clear protocol for management of women based on TVU-measured cervical length.

Intraobserver variability in fibroid size measurements: estimated effects on assessing fibroid growth

OBJECTIVES

To evaluate intraobserver variability of fibroid sonographic measurements and apply this factor to fibroid growth assessment.

METHODS

Study participants were African American women aged 23 to 34 years who had never had a diagnosis of uterine fibroids. All participants underwent transvaginal sonography to screen for the presence of previously undiagnosed fibroids (≥0.5 cm in diameter). The diameters of up to 6 fibroids were measured in 3 perpendicular planes at 3 separate times during the examinations by experienced sonographers. Intraobserver variability as measured by the coefficient of variation (CV) for fibroid diameter and volume was calculated for each fibroid, and factors associated with the CV were assessed by regression models. The impact of variability on growth assessment was determined.

RESULTS

Ninety-six of 300 women screened were found to have at least 1 fibroid, yielding a total of 174 fibroids for this analysis. The mean CV for the 3 measurements of fibroid maximum diameter was 5.9%. The mean CV for fibroid volume was 12.7%. Fibroid size contributed significantly to intraobserver variability (P = .04), with greater variability for smaller fibroids. Fibroid type (submucosal, intramural, or subserosal) was not important. Fibroids from the same woman tended to have similar measurement variability when assessed for volume but not for maximum diameter. Calculations showed that when following up fibroids, as much as a 20% increase in diameter could be due to measurement error, not "true growth."

CONCLUSIONS

A small fibroid must have a greater change in size than a large fibroid to conclude that it is growing, but even for small fibroids an increase in diameter of greater than 20% is likely to indicate true growth, not measurement variability.