Ultrasound safety in early pregnancy: reduced energy setting does not compromise obstetric Doppler measurements

Evaluation fetal heart in the first and second trimester: Results and limitations

Background

Cardiac heart defects affect nearly 6-12 per 1000 live births in the general population and are more frequent than common trisomies.

Aim

To assess the efficacy and technical limitations of first-trimester fetal heart evaluation in the 11-14^th-weeks' scan and comparison with the second-trimester anatomical exam by ultrasound.

Material and Method

Between April 2015 and July 2020, medical records and ultrasound data of 3295 pregnancies who underwent first-trimester fetal anatomy exams by ultrasound were reviewed retrospectively. All ultrasound exams were performed by the same two operators (TUKD, OP) with transabdominal transducers. Fetal situs, four-chamber view, outflow tracts, and three-vessel trachea view are the cornerstones of first-trimester fetal heart examination. Conventional grayscale mode and high-definition power Doppler mode were utilized. The same operators re-examined all cases between the 18 and 23 weeks of gestation by ISUOG guidelines.

Results

We performed a combined transvaginal and transabdominal approach for only 101 cases (3.06%). The mean maternal age was 31.28 ± 4.43, the median gestational age at the first-trimester ultrasound exam was 12.4 weeks, and the median CRL was 61.87 mm (range was 45.1-84 mm). Even combined approach situs, cardiac axis, and four-chamber view could not be visualized optimally in 28 cases (0.7%). Outflow tracts were visualized separately in 80% (2636 in 3295) cases. Three vessel-trachea views were obtained in 85.4% (2814 in 3295) cases by high-definition Doppler mode. There were 47 fetuses with cardiac defects in 3295 pregnancies with the known pregnancy outcome. Ten cases had abnormal karyotype results. Thirty-two fetuses with cardiac anomalies (9.7 in 1000 pregnancies) were detected in the first-trimester examination, and the remaining 15 (4.55 in 1000 pregnancies) cases were diagnosed in the second-trimester examination. The prevalence of congenital cardiac anomalies was 14.25 in 1000 pregnancies. Fifteen cases were missed in the first-trimester exam. Also, ten fetuses which had abnormal cardiac findings in the first-trimester exam were not confirmed in the second-trimester exam. Sensitivity, specificity, positive, and negative predictive values were calculated as 65.3%, 99.7%, 66.8%, and 99.67%, respectively.

Conclusion

Late first-trimester examination of the fetus is feasible and allows earlier detection of many structural abnormalities of the fetus, including congenital heart defects. Suspicious and isolated cardiac abnormal findings should be re-examined and confirmed in the second-trimester exam. Previous abdominal surgery, high BMI, and subtle cardiac defects can cause missed cardiac abnormalities.

Comparison of fetal and maternal tissue elasticity between euploid and aneuploid pregnancies by shear wave elastography

AIM

B-mode ultrasonography utilized for fetal screening of common trisomies is referred to as a genetic sonogram and includes determining major abnormalities and soft markers such as hypoplastic nasal bone and increased thickness of the nuchal fold. Elastography is a novel ultrasound technique giving information about tissue stiffness used for diagnosing cancer, transplant rejection, and organ fibrosis. This study aimed to determine via shear wave elastography (SWE) whether euploid and aneuploid fetal soft marker tissues vary in stiffness.

METHODS

The participants were all singleton pregnancies between 19 and 23 weeks of gestation; 35 euploid and 14 aneuploid fetus pregnancies were enrolled. Fetal bowel, kidney, liver, nasal bone, nuchal fold, placenta, and myometrium were investigated with SWE using acoustic radiation impulse force. Images were analyzed with a novel software calibrated and written by us using MATLAB. Statistical analysis was completed with the SPSS Program. Shapiro-Wilk normality distribution analysis, Student's t-test, and Mann-Whitney U methods were used.

RESULTS

The mean shear wave speed of fetal nasal bone was significantly lower in aneuploid fetuses. There was no difference between other tissues in mean shear wave velocity.

CONCLUSIONS

Euploid and aneuploid fetuses have different elastic properties of the nasal bone and this may have a role in differentiating aneuploid fetuses noninvasively.

First-trimester ultrasound detection of fetal heart anomalies: systematic review and meta-analysis

OBJECTIVES

To determine the diagnostic accuracy of ultrasound at 11-14 weeks' gestation in the detection of fetal cardiac abnormalities and to evaluate factors that impact the detection rate.

METHODS

This was a systematic review of studies evaluating the diagnostic accuracy of ultrasound in the detection of fetal cardiac anomalies at 11-14 weeks' gestation, performed by two independent reviewers. An electronic search of four databases (MEDLINE, EMBASE, Web of Science Core Collection and The Cochrane Library) was conducted for studies published between January 1998 and July 2020. Prospective and retrospective studies evaluating pregnancies at any prior level of risk and in any healthcare setting were eligible for inclusion. The reference standard used was the detection of a cardiac abnormality on postnatal or postmortem examination. Data were extracted from the included studies to populate 2 × 2 tables. Meta-analysis was performed using a random-effects model in order to determine the performance of first-trimester ultrasound in the detection of major cardiac abnormalities overall and of individual types of cardiac abnormality. Data were analyzed separately for high-risk and non-high-risk populations. Preplanned secondary analyses were conducted in order to assess factors that may impact screening performance, including the imaging protocol used for cardiac assessment (including the use of color-flow Doppler), ultrasound modality, year of publication and the index of sonographer suspicion at the time of the scan. Risk of bias and quality assessment were undertaken for all included studies using the Quality Assessment of Diagnostic Accuracy Studies (QUADAS-2) tool.

RESULTS

The electronic search yielded 4108 citations. Following review of titles and abstracts, 223 publications underwent full-text review, of which 63 studies, reporting on 328 262 fetuses, were selected for inclusion in the meta-analysis. In the non-high-risk population (45 studies, 306 872 fetuses), 1445 major cardiac anomalies were identified (prevalence, 0.41% (95% CI, 0.39-0.43%)). Of these, 767 were detected on first-trimester ultrasound examination of the heart and 678 were not detected. First-trimester ultrasound had a pooled sensitivity of 55.80% (95% CI, 45.87-65.50%), specificity of 99.98% (95% CI, 99.97-99.99%) and positive predictive value of 94.85% (95% CI, 91.63-97.32%) in the non-high-risk population. The cases diagnosed in the first trimester represented 63.67% (95% CI, 54.35-72.49%) of all antenatally diagnosed major cardiac abnormalities in the non-high-risk population. In the high-risk population (18 studies, 21 390 fetuses), 480 major cardiac anomalies were identified (prevalence, 1.36% (95% CI, 1.20-1.52%)). Of these, 338 were detected on first-trimester ultrasound examination and 142 were not detected. First-trimester ultrasound had a pooled sensitivity of 67.74% (95% CI, 55.25-79.06%), specificity of 99.75% (95% CI, 99.47-99.92%) and positive predictive value of 94.22% (95% CI, 90.22-97.22%) in the high-risk population. The cases diagnosed in the first trimester represented 79.86% (95% CI, 69.89-88.25%) of all antenatally diagnosed major cardiac abnormalities in the high-risk population. The imaging protocol used for examination was found to have an important impact on screening performance in both populations (P < 0.0001), with a significantly higher detection rate observed in studies using at least one outflow-tract view or color-flow Doppler imaging (both P < 0.0001). Different types of cardiac anomaly were not equally amenable to detection on first-trimester ultrasound.

CONCLUSIONS

First-trimester ultrasound examination of the fetal heart allows identification of over half of fetuses affected by major cardiac pathology. Future first-trimester screening programs should follow structured anatomical assessment protocols and consider the introduction of outflow-tract views and color-flow Doppler imaging, as this would improve detection rates of fetal cardiac pathology. © 2021 The Authors. Ultrasound in Obstetrics & Gynecology published by John Wiley & Sons Ltd on behalf of International Society of Ultrasound in Obstetrics and Gynecology.

Safety Aspects of Perinatal Ultrasound

Ultrasound safety is of particular importance in fetal and neonatal scanning. Fetal tissues are vulnerable and often still developing, the scanning depth may be low, and potential biological effects have been insufficiently investigated. On the other hand, the clinical benefit may be considerable. The perinatal period is probably less vulnerable than the first and second trimesters of pregnancy, and ultrasound is often a safer alternative to other diagnostic imaging modalities. Here we present step-by-step procedures for obtaining clinically relevant images while maintaining ultrasound safety. We briefly discuss the current status of the field of ultrasound safety, with special attention to the safety of novel modalities, safety considerations when ultrasound is employed for research and education, and ultrasound of particularly vulnerable tissues, such as the neonatal lung. This CME is prepared by ECMUS, the safety committee of EFSUMB, with contributions from OB/GYN clinicians with a special interest in ultrasound safety.

In vitro characterisation of ultrasound-induced heating effects in the mother and fetus: A clinical perspective

INTRODUCTION

The quantification of heating effects during exposure to ultrasound is usually based on laboratory experiments in water and is assessed using extrapolated parameters such as the thermal index. In our study, we have measured the temperature increase directly in a simulator of the maternal-fetal environment, the 'ISUOG Phantom', using clinically relevant ultrasound scanners, transducers and exposure conditions.

METHODS

The study was carried out using an instrumented phantom designed to represent the pregnant maternal abdomen and which enabled temperature recordings at positions in tissue mimics which represented the skin surface, sub-surface, amniotic fluid and fetal bone interface. We tested four different transducers on a commercial diagnostic scanner. The effects of scan duration, presence of a circulating fluid, pre-set and power were recorded.

RESULTS

The highest temperature increase was always at the transducer-skin interface, where temperature increases between 1.4°C and 9.5°C were observed; lower temperature rises, between 0.1°C and 1.0°C, were observed deeper in tissue and at the bone interface. Doppler modes generated the highest temperature increases. Most of the heating occurred in the first 3 minutes of exposure, with the presence of a circulating fluid having a limited effect. The power setting affected the maximum temperature increase proportionally, with peak temperature increasing from 4.3°C to 6.7°C when power was increased from 63% to 100%.

CONCLUSIONS

Although this phantom provides a crude mimic of the in vivo conditions, the overall results showed good repeatability and agreement with previously published experiments. All studies showed that the temperature rises observed fell within the recommendations of international regulatory bodies. However, it is important that the operator should be aware of factors affecting the temperature increase.

EFSUMB Clinical Safety Statement for Diagnostic Ultrasound - (2019 revision)

This document is the updated 2019 revision of the EFSUMB Clinically Safety Statement. A Safety Statement has been published by EFSUMB annually since 1994 by the Safety Committee (ECMUS) of the federation. The text is deliberately brief and gives a concise overview of safety in the use of diagnostic ultrasound.

Do current Philips ultrasound systems exceed the recommended safety limits during routine prenatal ultrasounds?

Background

Biological safety of ultrasound is a complex and nuanced subject that is poorly understood by ultrasound users. Little is known about the acoustic output and thermal index levels during the routine use of modern ultrasound machines in prenatal scanning.

Methodology

This study was a retrospective review of thermal index (TI) values encountered during 300 prenatal ultrasound examinations (100 in each trimester) performed on any one of 13 Philips Epiq 7 or Epiq 5 systems, representing approximately 106.5 h of real-time scanning. The TI levels were compared to three international guidelines on the biological safety of ultrasound.

Results

The routine use of current Philips systems was associated with low TI levels. Of the 300 examinations reviewed, virtually all were compliant with the BMUS and Nelson safety guideline. Whether the examination was compliant with the WFUMB guideline is open to interpretation. The highest level of TI encountered was 1.1. In no instance did the TI level incur into the 'not recommended' range or into a range where specific user action was required to reduce the TI within 1 min. The most frequent action associated with TI > 0.7 was the use of M-mode to document the fetal heart rate. In the four instances where TI peaked at 1.1, 3 were associated with the use of M-mode and one with B-mode. Spectral Doppler was not implicated in high TI levels. These results are surprising and open up a range of opportunities for future study.

Measured acoustic intensities for clinical diagnostic ultrasound transducers and correlation with thermal index

OBJECTIVES

To investigate if the thermal index for bone (TIB) displayed on screen is an adequate predictor for the derated spatial-peak temporal-average (I_SPTA.3 ) and spatial-peak pulse-average (I_SPPA.3 ) acoustic intensities in a selection of clinical diagnostic ultrasound machines and transducers.

METHODS

We calibrated five clinical diagnostic ultrasound scanners and 10 transducers, using two-dimensional grayscale, color Doppler and pulsed-wave Doppler, both close to and far from the transducer, with a TIB between 0.1 and 4.0, recording 103 unique measurements. Acoustic measurements were performed in a bespoke three-axis computer-controlled scanning tank, using a 200-μm-diameter calibrated needle hydrophone.

RESULTS

There was significant but poor correlation between the acoustic intensities and the on-screen TIB. At a TIB of 0.1, the I_SPTA.3 range was 0.51-50.49 mW/cm² and the I_SPPA.3 range was 0.01-207.29 W/cm² . At a TIB of 1.1, the I_SPTA.3 range was 19.02-309.44 mW/cm² and the I_SPPA.3 range was 3.87-51.89 W/cm² .

CONCLUSIONS

TIB is a poor predictor for I_SPTA.3 and I_SPPA.3 and for the potential bioeffects of clinical diagnostic ultrasound scanners. Copyright © 2016 ISUOG. Published by John Wiley & Sons Ltd.

Acoustic output measured by thermal and mechanical indices during fetal echocardiography at the time of the first trimester scan

We measured acoustic output, expressed as the thermal index (TI) and mechanical index (MI), during fetal echocardiography at the time of the first trimester scan. TI and MI were retrieved from the saved displays during gray-mode, high-definition color flow Doppler and pulsed-wave Doppler (tricuspid flow) ultrasound examinations of the fetal heart and from the ductus venosus assessment. A total of 399 fetal cardiac examinations were evaluated. There was a significant increase in TI values from B-mode studies (0.07 ± 0.04 [mean ± SD]) to color flow mapping (0.2 ± 0.0) and pulsed-wave Doppler studies (0.36 ± 0.05). The TI from ductus venosus assessment (0.1 ± 0.01) was significantly lower than those from Doppler examinations of the heart. MI values from B-mode scans (0.65 ± 0.12) and color flow mapping (0.71 ± 0.11) were comparable, although different, and both values were higher than those from pulsed-wave Doppler tricuspid evaluation (0.39 ± 0.03). There were no differences in MI values from power Doppler assessment between the tricuspid flow and ductus venosus. Safety indices were remarkably stable and were largely constant, especially for color Doppler (TI), tricuspid flow (MI) and ductus venosus assessment (TI, MI). We acquired satisfactory Doppler images and/or signals at acoustic levels that were lower than the actual recommendations and never reached a TI of 0.5.

Do clinical practitioners seeking credentialing for nuchal translucency measurement demonstrate compliance with biosafety recommendations? Experience of the Nuchal Translucency Quality Review Program

OBJECTIVES

The purpose of this study was to evaluate compliance with the ALARA (as low as reasonably achievable) principle by practitioners seeking credentialing for nuchal translucency (NT) measurement between 11 and 14 weeks' gestation.

METHODS

Nuchal Translucency Quality Review Program credentialing requires quantitative scoring of 5 NT measurements from 5 different fetuses. Images submitted by 100 consecutive practitioners were retrospectively evaluated for the output display standard (ODS). The thermal index (TI) type (bone [TIb] or soft tissue [TIs]) and numeric value of the index were recorded. The TIb was considered the correct index for this study. Compliance with the numeric value was evaluated in several ways. Collectively, a TIb lower than 0.5 was considered optimal, lower than 0.7 compliant, and 1.0 or lower satisfactory.

RESULTS

An ODS was present in at least 1 image submitted by 77 practitioners. The TIb was used exclusively by 15 (19.5%), the TIs by 37 (48.1%), and 25 used a combination of the TIb and TIs. Only 4 of 77 providers (5%) used the correct TI type (TIb) at lower than 0.5 for all submitted images, 5 of 77 (6%) at lower than 0.7, and 9 of 77 (12%) at 1.0 or lower. A TI (TIb or TIs) higher than 1.0 was used by 15 of 77 providers (19.5%). Proficiency in NT measurement and educational background (physician or sonographer) did not influence compliance with ALARA.

CONCLUSIONS

Clinicians seeking credentialing in NT do not demonstrate compliance with the recommended use of the TIb in monitoring acoustic output.

First-trimester detection of major cardiac defects with the use of ductus venosus blood flow

OBJECTIVE

To assess the best method of combining fetal nuchal translucency (NT) and ductus venosus (DV) blood flow measurements in the detection of major cardiac defects in chromosomally normal fetuses during the first-trimester scan.

METHODS

During an 8-year period NT and DV blood flow were routinely assessed at 11-14 weeks' gestation. Only chromosomally normal singleton pregnancies were included in the study. When a cardiac defect was suspected, or when increased fetal NT and/or absent or reversed (AR) A-wave in the DV was observed, early fetal echocardiography was offered. Data on routine second- and third-trimester scans, neonatal follow-up or postmortem examination were obtained from hospital records. The detection and false-positive rates for all major cardiac defects were calculated for several screening strategies, including: NT or DV pulsatility index for veins (DV-PIV) above a fixed normal centile; AR A-wave; risk based on NT and DV-PIV or A-wave velocity above a fixed normal centile; and combinations of these strategies.

RESULTS

The study population included 37 chromosomally normal fetuses with a major cardiac defect and 12 799 unaffected pregnancies. Fetal NT above the 95(th) or the 99(th) centile and AR A-wave was observed in 40, 27 and 39% of the fetuses with major cardiac defects, respectively. A 47% detection rate with a 2.7% false-positive rate was obtained when AR A-wave or NT above the 99(th) centile was used as the selection criterion.

CONCLUSIONS

Half of major fetal cardiac defects could be detected in the first trimester if NT and DV Doppler are used to select 2.7% of the general pregnant population for extended fetal echocardiography.

The effect of ultrasound output level on obstetric biometric measurements

We tested the effect of reducing the ultrasound output energy on obstetric measurements made from two-dimensional (2-D) grayscale images. We measured three fetal structures (femur, umbilical vein and lateral cerebral ventricle) in 113 pregnant women, commencing with an output energy that provided a thermal index for bone (TIB) of ≤1.0, and then repeated the measurements at TIB ≤ 0.5 and then TIB ≤ 0.1. There was a trend toward shorter femur measurements and larger umbilical vein diameter measurements with decreasing output energy. However, since these effects (which did not exceed 0.03 mm) were very small compared with the inter- and intraobserver variations, they were considered to be of no clinical significance. Furthermore, the residuals did not increase when the output energy decreased, indicating that the precision of the measurements was unaltered. We conclude that using a reduced output energy setting corresponding to a TIB of 0.1 does not compromise ultrasound biometry findings.