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Authors; Kylie Tingley, and Jennifer Horton.
Obstetricians have been using ultrasound to diagnose intrauterine pregnancy since the 1960s and 1970s.1 Ultrasound is a non-invasive diagnostic modality that has typically been associated with little to no risk1; however, epidemiologic research on ultrasound is limited.2 A systematic review by Whitworth and colleagues (2014)3 demonstrated that there is debate in the literature about whether ultrasound examination, especially multiple exposures, is harmful in individuals who are pregnant. Currently, the Society of Obstetricians and Gynaecologists of Canada recommends that all pregnant individuals have 2 ultrasounds; 1 between 11 to 14 weeks’ gestation to date the pregnancy and 1 between 18 to 20 weeks’ gestation to assess anatomic features.4 Despite these recommendations, decision-makers have identified that that pregnant individuals may be receiving additional ultrasounds as part of their routine prenatal care at physicians’ offices and obstetrical clinics, and may also receive an ultrasound during an emergency room visit. This has led to a lack of consistency in the process and there is concern that this has contributed to the potential overuse of ultrasounds during pregnancy.
In response to these concerns regarding the frequent use of ultrasounds during pregnancy, there is a need to review the evidence and evidence-based guidance regarding obstetrical ultrasound to ensure that decision-makers have the best evidence to inform decisions about care pathways for individuals who are pregnant. The 2 objectives of this report are: 1) to identify and summarize the available evidence regarding the safety of routine versus more frequent use of obstetrical ultrasound among individuals who are pregnant; and 2) to identify and summarize the evidence-based guidance regarding the use of obstetrical ultrasound during pregnancy.
A limited literature search was conducted by an information specialist on key resources including MEDLINE, the Cochrane Database of Systematic Reviews, the international HTA database, the websites of Canadian and major international health technology agencies, as well as a focused internet search. The search strategy comprised both controlled vocabulary, such as the National Library of Medicine’s MeSH (Medical Subject Headings), and keywords. The main search concepts were obstetrical ultrasound and adverse events. CADTH-developed search filters were applied to limit retrieval to health technology assessments, systematic reviews, meta-analyses, or network meta-analyses; and randomized controlled trials, controlled clinical trials, or any other type of clinical trial. An additional search was done for obstetrical ultrasound, with CADTH-developed search filters applied to limit retrieval to guidelines. Where possible, retrieval was limited to the human population. The search was also limited to English-language documents published between January 1, 2015 and November 1, 2021.
One reviewer screened citations and selected studies. In the first level of screening, titles and abstracts were reviewed and potentially relevant articles were retrieved and assessed for inclusion. The final selection of full-text articles was based on the inclusion criteria presented in Table 1.
Selection Criteria.
Articles were excluded if they did not meet the selection criteria outlined in Table 1, they were duplicate publications, or they were published before 2015. Guidelines with unclear methodology were also excluded.
The included publications were critically appraised by 1 reviewer using the following tools as a guide: the Appraisal of Guidelines for Research and Evaluation (AGREE) II instrument5 for guidelines. The strengths and limitations of each included publication were described narratively.
A total of 352 citations were identified in the literature search. Following the screening of titles and abstracts, 318 citations were excluded and 34 potentially relevant reports from the electronic search were retrieved for full-text review. Ten potentially relevant publications were retrieved from the grey literature search for full-text review. Of these potentially relevant articles, 34 publications were excluded for various reasons and 10 publications met the inclusion criteria and were included in this report. These 10 publications were evidence-based guidelines. Appendix 1 presents the PRISMA6 flow chart of the study selection.
No eligible health technology assessments, systematics reviews, randomized controlled trials, or non-randomized studies were identified. Ten evidence-based guidelines with recommendations regarding obstetrical ultrasound were identified.2,7-15
Additional details regarding the characteristics of included publications are provided in Appendix 2.
Ten evidence-based guidelines with recommendations regarding obstetrical ultrasound were identified.2,7-15 Six of the guidelines were developed by the Society of Obstetricians and Gynaecologists of Canada,2,8,10-12,15 2 were developed by ISUOG ― the International Society of Ultrasound in Obstetrics and Gynecology,7,14 1 was developed by the U.S. Department of Veterans Affairs and the U.S. Department of Defense,9 and 1 was developed by the American College of Obstetricians and Gynecologists.13 Each of the 10 included guidelines collected evidence using a review of the literature and expert opinion, when needed.2,7-15 One of the guidelines also used patient focus groups to inform their recommendations.9 Five of the included guidelines2,8,10,11,15 used the criteria described by the Canadian Task Force on Preventive Health Care to determine the quality of evidence and classify the strength of recommendations. Evidence was graded from I (evidence obtained from at least 1 randomized controlled trial) to III (opinions of respected authorities and based on clinical experience, descriptive studies, or reports of expert committees). Two guidelines9,12 followed the Grading of Recommendations Assessment, Development and Evaluation system to assess the quality of evidence from high to very low and classify the strength of recommendations as strong or weak. Two guidelines7,14 used an 8-category rating for grading the quality of evidence coupled with a 5-category system for grading the strength of recommendations. Finally, 1 guideline9 followed a method outlined by the United States Preventive Services Task Force to review and evaluate the evidence and assigned 1 of 3 categories to the group’s recommendations.
Six of the included guidelines were Canadian,2,8,10-12,15 2 were from the US,9,13 and 2 were international.7,14
The intended users for each of the 10 included guidelines were health care providers.2,7-15 In half of the included guidelines, the target population broadly covered pregnant individuals.2,7,8,10,13 Two of the guidelines focused on individuals who are pregnant with twins.11,14 One guideline focused specifically on service members or veterans belonging to the U.S. Department of Veterans Affairs or the U.S. Department of Defense and who are pregnant.9 One guideline focused on pregnant individuals with a higher risk of fetal anomalies or who may have complications with a mid-second trimester ultrasound.12 The last guideline focused on pregnant adolescents.15
All 10 guidelines discussed the role of obstetrical ultrasound during pregnancy.2,7-15 Comparators are not relevant to the guideline research question in this report.
The guidelines included in this review provided a series of recommendations related to various outcomes that are of relevance to the use of obstetrical ultrasound and, more broadly, to the management of pregnancy. The outcomes that were considered in the supporting literature for the guidelines included the clinical indications, the benefits and risks of obstetrical ultrasound,2,7,8,10-14 and the monitoring of healthy pregnancy.9,15
The included evidence-based guidelines demonstrated both strengths and limitations. Strengths included the clarity of the scope and purpose for each of the included guidelines, as well as the clarity of presentation for each of the recommendations.2,7-15 Each of the included guidelines were also developed by groups of individuals from all relevant professional organizations.2,7-15 The guidelines also had limitations. Perspectives from members of the target audience (i.e., people who are pregnant) seemed to be present in only 1 of the included guidelines,9 which could limit the applicability of the recommendations.
There were also limitations regarding the rigour of development. While each of the included guidelines included a description of the sources that were searched, it was unclear whether that searching was done in a systematic fashion for 4 of the guidelines.2,7,8,10 One guideline9 adequately described the criteria for selecting the evidence and the methods for formulating the recommendations, whereas in the other 9 guidelines it was unclear from the authors’ reporting how the evidence was selected and how recommendations were developed. In addition, 6 guidelines2,7,8,10-12 did not include discussion of the strengths and weaknesses of the body of evidence used to formulate the recommendations. It was also unclear in 7 of the guidelines2,7,8,10,12-14 whether the recommendations had been externally reviewed by experts before publication. None of the included guidelines provided details of a procedure for updating the guideline. These limitations may limit the certainty of the recommendations provided.
None of the included guidelines2,7-15 discussed barriers or facilitators to the application of recommendations, provided advice or tools that could be put into practice, considered resource implications of applying the recommendations, or presented auditing or monitoring criteria. These limitations may further limit the applicability of the included recommendations. Finally, while each of the included guidelines2,7-15 indicated that competing interests of members of its guideline development group had been recorded, limited information was reported regarding the nature of any competing interests. In addition, the funder for each of the included guidelines2,7-15 was not clearly reported; thus, no comments can be made about potential conflicts of interest concerning the development of the guidelines.
Additional details regarding the strengths and limitations of included publications are provided in Appendix 3.
Appendix 4 presents the main study findings and authors’ conclusions.
No relevant evidence was identified regarding the safety of frequent obstetrical ultrasounds during pregnancy compared to the routine use of obstetrical ultrasound during pregnancy; therefore, no summary can be provided.
This review identified 10 evidence-based guidelines2,7-15 that provided recommendations regarding various clinical indications for obstetrical ultrasound, as well as for the frequency of obstetrical ultrasound during pregnancy.
Van den Hof and colleagues (2019)8 made several recommendations regarding circumstances for when first trimester ultrasound would be warranted. The authors made 4 recommendations for first trimester ultrasound based on evidence that was assessed as good quality: 1) during diagnostic or therapeutic procedures requiring visual guidance (e.g., chorionic villus sampling) and before prophylactic cervical cerclage placement, 2) for suspected multiple gestation, 3) for suspected ectopic pregnancy, molar pregnancy, and suspected pelvic masses, and 4) as a component of the screening protocol for preeclampsia among pregnant people. The guideline development group made an additional 2 recommendations for first trimester ultrasound based on evidence assessed as fair quality: 1) for assessment of threatened abortion, and 2) before pregnancy termination.
The U.S. Department of Veterans Affairs and the U.S. Department of Defense management of pregnancy working group (2018)9 recommended first trimester ultrasound for 3 reasons: to establish gestational age and estimated birth date, to identify multiple pregnancies, and to confirm the presence of cardiac activity. Among those who present with pregnancy after the first trimester, this guideline development group recommends that a dating and anatomical ultrasound be performed at the earliest opportunity and preferably before 22 weeks.9 According to the group’s ranking system, this recommendation was strong and based on moderate-quality evidence.9
Morin and Lim (2017)11 reported specific recommendations for obstetrical ultrasound among people pregnant with twins, stating that a first trimester ultrasound is recommended if a twin pregnancy is suspected at the first physical examination or if the individual is at risk (e.g., those who have used assisted reproductive technologies). The authors made this recommendation based on evidence that was assessed as good quality.11These recommendations align with the previously mentioned guidelines by Van den Hof and colleagues (2019)8 and the U.S. Department of Veterans Affairs and U.S. Department of Defense management of pregnancy working group (2018).9
Cargill and Morin (2017)10 recommended that people who are pregnant be offered a routine second trimester ultrasound between 18 and 22 weeks’ gestation. This recommendation was based on evidence that was assessed by the authors as fair quality.10 Similarly, Morin and Lim (2017)11 recommended that, for people who are pregnant with twins, a detailed ultrasound should be offered and preferably between 18 and 22 weeks’ gestation. Their recommendation was also based on evidence that was assesses to be of fair quality.11 The American College of Obstetricians and Gynecologists (2016)13 also recommended that without other specific indications, the best time for a single ultrasound examination is between 18 and 22 weeks’ gestation. This recommendation was based primarily on consensus and expert opinion.9
Four of the guidelines7,12,14,15 reviewed in this report provided recommendations for specific patient populations for whom increased frequency of obstetrical ultrasound may be warranted.
Khalil and colleagues (2020)7 recommended that serial ultrasound monitoring should be done for the management of maternal and fetal parvovirus B19 infection based on moderate-quality evidence. The authors also recommend that serial ultrasound monitoring be performed for the management of maternal and fetal varicella-zoster virus infection based on low- to moderate-quality evidence, and for maternal and fetal Zika virus infection. However, this recommendation is based on the clinical experience of the guideline development group and is considered a “good practice point.” In addition, Khalil and colleagues (2020)7 recommended that, for those with a Zika virus infection, a third trimester ultrasound should be considered if the baseline scan is normal. However, this recommendation is based on the clinical experience of the guideline development group and is considered a “good practice point.”
Khalil and colleagues (2016)14 recommended that people who have uncomplicated dichorionic twin pregnancies should have a first trimester scan, a detailed second trimester scan, and scans every 4 weeks thereafter. This recommendation was based on the clinical experience of the guideline development group and is considered a “good practice point.” In addition, the authors noted that individuals with complicated pregnancies of dichorionic twins should be scanned more frequently, depending on the condition of the individual and the severity of the complications.14 The authors also recommended that people who are pregnant with monochorionic twins in uncomplicated pregnancies should have a first trimester scan and be scanned every 2 weeks after 16 weeks’ gestation and that complicated cases should be scanned more frequently, depending on the condition and severity of the case.14 These 2 recommendations were based on evidence that the authors assessed as low- to moderate-quality.14
Fleming and colleagues (2015)15 recommended that pregnant adolescents should have a first trimester ultrasound, an anatomical ultrasound at 16 to 20 weeks’ gestation, and an ultrasound to assess fetal well-being and fetal weight at 32 to 34 weeks’ gestation. These recommendations were based on evidence that the guideline development group assessed as good quality.15
Nevo and colleagues (2017)12 recommended that pregnant individuals who have a higher risk for fetal anomalies or for whom a mid-trimester transabdominal ultrasound may be challenging should be offered an early comprehensive fetal anatomic ultrasound at 13 to 16 weeks’ gestation. This ultrasound would not replace the routine 18- to 22-week anatomy scan.12 The recommendation was not graded, but the quality of evidence was rated high (i.e., very confident that the true effect lies close to that of the estimate of the effect).12 It was unclear from the reporting which evidence was used to develop the recommendation.
One guideline2 provided recommendations regarding mitigating the potential harms of obstetrical ultrasound. Van den Hof (2018)2 recommended that ultrasound only be used when the potential medical benefit outweighs any potential risk. According to the ranking system used, this recommendation was based on good-quality evidence.2 In addition, Van den Hof (2018)2 recommended against the use of obstetrical ultrasound for non-medical reasons (e.g., sex determination, non-medical photos, commercial purposes). This recommendation was based on evidence that was assessed by the guideline development group as fair quality.2 The author does make reference to supporting evidence for these recommendations, discussing potential adverse effects of repeat ultrasound exposure during pregnancy.2 Van den Hof (2018)2 also made 2 further recommendations for mitigating the potential harms of obstetrical ultrasound use: ultrasound exposure should be as low as reasonably achievable given the potential for tissue heating if the thermal index exceeds 1 (based on good-quality evidence); and spectral power and colour Doppler should be avoided for imaging in the first trimester, except if the pregnancy is at high risk for trisomy syndromes or anomalies (based on expert opinion of the guideline development group).
No relevant evidence was identified regarding the safety of frequent obstetrical ultrasounds compared to the routine use of obstetrical ultrasound during pregnancy.
Two of the guidelines included in this report were broader in scope than the research question posed by this review (e.g., recommendations for management of pregnancy in specific populations);9,15 thus, the applicability of recommendations may be limited in their generalizability to other populations. Four of the identified guidelines were not developed for the Canadian context and therefore may limit the applicability of recommendations to the Canadian health care system.7,9,13,14
Important methodological limitations were identified in the critical appraisal conducted for the included guidelines, limiting the confidence with which the recommendations can be applied to various clinical settings. In addition, very few of the recommendations were based on high-quality evidence, as reported by the guideline authors. Consequently, the findings of this review should be interpreted with caution.
No relevant studies describing the safety of frequent obstetrical ultrasounds compared to routine versus more frequent use of obstetrical ultrasound were identified; therefore, no summary can be provided. However, this review did identify 10 evidence-based guidelines that included recommendations about various aspects of obstetrical ultrasound use, including clinical indication for obstetrical ultrasound, specific patient populations that may require more frequent obstetrical ultrasound examinations, and strategies to mitigate potential harms of obstetrical ultrasound overuse.
Regarding routine obstetrical ultrasound use, 3 guidelines made recommendations for the use of first trimester ultrasound8,9,11 and 3 guidelines made recommendations regarding the use of second trimester ultrasound, preferably between 18 and 22 weeks’ gestation.10,11,13 Specific patient populations for whom recommendations were made for more frequent obstetrical ultrasound examinations included those with pregnancies who are affected by certain congenital infections,7 people who are pregnant with twins,14 pregnant adolescents,15 and people who are pregnant and at high risk for fetal anomalies or for whom mid-trimester transabdominal ultrasound would be challenging.12 Finally, Van den Hof (2018)2 recommended against obstetrical ultrasound for non-medical purposes (e.g., sex determination, non-medical photos, and so forth) and recommended that ultrasound exposure be as low as possible. Decision-makers should take these recommendations into consideration when developing various care pathways and policies regarding the use and misuse of obstetrical ultrasound.
There is a moderate level of uncertainty regarding the recommendations discussed in this review. Given the important methodological limitations discussed for many of these recommendations, particularly those related to the rigour of guideline development and guideline applicability, and the lack of high-quality supporting evidence available for several of the recommendations, the findings of this review should be interpreted with caution. Better transparency in reporting the methodologies used for guideline development would improve the ability to conduct quality assessment and reduce uncertainties in guideline development.
No evidence regarding the safety of frequent obstetrical ultrasounds compared to the routine use of obstetrical ultrasound were identified. Future research to address this question may help to reduce uncertainty in the frequency of obstetrical ultrasound use during pregnancy and provide decision-makers with better evidence upon which to base their decisions.
Selection of Included Studies.
Characteristics of Included Guidelines.
Strengths and Limitations of Guidelines Using AGREE II.
Note that this appendix has not been copy-edited.
Summary of Recommendations in Included Guidelines.
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