One of the more common indications for the use of bedside ultrasound (US) is to evaluate patients who present to the emergency department (ED) with pain or bleeding during the first trimester of pregnancy. When performing this study, providers should be aware of several potential pitfalls that pose significant risk to both the patient and the provider.
Background: Ultrasonography during first trimester pregnancy
Emergency medicine (EM) literature and EM professional organizations support the use of bedside US in the evaluation of a first-trimester pregnant patient. McRae et al. found that when providers were able to identify an intrauterine gestational sac with a yolk sac or fetal pole, the specificity of bedside US for identifying an intrauterine pregnancy (IUP) was 92-100%. There was only one case of false positive finding where an ectopic pregnancy was initially categorized as an IUP. Training for providers in the ED involved 10-50 proctored scans in addition to ~10 hours of formal didactics.1 Current ACEP US guidelines call for a total of 80 hours of training in bedside US with a minimum of 2 weeks dedicated. In addition residents must perform a minimum of 150 US scans in “critical” or “life-saving” scenarios.2
Not everyone supports emergency physicians performing this study
There is little agreement between EM, Radiology, and OB/GYN in terms of the training that is necessary to perform first trimester bedside US.3 Compared to ACEP recommendations, training guidelines put forth by the American College of Radiology (ACR), the American College of Obstetrics and Gynecology (ACOG), the American Institute of Ultrasound in Medicine (AIUM), and the Society of Radiologists in Ultrasound (SRU) call for a greater level of exposure in order to obtain competency.4
The AIUM requires evidence of performing, evaluating, and interpreting at least 300-500 sonograms over a 3 year training period comprising a minimum of 3 months of US experience. Once “competency” is achieved, recommendations from the ACR-SPR-SRU joint guidelines and the AIUM states that providers must perform a minimum of 100 diagnostic obstetric USs per year to maintain their skill sets.5
Guidelines from other organizations do not specifically address the specific diagnostic questions that are asked with obstetric US between various specialties. For OB/GYN and radiologists, an obstetric US may be used to evaluate a significant number of parameters and to rule out a wide variety of potential complications. When used in the ED, obstetric US should be used to answer the single binary question: “Is there an intrauterine pregnancy?” It is unclear if, when the scope of the exam is limited to this question, providers could attain competency with less intensive training.
Given a more limited scope of the first trimester pregnancy US exam, EM providers should remember 4 major pitfalls:
1. Beware an “indeterminate” ultrasound
Providers should be cautious of any indeterminate or unclear US findings as these findings are often associated with a high rate of ectopic pregnancy. The definition of an indeterminate pregnancy is heterogeneous in the literature. For the purposes of EM providers, a definition of indeterminate pregnancy may be considered for any US that fails to demonstrate a yolk sac, fetal pole, or fetal heartbeat. Mateer et al. examined the role of emergency provider bedside US in patients who were diagnosed with an ectopic pregnancy after initially being discharged home. All of the discharged patients were noted to have either “abnormal IUP” or “nondiagnostic” findings on their initial US.6
Tayal et al. looked at outcomes of 1,490 patients who underwent a bedside US performed by an EP:7
- 70% were diagnosed with an IUP
- 8% were diagnosed with fetal demise
- 2% were diagnosed with ectopic pregnancy
- Remaining 20% were categorized as “indeterminate”
All non-IUPs underwent a formal US and OB/GYN consultation. Patients who initially had an “indeterminate” US overall had poor outcomes with a 53% rate of fetal demise and 15% rate of ectopic pregnancy. Furthermore 36% of the ectopics required surgical management.
Given this high rate of complications in patients with an initially “indeterminate” US, providers should obtain a formal US study or arrange 48-hour follow up with a gynaecologist in any patient who has findings on bedside US other than a classic IUP.7
2. Beware IUP mimics
In a recent meta-analysis, Stein et al. reported a pooled sensitivity of 99.3%, a negative predictive value of 99.96%, and a negative likelihood ratio of 0.08 for the use of bedside US performed by the ED provider in ruling out an ectopic pregnancy. The authors concluded that the presence of an IUP on bedside US reliably rules out an ectopic pregnancy. Unfortunately there are several scenarios where an abnormal pregnancy may closely resemble an IUP on bedside US which could lead to misdiagnosis. This may include, but not limited to, fetal demise, anembyronic pregnancies, cervical ectopic, or interstitial pregnancies.
Special consideration should be given to cervical ectopic and interstitial pregnancies. Cervical ectopics and interstitial pregnancies account for ~4% of all ectopics yet are associated with an increased risk of significant bleeding, emergency hysterectomy and maternal death. To diagnose these complications providers must be able to identify findings such as irregular placement of the gestational sac or incomplete myometrial mantle. Few ED based protocols address these often subtle findings and in a system where emergency physicians may be credentialed to perform bedside US after 10 proctored scans, these providers may overlook subtle signs that are indicative of an interstitial pregnancy.8,9
3. Beware heterotopic pregnancies
Heterotopic pregnancies, or the presence of both an ectopic and intrauterine pregnancy, are thought to occur in 1 in 4000-30,000 pregnancies during a natural conception cycle. Previous studies have reported a ~5% rate of ectopic pregnancy in patients who are undergoing in-vitro fertilization therapy.10 In patients using assisted reproduction techniques the incidence of heterotopic pregnancy is reported to be as high as 1 in 100.11 Transvaginal US has a reported 56% sensitivity in diagnosing heterotopic pregnancies at 5-6 weeks when performed by certified US technicians.12 To date, there is no data to suggest that ED providers can reliably diagnose heterotopic pregnancy using bedside US. While the exact risk is somewhat unclear, patients using assisted reproductive technology seem to have a significant risk of developing a heterotopic pregnancy. ED providers should obtain a formal US when evaluating these patients due to their risk of heterotopic pregnancy.
4. Beware the BHCG “Discriminatory Zone”
The beta-HCG (BHCG) “discriminatory zone” was originally described in 1981 by Kadar as a means to predict the likelihood of detecting an IUP on US in relation to a quantitative BHCG level.13 In practice, at a BHCG of >1000 IU/mL and 4,000-6000 IU/mL, an IUP should be detectable by trans-vaginal or trans-abdominal US, respectively. Clinicians should NOT use the fact that a BHCG is less than the discriminatory zone cutoff to suggest that an US is not required given the unlikelihood of detecting an IUP on US. It has been documented in the literature of ectopic pregnancies presenting well below traditional discriminatory thresholds, potentially as low as 30 IU/mL.14–16 In addition, a quantitative BHCG level cannot be utilized to rule out the possibility of an ectopic pregnancy or clinically differentiate an ectopic pregnancy from an early IUP.7,17 All patients who present to the ED with a BHCG greater than zero should have an US performed.
Providers need to consider several potential pitfalls when evaluating a pregnant patient using bedside US.
- Clinicians should recognize the focused scope of EM bedside obstetric US such that any indeterminate or unusual findings should be formally evaluated, because these are at higher risk for poor outcomes, such as fetal demise and ectopic pregnancies.
- Any patient who has a significant risk of a heterotopic pregnancy, including those undergoing any type of fertility treatment, should have a formal US performed.
- Any patient presenting with a positive urine BHCG must receive an US even if below the discriminatory zone.
Great topic, Brian and Matt. Some notes:
- Naming the title is actually a tough job. Should be relatively brief and include keywords that would people would Google Search for. So added \"pregnancy\". Numbers are great so \"3\" (which used to be 5) - they are eye-catchy.
- Abbreviations should be consistent and limited to mainstream ones that U.S. and international readers will understand. Would avoid ectopic pregnancy abbreviated as EP, since this is often understood as \"emergency physician\". So I spelled out. There are others which you should just spell out (in red font). Change back to black font when done. I swapped out several others. Furthermore, when you abbreviate something, try to stick with it. Tried to convert as many instances of \"US\" instead of \"ultrasound\".
- The first original pitfall wasn\'t really a pitfall. It was more a lead-up to why there are pitfalls. So I changed to \"background\". The second pitfall was also not a pitfall. So that leaves us with 3 pitfalls.
- There\'s a partial incomplete sentence in red font. Please edit.
- Whenever there is a potential for bulleted lists, that\'s preferred given digital reading styles in a F-style pattern. Lists slow down the reader, who is often skimming the left side of the page and occasionally reading towards the right. So converted some results into a list.
- Conclusions: Are you really recommending that all at-risk patients for ectopic (even history of prior PID) get a formal US? I thought you were advocating for a formal US for just those undergoing assisted reproduction. Need to be ultraclear on this since would hate for people to misinterpret what you are trying to convey.
Please clarify by editing this draft directly responding using this comment system. Thanks!
Thanks for the edits and comments.
- Title sounds good to me.
- I fixed all the uncommon abbreviations.
- I\'m fine with reducing the # of pitfalls, in my mind the fact that our required numbers of scans is so low is somewhat of an issue, but I agree its more of an intro to the problem rather than an actual pitfall.
- Reworded/fixed the incomplete sentence.
- F-Style looks good.
- I changed the conclusion to discuss risk of heterotopic not ectopic. I am somewhat torn in terms of the best recommendation to give when dealing with patients who are at increased risk of ectopic. While features such as previous ectopic, history of PID can significantly increase the risk of ectopic, we don\'t have data to suggest that the rate of heterotopic is actually increased in these patients. So in the ED, most of these folks would show up with an empty uterus and a + HCG which by all existing guidelines should already be categorized as a possible ectopic, I\'m not sure we need to emphasize this scenario within this post.
Expert Peer Review
Overall, this is an excellent summation of the pitfalls of bedside ultrasound in the first trimester of pregnancy. I have a few suggestions for further clarification of pitfall 1, additions to the 2nd pitfall, and the possible addition of a 4th pitfall. I also think it is important to point out that the pitfalls are to be used as an educational tool to improve and encourage the use of bedside ultrasound in the first trimester of pregnancy. The opposite reaction of discontinuing its use secondary to fear is counterproductive and could decrease the quality of patient care.
The first pitfall is excellent, but I feel the point should be made clearer. More emphasis should be placed on the statement that if no IUP or equivalent (Intrauterine yolk sac, fetal pole, intrauterine FHR) is seen, a radiology study or a 48-hour GYN follow-up is a necessity.
While pitfall 2 is a great point, examples of common IUP mimics should be provided. While I understand short and concise is the goal, I feel a brief description of IUP mimics can significantly improve the educational value of the article. Some examples may include the following:
- Irregular Gestational Sacs/Anembryonic Pregnancies – Recognize an abnormal gestational sac and treat as an abnormal pregnancy.
- Fetal Demise – Evaluation of FHR
- Pseudogestational Sac of Ectopic Pregnancy
- Normal appearing fetuses located outside of the uterus – Prior to looking for IUP/FHR, review pelvic landmarks and clearly locate the uterus. After clear recognition of the uterus has occurred, then identify if fetus is intrauterine vs. extrauterine.
- Cervical and Interstitial Ectopics – Consideration of the myometrial mantle size.
Lastly, an additional pitfall may be the discussion of the use of BHCG in first trimester pregnancy. It seems to be a common misconception that a BHCG in the “discriminatory zone” is one that requires no formal study. For instance, a less experienced emergency physician may believe that a BHCG below 1500 is consistent with a very early pregnancy and no ultrasound visualization of an IUP is possible. This may lead to the inappropriate decision to forgo a radiology study for ectopic rule out. However, the more experienced physician understands that ectopic pregnancies routinely produce a disproportionately low BHCG making this lab only relevant in a normal pregnancy. I believe it would be beneficial to make the point that there is no positive BHCG level at which an ectopic pregnancy can be ruled out.
Thank you all for the input. Below is a summary of the changes I have made so far:
- Defined indeterminate pregnancy for clarity of article. I used a simplified EM definition instead of the more detailed ACOG definition to emphasize the binary nature the IUP question (Is there or isn\'t there?) we use for our US studies.
- Clarified recommendations for EPs regarding \"indeterminate\" US findings: must have formal US or very close GYN follow up.
- I have included mention of additional IUP mimics outside of cervical and interstitial pregnancies. I did not go into depth but rather just listed them in order to keep the article on the more concise side. Hopefully by mentioning them, they will be kept in the back of the reader\'s mind.
- I think discussing the BHCG discriminatory zone is very worthwhile and in the scope of the article. I\'ve included it as a 4 pitfall. My focus was on warning the provider against assuming a BHCG below the traditional thresholds does not excuse a US from being performed in a pregnant patient. I also touched on the point that the majority studies that have examined the use of a quantitative BHCG to differentiate an IUP from and ectopic have failed to find a meaningful difference (un-useful as a tool in ED decision making). If any of you feeling pulling out one of this studies to showcase this point would be of value the reader, I\'d be happy to do so.
- I have tidied up errors in the references section.
- I have added a third conclusion on the basis of the 4 pitfall.
Please let me know your thoughts.
Expert Peer Review
Hey Matt/Brian/Michelle - Terrific topic, thanks for inviting me to discussion...
Here are my overall thoughts:
As with most things ‘bedside ultrasound,’ the approach to each modality is typically fundamental. That is to say…for Echo (Is there RV Strain, effusion, a normal EF?)…for Lung (Is there a pneumothorax, effusion, consolidation?). Pointed questions.
Same holds true for TVUS and you guys do discuss this….is there an IUP? The way I learned and I think most fellowships are taught is that if there is any hesitation, uncertainly, unclarity, obtain a consultative formal study.
For a pregnant patient without IVF or hormonal replacement, the chances of correctly identifying an IUP and concomitantly missing an ectopic is in the decimal percentage points (as you allude to). I’m very, very, very comfortable taking this risk. We do things routinely in the ED that carry substantially more risk without much of a second thought (i.e. give penicillin). That said, if the patient is taking supplementation, I will do a TVUS for teaching purposes/learning (with the residents) but always order a consultative ultrasound in tandem. N.B. This patient population also warrants a separate party-line of discharge instructions.
In regards to heterotopic pregnancies, you report a 56% sensitivity for US technicians for detection. This is a flip of a coin. So, while, the risk of a missed heterotopic is real for an ED doctor, it\'s just as real for a radiology department/tech. Thus, this doesn\'t necessarily argue against us as ED docs doing this at the bedside.
Where I do think you may have more of an argument is our ability as ED docs to identify \"low-risk\" vs \"high-risk\" locations of uterine implantation. That is to say, too low or too high in the uterine wall. This isn\'t taught as well across the country and needs to become more of a point of emphasis.
So that’s about it. I’m a firm believer that TVUS for documenting IUP is and will continue to be a modality we should master as ED physicians as long as we know our limitations. As with most things ultrasound, I’m not sure we know what the “right” number of studies is attain competency. I have the residents go straight to transvaginal on all the 1st trimester patients to simply get used to the unique/difficult technique.