Literature Canon Update from the ACEP Emergency Ultrasound Fellowship Education Subcommittee: Obstetrics

Trent T. She, MD, FACEP
Hartford Hospital, University of Connecticut
Di Coneybeare, MD, MHPE
Columbia University Medical Center, Vagelos School of Physicians and Surgeons
Alexis Salerno, MD, FACEP
University of Maryland, School of Medicine
Sandy Werner, MD, FACEP
MetroHealth Medical Center, Case Western Reserve University

The subcommittee would like to acknowledge the following individuals for their contributions to this literature canon review:

Lindsay Davis, MD; Judy Lin, MD, FACEP; Bannet Muhoozi, MD; Mark Sheatzle, MD, FACEP’ Emily Cen, MD; Harold Gomez Acevedo, MD, FACEP

Content

The ACEP Ultrasound Section’s Fellowship Education Subcommittee continues to put together and expand on our Literature Canon of the need-to-know articles in point-of-care ultrasound.

For more information on how the Literature Canon was borne and how articles were selected, see this article here.

The following were the top 5 articles in Obstetrics as selected by the Fellowship Education Subcommittee.

Obstetrics Top 5 Articles

1. Tayal VS, Cohen H, Norton HJ. Outcome of patients with an indeterminate ED first‐trimester pelvic ultrasound to rule out ectopic pregnancy. Acad Emerg Med. 2004;11(9):912-7.

Summary: In first-trimester pregnant patients presenting to the emergency department (ED) with abdominopelvic pain or vaginal bleeding, indeterminate point-of-care ultrasound (POCUS) for an intrauterine pregnancy (IUP) was often associated with an eventual non-viable pregnancy.

This 2004 study was a single-center, prospective observational study over a 13-month period at a large tertiary care ED seeing 100,000 patients/year. Consecutive patients were enrolled. Inclusion criteria were first-trimester pregnant patients presenting with abdominal pain, pelvic pain or vaginal bleeding. 95% of all first-trimester ultrasounds were performed by clinical emergency physicians with a Shimadzu 450XL machine. Both transabdominal and, if needed, transvaginal imaging was obtained. An indeterminate ultrasound was defined as an ultrasound not demonstrating an IUP, ectopic pregnancy, molar pregnancy or fetal demise. Indeterminate ultrasound were followed by close 48-hour outpatient followup or operative intervention (including endometrial sampling).

1,490 patients were in the final analysis. 300 (20%) had an initial indeterminate ultrasound. Of this subset, only 88 (29%) ultimately had an IUP. 158 (53%) had fetal demise, 44 (15%) had an ectopic pregnancy, and 10 (3%) were lost to follow-up.

1. Doubilet PM, Benson CB, Bourne T, Blaivas M. Diagnostic criteria for nonviable pregnancy early in the first trimester. N Engl J Med. 2013;369(15)1443-51.

Summary: This is a review article summarizing the sonographic diagnostic criteria of first trimester non-viable pregnancy.

In this 2013 review article, patients with no visualized IUP on ultrasound, a single serum hCG level cannot distinguish between an ectopic, nonviable or viable pregnancy. Use of “a discriminatory zone” of hCG level is not advised.

In patients with an established IUP, the following were diagnostic for a nonviable pregnancy:

• Crown–rump length of ≥7 mm and no heartbeat
• Mean sac diameter of ≥25 mm and no embryo
• Absence of embryo with heartbeat ≥2 wk after a scan that showed a gestational sac without a yolk sac
• Absence of embryo with heartbeat ≥11 days after a scan that showed a gestational sac with a yolk sac

In patients with an established IUP, the following were suggestive of a nonviable pregnancy:

• Crown–rump length of <7 mm and no heartbeat
• Mean sac diameter of 16–24 mm and no embryo
• Absence of embryo with heartbeat 7–13 days after a scan that showed a gestational sac without a yolk sac
• Absence of embryo with heartbeat 7–10 days after a scan that showed a gestational sac with a yolk sac
• Absence of embryo ≥6 wk after last menstrual period
• Empty amnion (amnion seen adjacent to yolk sac, with no visible embryo)
• Enlarged yolk sac (>7 mm)
• Small gestational sac in relation to the size of the embryo (<5 mm difference between mean sac diameter and crown–rump length)

1. Richardson A, Gallas I, Dobson S, Campbell BK, Coomarasamy A, Raine-Fenning N. Accuracy of first‐trimester ultrasound in diagnosis of tubal ectopic pregnancy in the absence of an obvious extrauterine embryo: systematic review and meta‐analysis. Ultrasound Obstet Gynecol. 2016;47(1): 28-37.

Summary: In this meta-analysis, the presence of an empty uterus, a pseudosac, an adnexal mass and free intraperitoneal fluid demonstrated excellent specificity but not sensitivity in the diagnosis of tubal ectopic pregnancy.

This 2016 meta-analysis of 31 total prospective studies encompassed 5,858 women from 1987-2005. Only primary studies of ≥ 10 patients that reported a sonographic diagnosis of ectopic pregnancy were included. It is not specified in the meta-analysis as to whether the patients were seen in the ED or if the ultrasounds were performed by the department of radiology, obstetrics or emergency medicine.

For predicting a tubal ectopic pregnancy, the following sonographic signs were assessed for in the meta-analysis:

• An empty uterus showed a sensitivity of 81.1% and specificity of 79.5% (13 studies, 2499 patients)
• A pseudogestational sac showed a sensitivity of 5.5% and specificity of 94.2% (8 studies, 1838 patients)
• An adnexal mass showed a sensitivity of 63.5% and specificity of 91.4% (21 studies, 2787 patients)
• Free fluid (not explicitly free abdominal or pelvic fluid) showed a sensitivity of 47.2% and specificity of 92.3% (19 studies, 3232 patients)
• 7 studies looked at the presence of an adnexal mass and free fluid in 1023 total patients showing a sensitivity of 45% and specificity of 96%
• 1 study, featuring 265 patients, looked at the presence of:
  • Adnexal mass and pseudogestational sac showed sensitivity of 2.9% and specificity of 100%
  • Free fluid and pseudogestational sac showed sensitivity of 3.9% and specificity of 96.6%
  • Adnexal mass and pseudogestational sac and free fluid showed sensitivity of 5.8% and specificity of 100%

1. Dart RG, Burke G, Dart L. Subclassification of indeterminate pelvic ultrasonography: prospective evaluation of the risk of ectopic pregnancy. Ann Emerg Med. 2002;39(4):382-8. (subscriber link only)

Summary: In this prospective, single-center observational study of patients with first-trimester abdominal pain or vaginal bleeding and an indeterminate ultrasound for IUP, an empty uterus was associated with an ectopic pregnancy 13.9% of the time compared and was the most common sonographic finding in an ectopic pregnancy.

This 2001 prospective study in an academic ED seeing approximately 60,000 patients/year starting in 1/1/1995 to 8/31/2000. Patients were included if they had abdominal pain or vaginal bleeding, had a positive hCG test (serum or urine) and had an indeterminate ultrasound for an intrauterine or ectopic pregnancy. Any patients who had a prior ultrasound confirming an intrauterine or ectopic pregnancy, had a recent delivery or procedure, or were lost to follow-up were excluded.

Ultrasounds were performed by the radiology department. Acuson 128 and ATL Ultramark 9 HDI machines were used. Study investigators classified ultrasounds into 5 subclasses: empty uterus, nonspecific intrauterine fluid, intrauterine echogenic material, an abnormal appearing gestational sac and a normal appearing gestational sac. Study investigators then looked at the final diagnosis of these patients and classified them into 4 subclasses: normal IUP, abnormal IUP, indeterminate (abnormal vs normal IUP), ectopic pregnancy.

635 patients were in the final analysis of which 476 patients had an abnormal IUP (75%) which would not reach term and 46 had an ectopic pregnancy (7.2%). Of the patients with ectopic pregnancy, the most common sonographic finding in this population was by far an empty uterus (36/46, relative risk 5.2), followed by nonspecific intrauterine fluid (6/46) and intrauterine echogenic material (4/46). No patients with a defined gestational sac were found to have ectopic pregnancy.

In a subgroup analysis, 38/46 ectopic pregnancies had a serum hCG level < 1000 while 8/46 ectopic pregnancies had a serum hCG level > 1000. The authors noted a low serum hCG level should not be considered reassuring in the presence of an empty uterus, and may be more indicative of an ectopic pregnancy.

1. Tabbut M, Harper D, Gramer D, Jones R. High-frequency linear transducer improves detection of an IUP in first-trimester ultrasonography. Am J Emerg Med. 2016;34(2):288-291. (subscriber link only)

Summary: In this prospective, single-center convenience sample of 88 first-trimester pregnant patients, 27 of those 88 did not have an IUP visualized transabdominally with a curvilinear probe. 9 of these 27 patients had an IUP visualized with a subsequent transabdominal scan via a linear probe.

This is a 2015 single center-prospective, convenience, pilot study at an academic ED with more than 100,000 patients/year with a residency and ultrasound fellowship. Patients were included if they were in their first trimester of pregnancy, if they had a positive pregnancy test and did not have a prior ultrasound. The majority of images were obtained by an ultrasound fellow or emergency medicine residents during the hours of 8am-5pm due to the presence of an ultrasound team. Philips HD11 or Philips Sparq machines were used.

81 patients were in the final analysis. 54 (66.7%) definitive pregnancies were visualized (1 ectopic) via a transabdominal scan with a curvilinear probe. Of the 27 non-definitive pregnancy locations, 9 patients were found to have an IUP with a subsequent transabdominal scan with a linear probe. Of the remaining 18 patients that needed a transvaginal ultrasound (performed by either radiology or the ED), only 3 had a confirmed IUP.