Introduction

All female patients of reproductive age seen in the emergency department (ED) with vaginal bleeding or abdominal or back pain should have a urine or serum pregnancy test performed. Ectopic pregnancy is the number one cause of death in patients in the first trimester.¹ Emergency physicians (EPs) caring for these patients understand that no historical clues or physical findings can effectively affirm or refute an ectopic pregnancy.² The rate-limiting step is finding the location of the pregnancy. Ultrasound imaging and interpretation play a crucial role in this decision-making process. The faster this information is available, the quicker management can be implemented. In the late 1980s, a few EP pioneers invested the time and effort to learn the technical and interpretive skills necessary to bring ultrasound to the bedside.³ The ability to locate a first trimester pregnancy saves valuable time in the search for an ectopic pregnancy.⁴ Ultrasound performed at the patient’s bedside quickly classifies patients by ultrasound criteria.⁵ Based on this ultrasound classification, management strategies can be implemented. The following sections describe the ultrasound techniques and management skills used in symptomatic patients in the first trimester of pregnancy.

Evidence-Based Review

In most EDs, when “formal” ultrasound is traditionally ordered, it is actually performed in the department of radiology. This requires (1) time to transport the patient out of the ED, (2) a sonographer available to obtain the images, and (3) a radiologist to interpret the study. Ultimately, the combination of these factors postpones the diagnosis, delays definitive care, and increase the patient’s length of stay.⁴ As an alternative to formal ultrasound, many EPs have learned how to perform and interpret ultrasound images at the patient’s bedside. As early as 1989, a number of small studies suggested that EPs were able to perform ultrasound for ectopic pregnancies with high sensitivity.³ When previous studies from multiple institutions are compiled to increase the sample size (N = 2057), it is estimated that EPs have a pooled sensitivity of 99.3% when diagnosing ectopic pregnancies at the bedside. Sensitivity is defined as the proportion of bedside ultrasound images demonstrating a true absence of definitive intrauterine pregnancy (IUP) in patients with ectopic pregnancies.⁴

Multiple retrospective and prospective studies from the late 1990s and early 2000s have reported that when compared with formal imaging, the use of bedside ultrasound to evaluate first trimester bleeding reduced length of stay in the ED by a mean time of 48 to 169 minutes. Time of day, day of the week, and whether ultrasound technicians were in house 24 hours a day were some of the factors that had an impact on the length of stay.⁵ Finally, based on two separate studies from the early 2000s, bedside ultrasound performed by EPs saved an estimated $229 to $1244 per ED visit when compared with patients who underwent radiology-performed ultrasound. In some cases this was a 40% savings in billed charges.⁵ Literature from the past 20 years has and continues to demonstrate that ultrasound performed by an EP to evaluate for ectopic pregnancies is feasible, fast, and accurate. Bedside ultrasound in symptomatic first trimester pregnant patients has high sensitivity in ruling out ectopic pregnancy, speeds time to diagnosis, and decreases true costs.

How to Scan

The pelvic organs may be evaluated with one of two different sonographic methods of interrogation: the transabdominal or the endovaginal technique. In the transabdominal approach, the probe is positioned over the lower portion of the abdomen, just superior to the pubic symphysis, and directed inferiorly into the pelvis because the uterus typically remains a pelvic organ until approximately the 12th week of pregnancy. In the endovaginal approach, the probe is inserted into the vaginal vault, directly in touch with the cervix. These “windows” into the pelvis are illustrated and discussed in the following sections.

Transabdominal Technique

The transabdominal technique has long been used to evaluate first trimester pregnant patients and is best done with a curvilinear probe. Before the ultrasound examination, a Foley catheter can be inserted to fill the bladder. The practice of filling the bladder accomplishes two things. First, a full bladder displaces bowel out of the anterior cul-de-sac and acts as an acoustic window to the pelvic organs. Second, a full bladder generally aligns the uterus such that its long axis parallels the abdominal wall. This allows the transmitted sound waves to strike the uterus at a nearly perpendicular angle, which produces better reflections when the returning echoes are received by the transducer and plotted on the monitor. Although this optimizes image quality, adequate images can often be achieved without this maneuver.

In the sagittal view, in which the uterus is seen in its long axis, the probe is placed just superior to the pubic symphysis with the indicator pointed toward the patient’s head. The anterior-most organ on screen is the fluid-filled, triangular-shaped bladder. Just posterior to the bladder is the pear-shaped uterus. The uterus more commonly lies in an anteverted position, with the fundus pointed toward the anterior abdominal wall, but it may also be seen in a retroverted lie with the fundus pointing posteriorly toward the spine. The endometrial stripe serves as the landmark for identifying the longitudinal uterus in the midline. The endometrial stripe is a result of the endometrial mucosal lining coming together to form a hyperechoic, curvilinear line that continues as the cervical stripe more inferiorly (Fig. 120.1, A and B). After the midline of the longitudinal uterus is identified, the probe is panned from side to side to evaluate the entire width of the uterus. Much of the hyperechoic area surrounding the uterus is the bowel and rectum, which are poorly defined because of their solid and gas contents.

Fig. 120.1 A and B, Transabdominal views of the sagittal plane of the uterus revealing the typical landmarks of the uterus, endometrial stripe, cervix, bladder, and vaginal stripe.

In the transverse view, the probe is rotated 90 degrees counterclockwise so that the indicator is pointed toward the patient’s right. With the probe angled inferiorly to visualize into the pelvis, the anterior-most organ is the fluid-filled, rectangular-shaped bladder. Posterior to the bladder is an ovular-shaped cut of the uterus in the transverse view with the hyperechoic endometrial stripe in the center. The rectum and bowel are hyperechoic areas surrounding the bladder and uterus posteriorly and laterally. The uterus should be evaluated from the top of the fundus inferiorly through to the cervix. Though not always visualized, the ovaries may be seen lateral to the fundus of the uterus in either the sagittal or transverse view.

Advantages of the transabdominal technique include (1) an overall view of the true pelvis and (2) a faster examination. The lower-frequency curvilinear probe will penetrate deeper into the pelvis, and although the images might be a little fuzzy, a “full” view of the pelvis is provided. Second, in patients who are farther along in the first trimester or whose bladder is not completely empty, adequate transabdominal views can be obtained without filling the bladder. Less preparation time is needed to scan these patients, and enlisting the assistance of a coworker to chaperone is unnecessary.

The main disadvantage of the transabdominal technique results from the use of a lower-frequency probe. The lower frequency (2- to 5-MHz curvilinear probe) means less resolution and thus the pregnancy must be farther along (usually 7 to 8 weeks’ gestational age) to be visualized. The transvaginal probe is a higher-frequency probe (5 to 9 MHz) with increased resolution, which means that pregnancies as early as 5 to 6 weeks can be visualized.

Endovaginal Technique

The arrival of endovaginal transducers in the 1980s significantly improved the quality of ultrasound imaging in female patients. Simplified, the engineering design placed an ultrasound transducer on the end of a stick that could be inserted into the vaginal vault. This permits the transducer scanning head to be in close proximity to the pelvic organs, which has several important implications in ultrasound imaging. First, there is a clearer path to transmit and receive echoes, and second, the shorter distance between the transducer and the pelvic organs allows higher transducer frequencies to be used.⁶ In contrast to the transabdominal approach, the quality of images from an endovaginal approach is enhanced with an empty bladder because of less distortion of the pelvic anatomy.

The high-frequency endocavitary probe is prepared by directly placing ultrasound gel on the transducer head, sheathing the probe with a sterile cover, and then adding more sterile gel over the sheathed transducer head. If it is not possible to place the patient in the lithotomy position on a gynecology examination table, it is important to adequately prop up the patient’s pelvis for any modified positioning. It is often necessary to manipulate the handle of the probe below the level of the pelvis for better visualization. The covered probe is then inserted into the vaginal vault to begin scanning. Some patients and practitioners have found it more comfortable for patients to insert the probe.

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