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William T. Hosek, M.D., FACEP

I.  Introduction and Indications

One in every thirteen women presenting to the emergency department in their first trimester of pregnancy with abdominal or pelvic pain or vaginal bleeding will eventually be diagnosed with an ectopic pregnancy.(1-4) Because the history and physical exam has proven to be unreliable in detecting or excluding the presence of an ectopic pregnancy(2,4), ultrasound has become more than just an adjunctive diagnostic tool.  Traditionally, the serum quantitative B-hCG has been the initial test performed in the evaluation for possible ectopic pregnancy.  Only if the quantitative B-hCG level was above a certain level was pelvic ultrasound performed.(4)  Unfortunately, limiting the use of ultrasound in this way results in delayed diagnosis of ectopic pregnancy, a great number of undiagnosed ectopic pregnancies being released from the ED, and a significant number of ectopic pregnancies rupturing prior to definitive treatment.  Ultrasound as the initial step in the evaluation of all women presenting to the ED in their first trimester with abdominal pain or vaginal bleeding provides the best chance of early diagnosis of ectopic pregnancy.(5,6,7)  Given the financial and logistical challenges of providing resources for around-the-clock immediate ultrasound, clinician-performed pelvic sonography has been incorporated into the practice of emergency medicine.(8)  Pelvic ultrasound performed by emergency physicians significantly reduced emergency department length of stay for those women found to have an intrauterine pregnancy and has reduced the incidence of discharged patients with subsequent ectopic pregnancy rupture.(5,9,10)

II.  Anatomy

Uterus
The uterus is a pear-shaped organ that lies posterior to the bladder and anterior to the sigmoid colon.  The uterus consists of the body, an upper broad fundus and the lower neck or cervix.  The size of the uterus in the adult (post-pubertal) female is approximately 8 cm long, 5 cm wide and 3 cm deep.  The uterus is composed of three layers which include the outer serosa, a muscular middle layer and the inner endometrium.  The uterine fundus may point towards the anterior abdominal wall (anteverted) or back towards the spine (retroverted).  When a sharp angle exists between the cervix and fundus, the uterus is said to be flexed.

Fallopian Tubes and Ovaries
Each fallopian tube is approximately 10 cm in length and consists of four segments (from proximal to distal: the interstitial cornu, isthmus, ampulla and infundibulum).  Ovaries are elliptical and approximately 4 cm in length, 3 cm in width and 2 cm in height.  Although the location of the ovaries can vary, they are usually anterior to the internal iliac artery.(11)

III.  Scanning Technique and Normal Findings

Transabdominal Ultrasound
The goal of pelvic ultrasound is to scan completely through the uterus and adnexal region in both the longitudinal and transverse planes.  The transabdominal ultrasound employs ideally a 3.5 MHz curvilinear probe and begins just above the pubic symphysis in a longitudinal axis.  It is best performed when the patient has a full bladder, which tends to displace overlying bowel away from penetrating ultrasound waves (Figure 1, illustration 1).

 

	Figure 1		Illustration 1

The endometrial lining appears as an echogenic line on ultrasound (the endometrial stripe) and identifies the center of the uterus in the longitudinal plane.  The ultrasound probe is moved laterally from side to side through the entire width of the uterus in the longitudinal plane looking for evidence of an intrauterine pregnancy.  The probe is next placed in the transverse plane just above the pubic symphysis directed down towards the uterus (Figure 2 and illustration 2).

	Figure 2		Illustration 2

Figure 2:  Transabdominal ultrasound in a transverse plane showing bladder, uterus and right ovary.
Illustration 2:  Drawing of corresponding anatomy.

Once the endometrial stripe is identified, the uterus is scanned from cervix to fundus in the transverse plane.  Finally, although not often visualized in the transabdominal ultrasound, the ovaries are located by sweeping laterally from the uterus.  Before moving on to the transvaginal ultrasound, the hepatorenal space should be scanned for the presence of free fluid which appears anechoic when present.  It is important to remember that the ultrasound is providing the clinician with one thin slice through a given region.  Therefore, free fluid may be missed if a region is not thoroughly scanned.

Transvaginal Ultrasound
The transvaginal ultrasound is best performed on patients with an empty bladder because of reduced patient discomfort, reduced uterine distortion from the distended bladder and less artifacts.  The transvaginal probe is typically a 5 MHz probe and is covered with a probe condom.  Bacteriostatic Surgi-lube is placed inside and outside of the condom to ensure smooth transmission of ultrasound waves.  Some patients experience less discomfort when they place the probe into the vaginal canal by themselves.  The probe is placed adjacent to the cervix (Illustration 3).  A transvaginal ultrasound in the longitudinal axis will appear as shown in figure 3.  In this standardized format, a uterine fundus pointing towards the anterior abdominal wall is anteverted.  A uterine fundus pointing in the direction of the posterior wall is retroverted (Figure 4, video clip 1).  The longitudinal scan begins midline at the endometrial stripe and the uterus is scanned from right to left through its entire length (Video clip 2).  The probe is then moved laterally to the adnexal area to view the ovaries.

	Figure 3		Illustration 3

Figure 3:  Transvaginal ultrasound in a longitudinal plane showing an anteverted uterus.
Illustration 3:  Drawing of longitudinal view of uterus with pelvic probe in canal.

Figure 4:  Transvaginal ultrasound in a longitudinal plane showing a retroverted uterus.

Video clip 1: Pelvic video of a retroverted uterus.

Video clip 2:  Pelvic scan of uterus in longitudinal plane.

Once scanning is complete in the longitudinal axis, the probe is rotated 90 degrees counterclockwise so that the probe is now in the transverse plane (illustration 4).  In this orientation, the left side of the screen corresponds to the patient’s right side (similar to what is seen with a CT scan).  The transverse scan begins with identification of the endometrial stripe and then moves throughout the entire length of the uterus (Figure 5).  In order to help locate the ovaries, the cornual flare, the portion of the uterus at the junction of the fallopian tubes, is identified (Figure 6).  Once the cornual flare is located, the probe is moved laterally along the fallopian tube to locate the ovary (Video clip 3).  Ovaries are often identified by the presence of follicles, which appear hypoechoic or anechoic (Figure 8 and 9).

Illustration 4:  Drawing of the transverse view of the uterus with probe in vaginal canal.

Video clip 3:  Transvaginal scan showing the fallopian tube and ovary.

Figure 5:  Transverse uterus with endometrial stripe.

	Figure 6		Figure 7

Figure 6:  The same transvaginal ultrasound with marking of the cornual flare (uterine fundus at the start of the fallopian tube).
Figure 7:  Transvaginal ultrasound of the fallopian tube.

	Figure 8		Figure 9

Figure 8 and 9:  Transvaginal ultrasound of the ovary showing multiple (Figure 8) and a single follicle (Figure 9).

Intrauterine Pregnancy
The first question to ask when evaluating a patient with pain or bleeding in their first trimester pregnancy is “Is there evidence of a definitive intrauterine pregnancy on ultrasound?”  The presence of an intrauterine pregnancy virtually rules out ectopic pregnancy in patients not receiving fertility medication.  Fortunately, this occurs in approximately 70% of cases presenting to the emergency department. 

The earliest sign of pregnancy on transvaginal ultrasound is the intradecidual sign, an anechoic sac without a distinct chorionic ring. This may be seen as early as four weeks gestation (Figure 10 and 11).  However, definitive sonographic evidence of an intrauterine pregnancy is confirmed when a gestational sac containing a yolk sac can be identified in two planes within the endometrium.  This occurs around the fifth week of gestation (Figure 12 and 13).

Figure 10:  Transvaginal ultrasound in longitudinal plane showing an anechoic sac within the endometrium.

Figure 11:  Transvaginal ultrasound in transverse plane (magnified) showing an anechoic sac with a thin ring (decidual sac).

	Figure 12		Figure 13

Figure 12 and 13:  Transvaginal ultrasound in a longitudinal (Figure 12) plane and transverse plane (Figure 13) showing a gestational sac containing a yolk sac within the endometrium (viable IUP).

At six weeks gestation, the heart tubes of the embryo fuse and both a fetal heart beat as well as a fetal pole can be identified (Figure 14 and 15).  At seven weeks gestation, the fetal head and extremities can be identified.  The amniotic sac is often seen as it begins to expand into the chorionic sac (Figure 16).  Ten weeks gestation marks the end of the embryonic period, and on ultrasound, the amniotic sac will obliterate the chorionic sac (not quite complete in Figure 17).

	Figure 14		Figure 15

Figure 14:  Transvaginal ultrasound: gestational sac with yolk sac and fetal pole.
Figure 15:  Transvaginal ultrasound with Doppler over the fetal pole showing the presence of a fetal heart beat (viable IUP).

	Figure 16		Figure 17

Figure 16:  Transvaginal ultrasound at 7 weeks gestation.
Figure 17:  Transvaginal ultrasound at 10 weeks gestation (end of the embryonic period).

The introduction of fertility medications has greatly increased the incidence of multiple gestations.  Figure 18 is a transvaginal ultrasound in the transverse plane showing dichorionic, diamniotic twin gestations.  The ultrasound shows two separate gestational sacs (i.e. dichorionic), each with its own yolk sac (i.e. diamniotic) and fetal pole. 
Multiple gestations are by their very nature high risk pregnancies.  In addition, the incidence of heterotopic pregnancy (simultaneous intrauterine and ectopic pregnancy) has dramatically risen with fertility treatments.  Therefore, early obstetrical consultation should be considered in any patient with either multiple gestations or who has received fertility treatments.

Figure 18:  Transvaginal ultrasound showing twin gestations with two separate gestational sacs (dichorionic) and two yolk sacs (diamniotic).

IV.  Pathologic Findings
Abnormal Pregnancy
Signs suggestive of abnormal embryonic development include a gestational sac greater than 8 mm in diameter without a visible yolk sac (Figure 19), a gestational sac greater than 18 mm in diameter without a fetal pole (Figure 20), or a collapsed gestational sac (Figure 21).  Additionally, absence of a fetal heart beat in an embryo with a crown rump length of 5 mm (Figure 22) or a fetal heart beat less than 90 beats per minute are poor prognostic signs.  Gestational trophoblastic disease (i.e. molar pregnancy) may present with multiple, small, irregular cystic lesions within the endometrium (Figure 23 and 24).

	Figure 19		Figure 20		Figure 21

Figure 19:  Transvaginal ultrasound in a longitudinal plane shows a gestational sac greater than 8 mm diameter without a yolk sac (fetal demise). Figure 20:  A gestational sac greater than 18 mm without a fetal pole (fetal demise).
Figure 21:  Transvaginal ultrasound in a longitudinal plane showing a collapsed gestational sac (fetal demise).

Figure 22:  Transabdominal ultrasound with Doppler showing the absence of fetal heart tones in an eight-week gestational pregnancy (fetal demise).

	Figure 23		Figure 24

Figure 23 and 24:  Transverse (23) and longitudinal plane ultrasound (24) showing gestational trophoblastic disease.

Ectopic Pregnancy
Definitive diagnosis of ectopic pregnancy requires visualization of a fetal heart beat outside the uterus.  Figure 25 shows a gestational sac with a fetal pole.  A fetal heart beat was detected on ultrasound exam.  On closer inspection, the gestational sac was clearly outside the endometrial cavity indicating an ectopic pregnancy.

Figure 25:  Transvaginal ultrasound in a longitudinal plane showing an ectopic gestational sac.

An ectopic fetal heart beat is identified in only a small percentage of the total number of ectopic pregnancies.  In approximately 28% of patients presenting to emergency department, neither a definitive intrauterine pregnancy nor a definitive ectopic pregnancy can be visualized by ultrasound.  In these cases, diagnosis of ectopic pregnancy is often reached through a combination of abnormal sonographic findings.

Absence of a Definitive Intrauterine Pregnancy
Once the absence of a definitive intrauterine pregnancy has been established, correlation with a serum B-hCG is the next step.  Transvaginal ultrasound should detect the presence of a normal IUP when the serum B-hCG exceeds 1000 mIU/ml.  Given the incidence of ectopic pregnancy in women presenting early to the ED with pelvic complaints, lack of a definitive IUP is quite concerning.  A quantitative B-hCG above 1000 mIU/ml without evidence of a definitive intrauterine pregnancy implies either a recently aborted pregnancy or an ectopic pregnancy.  While the presence of an intradecidual sac might indicate an early pregnancy, it could also represent endometrial breakdown in the presence of an ectopic pregnancy (the pseudo-gestational sac).  Figure 26 shows a longitudinal view of the uterus with a pseudogestational sac.  The endometrial sac does not have a surrounding chorionic ring and free fluid is visible in the posterior cul-de-sac.  This patient had a ruptured ectopic pregnancy.

Figure 26:  Transvaginal ultrasound in a longitudinal plane showing pseudo-gestational sac.

Free Fluid
The presence of free fluid is a frequent normal physiologic finding in women.  Figure 27 is a transabdominal ultrasound in the transverse plane across the uterus, which shows a small amount of physiologic free fluid in the pelvic cul-de-sac.

Figure 27:  Transabdominal ultrasound in the transverse plane showing free fluid in the pelvic cul-de-sac.

However, free fluid is also associated with both ruptured (more commonly) and unruptured ectopic pregnancies.  In addition, the likelihood of rupture increases with the increase in quantity of free fluid.(12)  Since clotted blood in the pelvic cul-de-sac after tubal rupture can sometimes obscure the ultrasound image, a brief scan through the hepatorenal space can often lead to quick identification of active hemorrhage.  In the first trimester, the presence of free fluid in the hepatorenal space of a patient without an intrauterine pregnancy is virtually diagnostic of a ruptured ectopic pregnancy.(13) Figure 28 shows a large amount of free fluid in and around the hepatorenal space in a patient with a ruptured ectopic pregnancy.  Despite the amount of hemorrhage, free fluid was not readily seen on transvaginal ultrasound because of distorted landmarks from clotted blood (Figure 29).

	Figure 28		Figure 29

Figure 28:  Ultrasound of the hepatorenal space (ruptured ectopic) demonstrating anechoic (black) free fluid between the liver and right kidney. Figure 29:  Transvaginalultrasound in a longitudinal plane (ruptured ectopic).

Tubal Rings
Figures 30 and 31 are ultrasounds of unruptured tubal ectopic pregnancies.  Both ultrasounds show a gestational sac surrounded by a thick chorionic ring outside and immediately adjacent to the myometrium.

	Figure 30		Figure 31

Figure 30:  Transvaginal ultrasound in a longitudinal plane with unruptured ectopic.Figure 31:  Transvaginal ultrasound
showing a ring-like structure situated between the left ovary and uterus.

A Complex Adnexal Mass
The presence of coagulated blood surrounding a ruptured ectopic can distort the sonogram, making the diagnosis challenging.  Even in the absence of hemorrhage, a gestational sac may not be well-defined and a distinct echogenic ring may not be present.  Figure 32 is a transverse transvaginal ultrasound of the fallopian tube showing a suspicious adnexal mass found to be an unruptured ectopic pregnancy in the operating room.  These findings will usually only be picked up with transvaginal ultrasound.

Figure 32:  Transvaginal ultrasound in a transverse plane showing a suspicious adnexal mass.

An Eccentrically Located Pregnancy
A gestational sac surrounded by less than 5 mm of myometrium suggests ectopic pregnancy.  In addition, a gestational sac with a marked eccentric location in the uterus is often suggestive of ectopic pregnancy.  Figure 33 is a transvaginal ultrasound in the transverse plane showing a large eccentrically located mass in the uterus.  This was found to be a left interstitial pregnancy in the operating room.

Figure 33:  Transvaginal ultrasound in a transverse plane showing an interstitial pregnancy.

Color Doppler
The improved capabilities of smaller, more portable ultrasound machines or systems now give emergency physicians the option of color Doppler use in the evaluation of first trimester pregnancy.  Since an implanted gestational sac has increased blood supply, identifying vascular asymmetry in the adnexal areas may allow for a specific diagnosis in cases where an ultrasound without color Doppler were previously ruled “non-diagnostic”.  Similarly, color Doppler could potentially aid in distinguishing an early intrauterine gestational sac with its surrounding blood supply from that of a pseudogestational sac.  Figure 34 is a transvaginal ultrasound in the transverse plane showing a normal right fallopian tube.  Here, color Doppler has identified the fallopian tube just anterior to the iliac vessels.  Blood supply above the iliac vessels in the area of the fallopian tube is normal.  Marked increase in color flow (blood flow) of the contra lateral adnexal region would suggest the presence of an embedded ectopic pregnancy.

Figure 34:  Transvaginal ultrasound of the right fallopian tube in a transverse plane using color Doppler.

The use of Spectral Doppler interrogation can also be used to distinguish placental blood flow from maternal blood flow in suspicious adnexal masses, early intrauterine pregnancy, and recent fetal demise with retained intrauterine products of conception.  Figure 35 shows spectral Doppler interrogation of a normal ovary.  Although large trials with emergency physicians utilizing color Doppler in the evaluation of patients in their first trimester pregnancy are lacking to date, case reports have supported the use of color Doppler in this way. (13)

Figure 35:  Transvaginal ultrasound of the ovary with color Doppler interrogation and pulsed Doppler (= spectral Doppler).

It should be noted that although no adverse effects to a fetus have ever been shown, ultrasound does have the potential for mechanical bioeffects.  Additionally, color Doppler is considered a higher intensity ultrasound and carries a higher potential risk of adverse effects than ultrasound without color Doppler.  Therefore, the goal when using ultrasound is to obtain the most diagnostic information at the lowest possible output level. Fortunately, in the majority of cases a definite intrauterine pregnancy can be established without the need for color Doppler.  In cases where ultrasound is “non-diagnostic” (approximately 28% of the time), color Doppler may prove useful in enhancing the sensitivity of a “diagnostic” ultrasound.
           

V.  Pearls and Pitfalls Using the serum quantitative B-hCG to decide when to perform an ultrasound. Not performing the ultrasound. Interpreting an early gestational sac as definitive evidence of an intrauterine pregnancy. Not visualizing the gestational sac in two planes. Not performing an ultrasound of the hepatorenal space for free fluid. Not identifying an eccentrically located gestational sac. Diagnostic ultrasound including its use in pregnancy has an impressive safety record.  Laboratory studies have shown that diagnostic levels of ultrasound can produce physical effects in tissue, also called “bioeffects”.  These effects include mechanical vibrations, cavitation and heat.  Safety guidelines promoting limited exposure time and ultrasound intensity have therefore been implemented to avoid adverse effects, especially in the fetus.(14)

 

VI.  References

1  Stovall TG, Kellerman AL, Ling FW, Buster JE.
Emergency department diagnosis of ectopic pregnancy. Ann Emerg Med.1990;19(10):1098-103.

2  Kaplan BC, Dart RG, Moskos M, Kuligowska E, Chun B, Adel Hamid M, Northern K, Schmidt J, Karwadkar A.
Ectopic pregnancy: Prospective study with improved diagnostic accuracy. Ann Emerg Med.1996;28:10-17.

3 Buckley RG, King KJ, Disney JD, Gorman JD, Klausen JH.
History and physical examination to estimate the risk of Ectopic pregnancy: Validation of a clinical prediction model. Ann Emerg Med.1999;34:589-594.

4  Barnhart K, Mennuti MT, Benjamin I, Jacobson S, Goodman D, Coutifaris C.
Prompt diagnosis of ectopic pregnancy in an ED setting. Obstet Gynecol.1994;84(6):1010-15.

5  Mateer JR, Valley VT, Aiman EJ, Phelan MB, Thoma ME, Kefer MP.
Outcome analysis of a protocol including bedside endovaginal sonography in patients at risk for ectopic pregnancy. Ann Emerg Med.1996;27:283-289.

6  Kaplan BC, Dart RG, Moskos M, Kuligowska E, Chun B, Adel Hamid M, Northern K, Schmidt J, Kharwadkar A.
Ectopic pregnancy: Prospective study with improved diagnostic accuracy. Ann Emerg Med.1996;28:10-17.

7  Gracia CR, Barnhart KT.
Diagnosing ectopic pregnancy: Decision analysis comparing six strategies. Obstet Gynecol.2001;97:464-70.

8  Mateer J, Plummer D, Heller M, Olson D, Jehle D, Overton D, Gussow L.
Model curriculum for physician training in emergency ultrasonography. Ann Emerg Med.1994;23:95-102.

9  Shih CH.
Effect of emergency physician-performed pelvic sonography on length of stay in the emergency department. Ann Emerg Med.1997;29(3):348-351.

10  Blaivas M, Sierzenski P, Plecque D, Lambert M.
Do emergency physicians save time when locating a live IUP with bedside ultrasonography? Acad Emerg Med.2000;7(9):988-93.

11  Reardon RF, Martel ML.
First trimester pregnancy. In: Ma OJ, Mateer JR (eds.). Emergency Ultrasound. McGraw-Hill: New York.2003;239-275.

12  Dart R, McLean S, Dart L.
Isolated fluid in the cul-de-sac: How well does it predict ectopic pregnancy?
Am J Emerg Med.2002;20:1-4.

13  Blaivas M.
Color doppler in the diagnosis of ectopic pregnancy in the emergency department: Is there anything beyond a mass and fluid? J Emerg Med.2002;22(4):379-384.

14  AIUM.
Bioeffects and safety of diagnostic ultrasound. AIUM,1993.11200 Rockville Pike, Suite 205, Rockville, Maryland 20852-3139, USA.