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Clinical Procedures > Radiology
Bedside Ultrasonography, First-Trimester Pregnancy
Article Last Updated: Jan 8, 2008
AUTHOR AND EDITOR INFORMATION
Section 1 of 12  
Author: Timothy Jang, MD, Director of Emergency Ultrasound, Olive View-UCLA Medical Center, Clinical Faculty, Division of Emergency Medicine, Washington University School of Medicine
Coauthor(s):
Jennifer C Chen, MD, MPH, Staff Physician, Departments of Internal Medicine and Emergency Medicine, University of California at Los Angeles/Olive View Medical Center
Editors: James Quan-Yu Hwang, MD, Attending Physician, Department of Emergency Medicine, Brigham & Women's Hospital; Clinical Instructor, Harvard Medical School; Mary L Windle, PharmD, Adjunct Assistant Professor, University of Nebraska Medical Center College of Pharmacy, Pharmacy Editor, eMedicine.com, Inc; Rick Kulkarni, MD, Medical Director, Assistant Professor of Surgery, Section of Emergency Medicine, Yale-New Haven Hospital
Author and Editor Disclosure
Synonyms and related keywords:
first-trimester vaginal bleeding, ectopic pregnancy, pelvic ultrasound, obstetric ultrasound, ultrasonography, Doppler, pelvic ultrasonography, obstetric ultrasonography, Morison pouch, Morison’s pouch, ruptured ectopic pregnancy, free fluid, gestational sac, yolk sac, fetal pole, transducer, endometrium, intrauterine pregnancy, IUP, cul-de-sac
Physicians should consider the diagnosis of ectopic pregnancy in any woman in the first trimester of pregnancy who has abdominal or pelvic pain, vaginal bleeding, or both. Ectopic pregnancy is the most common cause of pregnancy-related death in the first trimester and accounts for about 10% of all pregnancy-related deaths. Missed ectopic pregnancy is a leading cause of emergency medicine malpractice claims. High-risk features for the possibility of ectopic pregnancy include history of ectopic pregnancy, history of pelvic inflammatory disease, use of an intrauterine device, and history of tubal surgery. Unfortunately, clinical findings alone cannot reliably diagnose or exclude ectopic pregnancy.1
Several studies have validated pelvic ultrasonography in the acute care setting, specifically in the emergency department, as diagnostically accurate and beneficial for flow.2, 3, 4 Bedside ultrasonography is an important tool for emergency medicine physicians and other acute care physicians to use in assessing patients’ risk for potential ectopic pregnancy. Early diagnosis can be very valuable in lessening morbidity and mortality. Diagnosis before tubal rupture can prevent life-threatening hemorrhage and increase the probability that the patient may be managed medically or via tube-conserving surgery. However, use of ultrasonographic imaging should never preclude adequate resuscitation or definitive surgical therapy in a patient who is hemodynamically unstable and in whom ectopic pregnancy is highly suspected.
The goal of bedside ultrasonography is to diagnose an intrauterine pregnancy (IUP). Ectopic pregnancy can be reliably excluded in patients with a demonstrated IUP, as heterotopic pregnancy remains very rare in patients who are not taking fertility agents. Heterotopic pregnancies occur in approximately 1 in 5,000 pregnancies, but the incidence increases to as high as 1 in 100 in women undergoing fertility stimulation or procedures. This limited ultrasound focus differs from the ultrasonography performed by the radiology department and has also been called point-of-care limited ultrasound (PLUS). When the serum level of beta human chorionic gonadotropin (β-HCG) is greater than 1500 mIU/mL, the level known as the discriminatory zone, transvaginal ultrasonographic findings of an IUP should be present.
Transverse picture of intrauterine pregnancy.
The first developmental structure big enough to be visualized by transvaginal ultrasonography is the gestational sac, which appears in the endometrial cavity at around 4.5-5 weeks’ gestation, which correlates to a β-HCG level of 1000-1500 mIU/mL. Measurement of the mean sac diameter (MSD) is important for estimating the gestational age as well as for sonographic confirmation of subsequent normal embryonic development.
A conservative definition of an ultrasound that is diagnostic for an IUP involves demonstration of a clearly defined yolk sac within the gestational sac.
Picture of gestational sac with yolk sac.
Transverse picture of gestational sac with yolk sac.
The yolk sac appears by 5-6 weeks’ gestation and should definitely be present when the MSD is greater than 8 mm. The embryo, or fetal pole, can be visualized on transvaginal ultrasonography by 6 weeks’ gestation and on transabdominal ultrasound by 7 weeks’ gestation, and it should be present when the MSD is greater than 16 mm. Embryonic cardiac activity starts to be visible at around 7 weeks’ gestation and should be visible if the crown-rump length, or fetal pole length, is greater than 5 mm.
Definitive ultrasonographic diagnosis of an ectopic pregnancy is made in only about 20% of cases, when an extrauterine pregnancy is clearly identified (ie, an extrauterine gestational sac with a yolk sac or fetal pole is visualized). There exist, however, numerous ultrasonographic findings that are highly suggestive of ectopic pregnancy, including an empty uterus in a patient with a β-HCG level above the discriminatory zone, an adnexal mass other than a simple cyst, echogenic fluid in the cul-de-sac, or anything more than a small amount of fluid in the cul-de-sac. Patients who exhibit such findings should be managed in consultation with an obstetrician; they likely will need surgical exploration or medical therapy with methotrexate.
Picture of uterus without a fetal pole and a complex adnexal mass consistent with ectopic pregnancy.
Ultrasonographic findings that are neither diagnostic nor highly suggestive of an IUP or ectopic pregnancy are classified as indeterminate. These findings include an empty uterus, an abnormal gestational sac (irregular border or MSD of a size where a secondary structure such as a yolk sac would be expected), a normal gestational sac without yolk sac or embryo, nonspecific intrauterine fluid collection, and ill-defined echogenic material within the endometrial cavity. Patients who exhibit these findings are generally monitored closely with serial β-HCG testing and clinical assessments, as about 10-25% of such patients have normal pregnancies.
Picture of abnormal endometrium in a patient with an ectopic pregnancy.
Bedside ultrasonography is indicated in the presence of vaginal bleeding or abdominal pain in a patient in the first trimester of pregnancy.
Do not perform bedside ultrasonography if it delays resuscitation or definitive surgical care in an unstable patient.
Anesthesia is generally not necessary for sonographic evaluation; however, patients may experience discomfort from the pressure of the transducer.
- Ultrasonograph with abdominal transducer, 3.5-5 MHz, and transvaginal transducer, 7.5-10 MHz
- Gloves
- Acoustic gel
- Transvaginal transducer probe cover
- Lubricating jelly (Because acoustic gel causes an intravaginal dermatitis, use the lubricating jelly Surgilube on the outside of the transducer cover.)
- For transabdominal ultrasonography, position the patient in the supine recumbent position.
- For transvaginal ultrasonography, position the patient in the supine lithotomy position.
- Explain the procedure, benefits, risks, and complications to the patient or the patient's representative. Ask the patient or the patient's representative if he or she would like others to be present for the procedure.
- The patient should be in a hospital gown, undressed from the waist down.
Transabdominal ultrasonography
- Transabdominal ultrasonography is best performed on a patient who has a full bladder.
- Expose the abdomen from xiphoid to pubis.
- Apply a generous amount of acoustic gel to the patient’s lower abdomen, the abdominal transducer, or both.
- The uterus is a muscular hollow organ behind the bladder and anterior to the colon, with a moderately echogenic, homogenous myometrium and a relatively hyperechoic endometrium.
- Scan the uterus in the transverse plane (hold the probe perpendicular to the patient’s long axis, with the indicator of the probe pointing toward the patient's right), sweeping from fundus to cervix.
Transverse probe placement for transabdominal obstetric examination.
- Scan the uterus in the sagittal plane (hold the probe parallel to the patient’s long axis, with the indicator of the probe pointing toward the patient's head), sweeping from side to side. Be sure to identify the landmarks: the bladder, the vaginal stripe, and the uterus.
Sagittal or longitudinal probe placement for transabdominal obstetric examination.
Sagittal viewing showing bladder, uterus (behind the bladder), and endometrial stripe (within the uterus).
- When scanning in the sagittal plane, assess for free fluid in the cul-de-sac, also known as the recto-uterine pouch or pouch of Douglas. A small amount of hypoechoic free fluid can be considered physiologic. Fluid tracking two thirds of the way up the posterior wall of the uterus is regarded as moderate. A larger amount of fluid, or fluid that tracks anteriorly and interposes between the uterus and the bladder, is considered large.5
- Apply acoustic gel to the patient’s right upper quadrant, scanning in the transverse and sagittal planes again to visualize the Morison pouch. Free fluid is generally not visualized until at least 500 mL of free fluid has accumulated; such accumulation is highly suggestive of ruptured ectopic pregnancy.7
Free fluid in the Morison pouch from a ruptured ectopic pregnancy.
Transvaginal ultrasonography
- Transvaginal ultrasonography is best performed on a patient who has an empty bladder.
- Position the patient in the supine lithotomy position, preferably on a stretcher equipped for pelvic exams (ie, with stirrups).
- Scan the uterus in both the long and short axis planes.6
- The cul-de-sac is formed by the peritoneal reflection anterior and posterior to the uterus. A small amount of anechoic fluid in the cul-de-sac is physiologic. Echogenic fluid in the cul-de-sac is highly suggestive of ruptured ectopic.
- Upon visualization of a round anechoic structure in the endometrial cavity that is consistent with a gestational sac, acquire pictures and measure the length, height, and width of the gestational sac to obtain the mean sac diameter. These measurements are taken from the inner aspects of the echogenic border of the sac. Visualization of a double decidual ring (ie, 2 echogenic rings around the gestational sac) is pathognomonic for an early IUP. In radiology literature, this is considered the earliest reliable sign of an IUP. Double decidual signs, however, are not consistently seen, and caution should be used in terms of using them to determine the presence or absence of an IUP. Prior to this stage, demonstration of a simple gestational sac is an indeterminate ultrasonographic finding.
- The yolk sac is a round echogenic ring with an anechoic center located within the gestational sac. The yolk sac can generally be used to determine the presence or absence of an IUP.
- The embryo is measured using crown-rump length, which is measured end-to-end (not including the yolk sac).
- An extraovarian adnexal echogenic ring (tubal ring sign), highly suggestive of an ectopic pregnancy, occurs when the fallopian tube develops a trophoblastic reaction to an ectopic gestational sac.
- Interstitial ectopic pregnancy is rare but has a higher mortality rate following rupture, as the area is richly vascular. An eccentrically located gestational sac with a thin or incomplete myometrial mantle around the sac is suggestive of an interstitial gestation; this is the interstitial line sign.
Technique pitfalls
- A pseudogestational sac can be confused with a genuine gestational sac.
- Intrauterine fluid is one of the most common ectopic findings misinterpreted as an early normal IUP.
- Failure to scan through the entire uterus, cervix, and adnexa can lead to missed ectopic pregnancies.
- Maintain a high level of suspicion for ectopic pregnancy as a cause of symptoms during the first trimester.
- To avoid missing ectopic pregnancies, scan systematically and widely, including the entire uterus and cervix in the transverse and sagittal planes.
- The primary role of emergency department obstetric ultrasonography is to demonstrate an IUP.
- When the β-HCG level is greater than 1500 mIU/mL, transvaginal ultrasonographic evidence of an IUP should exist. The first visible structure is the gestational sac. Subsequent yolk sac, embryo, and fetal cardiac activity should appear at predictable time intervals and mean sac diameter sizes.
- An extrauterine gestational sac with yolk sac or fetal pole is definitive evidence of an ectopic pregnancy. Other suggestive ultrasonographic findings include a complex adnexal mass, echogenic fluid in the cul-de-sac, a moderate to large amount of fluid in the cul-de-sac, and an empty uterus in a patient with a β-HCG level above the discriminatory zone.
- No major complications exist with performance of emergency department ultrasonography to evaluate first-trimester pregnancy.
- Sometimes, Doppler ultrasonography is used in early pregnancy evaluation to detect fetal cardiac activity or to better delineate adjacent vascular anatomy. The energy output of Doppler ultrasonography is substantially higher than conventional ultrasonography and may be harmful to the embryo.6
- Complications can ensue if an obstetrician is not consulted early in the treatment of a patient with early pregnancy and hemodynamic instability, acute abdomen, or falling hematocrit level.
| Media file 1:
Transverse probe placement for transabdominal obstetric examination. |
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Sagittal or longitudinal probe placement for transabdominal obstetric examination. |
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Sagittal viewing showing bladder, uterus (behind the bladder), and endometrial stripe (within the uterus). |
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Transverse picture of intrauterine pregnancy. |
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Transverse picture of gestational sac with yolk sac. |
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| Media file 7:
Picture of abnormal endometrium in a patient with an ectopic pregnancy. |
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| Media file 8:
Picture of uterus without a fetal pole and a complex adnexal mass consistent with ectopic pregnancy. |
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| Media file 9:
Free fluid in the Morison pouch from a ruptured ectopic pregnancy. |
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- Kaplan BC, Dart RG, Moskos M, et al. Ectopic pregnancy: prospective study with improved diagnostic accuracy. Ann Emerg Med. Jul 1996;28(1):10-7. [Medline].
- Shih CH. Effect of emergency physician-performed pelvic sonography on length of stay in the emergency department. Ann Emerg Med. Mar 1997;29(3):348-51; discussion 352. [Medline].
- 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. Mar 1996;27(3):283-9. [Medline].
- Durston WE, Carl ML, Guerra W, Eaton A, Ackerson LM. Ultrasound availability in the evaluation of ectopic pregnancy in the ED: comparison of quality and cost-effectiveness with different approaches. Am J Emerg Med. Jul 2000;18(4):408-17. [Medline].
- Dart R, McLean SA, Dart L. Isolated fluid in the cul-de-sac: how well does it predict ectopic pregnancy?. Am J Emerg Med. Jan 2002;20(1):1-4. [Medline].
- Dogra V, Paspulati RM, Bhatt S. First trimester bleeding evaluation. Ultrasound Q. Jun 2005;21(2):69-85; quiz 149-50, 153-4. [Medline].
- Rodgerson JD, Heegaard WG, Plummer D, Hicks J, Clinton J, Sterner S. Emergency department right upper quadrant ultrasound is associated with a reduced time to diagnosis and treatment of ruptured ectopic pregnancies. Acad Emerg Med. Apr 2001;8(4):331-6. [Medline].
Bedside Ultrasonography, First-Trimester Pregnancy excerpt Article Last Updated: Jan 8, 2008
Topic originally published: Jan 8, 2008
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