Focus On - Ultrasound Imaging in First Trimester Pregnancy // ACEP
After reading this article, the physician should be able to: Perform a transvaginal ultrasound on a patient in the first trimester of pregnancy. Perform a transvaginal ultrasound on a patient in the first trimester of pregnancy. Identify several different pathologic processes that may be encountered during evaluation of the adnexa.
Ultrasound has emerged as the gold standard imaging modality for patients presenting to the emergency department in the first trimester with pregnancy-related complaints.1
It has become increasingly important for the emergency physician to be able to use bedside ultrasound to identify the conditions that require emergent gynecological consultation, because the availability of ultrasound through the radiology department may be limited. In a time-efficient manner, focused pelvic ultrasound may be performed at the same time as the pelvic examination.
The primary question of interest is, "Is the conceptus inside the uterus?" Evaluation for heterotopic and molar pregnancy, miscarriage, ovarian cysts, and pelvic inflammatory disease with tubo-ovarian abscess will also be briefly addressed in this article. How to Perform Transvaginal Ultrasound
An endocavitary probe is covered with a glove after transmission gel is first placed into one of the fingers, or a prefabricated sheath designed for this purpose may be used (see photo 1). A sterile gel, such as Surgilube, should be placed as a transmission medium external to the sheath, as this will be placed into the vagina. The patient should be given the opportunity to void. A full bladder during the examination will retrovert the uterus and can be uncomfortable for the patient.
With the patient placed in the lithotomy position, insert the probe into the vagina with the probe marker up, allowing a view of the uterus longitudinally (see photo 2). The bladder is seen on the left of the display screen, the body of the uterus in the middle and the cervix on the right. The vagina is not visualized because the probe is within it. The depth should be adjusted to fit the uterus on the screen and to visualize the posterior cul-de-sac.
Fan the probe to the right and to the left to scan through the body of the uterus and to assess that any gestation is contained within the uterus and not lying outside of it.
Assess for free fluid posterior to the uterus, as this may indicate a pathological process. Fluid is easily seen in this location, and ultrasound has replaced culdocentesis as the standard method for detecting free fluid (see photo 3).2
The probe should then be rotated 90 degrees counterclockwise, placing the probe marker to the patient's right. This is the uterus viewed in the coronal plane (see photo 4). Adjust depth to fit the entire uterus on the screen, and evaluate the posterior cul-de-sac. The uterus should be scanned through in its entirety in this plane as well, by gently moving the tip of the probe up and down.
Evaluation of the adnexa is challenging, especially for a novice sonographer. There are a few tricks that can be used to facilitate finding the ovaries.
First, while visualizing the uterus in the coronal plan, scan up toward the uterine fundus. Move the probe in a plane parallel to this level toward the lateral fornix of each side. Following the cornua laterally to the adnexa will bring the fallopian tube and ovary into view. Another method is to move the probe laterally to find the iliac vessels. The ovary lies just medial and anterior (toward the patient's abdomen) of these vessels, and angling the probe in this way should bring each into view.
Transabdominal ultrasound also can be used to evaluate first-trimester pregnancy, with a few differences.
First, because the probe is farther away from the desired structures, 7 weeks from the last menstrual period (LMP) must elapse before the gestation can be visualized. Second, using the transabdominal probe, the bladder is seen on the right of the screen with the vagina seen just behind it (see photo 5). Third, unless there is significant pathology enlarging them, the ovaries are difficult to visualize. Principles of scanning otherwise remain the same--visualize the uterus in both longitudinal and transverse planes, and adjust depth to fit the entire uterus on the screen to evaluate the posterior cul-de-sac. Ultrasound Findings
Gestational dating by LMP can be unreliable,3 and because ectopic pregnancies develop abnormally, a surgically significant ectopic can be present at low serum levels of ß-hCG. An ultrasound should always be performed.
At approximately 5-6 weeks gestation, corresponding to a ß-hCG of 1,500-2,000 mIU/mL, the gestational sac is first visualized using transvaginal ultrasound. The intra-uterine pseudo-sac of an ectopic pregnancy can be confused with the gestational sac. Therefore, it is prudent to make the diagnosis of intrauterine pregnancy only when a yolk sac is seen (see photo 6).
A yolk sac is seen at approximately 6 weeks after the LMP. At approximately 7 weeks after the LMP, a fetal pole can be visualized (see photo 7), and approximately 8 weeks after the LMP, the fetal heartbeat can be seen.
An interstitial ectopic pregnancy is a rare occurrence, but it is a clinically significant presentation with which the emergency physician should be familiar.
Pathophysiologically, the gestation implants at the junction of the fallopian tube and the uterus. These pregnancies progress into the second trimester because the myometrium is thick enough to allow for considerable growth (up to 13-15 weeks gestation) before rupture may occur. A well-invested blood supply develops, and the results of rupture can be catastrophic.
This diagnosis should be considered if the gestation is not centrally located, with only a thin myometrial layer surrounding it. The myometrial mantle should be measured at the thinnest part of the uterus (see photo 6), and a thickness of less than 5-7 mm is suspicious for interstitial ectopic pregnancy.1 In these cases, obstetrical consultation is advised.
Complete hydatidiform moles develop from an aberrant fertilization event that leads to the development of an abnormal proliferative process. Patients may have theca lutein cysts, hyperemesis gravidarum, and pre-eclampsia prior to 20 weeks gestation caused by abnormally high levels of ß-hCG. Sonographically, the uterus is filled with a heterogeneous mass with "grapelike" appearance, and a fetus is notably absent (see photo 8). Miscarriage
Threatened or complete miscarriage is a common presentation in the emergency department. During their pregnancies, 20%-25% of pregnant patients will experience some bleeding.5 All scenarios require confirmation that the gestation is intrauterine. Previous sonographic documentation of an intrauterine pregnancy should be confirmed. Visualization of an intrauterine gestation after 8-9 weeks gestation should show evidence of a fetal heartbeat. Lack of fetal heart motion at this stage is concerning for intrauterine fetal demise. In these situations, the case should be managed with gynecologic consultation. Adnexal Evaluation
Etiology of adnexal masses encountered during pregnancy includes ectopic pregnancy, ovarian cysts, and tubo-ovarian abscess.
Ectopic pregnancy: The incidence of ectopic pregnancy in women presenting to the emergency department with vaginal bleeding or pain in the first trimester has been estimated at approximately 10%, 6,7 and it remains the leading cause of maternal death in the first trimester.8
The increasing incidence of ectopic pregnancy is caused by a number of factors, including treatments for infertility, pelvic inflammatory disease, tubal surgery, and the use of intrauterine devices. Most (95%) ectopic pregnancies occur in the fallopian tube,9 and ultrasound evaluation may reveal an adnexal mass external to the uterus with a yolk sac or fetus (see photo 9).
Independent movement of the mass and ovary when gently probed with the ultrasound transducer is highly suggestive of ectopic pregnancy, and can differentiate it from an ovarian cyst.10 The posterior cul-de-sac should be evaluated for fluid. The hepatorenal recess may contain fluid as well, if significant hemorrhage is present. It is prudent to evaluate this area in cases where intra-uterine pregnancy cannot be confirmed.
Heterotopic pregnancies, or the presence of more than one gestation (one intrauterine and the other extrauterine), are historically rare, but have increased in frequency up to 1 in 100 in patients undergoing assisted reproductive techniques.11 In these high-risk patients, careful evaluation of the adnexa should take place despite the presence of an intrauterine pregnancy, and obstetric/gynecologic consultation is advised.
Ovarian cysts: Most ovarian cysts in pregnancy are corpus luteum cysts, physiologic remnants of the mature follicle after ovulation. They are thin walled and hypo-echoic, range from 3 cm to 11 cm in diameter, and usually occur in patients with high levels of ß-hCG, such as patients with molar pregnancy or those receiving treatment for infertility with exogenous hormone administration.12 Pain may be caused by hemorrhage into the cyst, which appears as internal echoes, or by cyst rupture, which may appear as free fluid in the posterior cul-de-sac or surrounding the ovary.
Pelvic inflammatory disease (PID): PID and tubo-ovarian abscess are rare in pregnancy. Ultrasound has been found to be 93% sensitive and 98% specific in the diagnosis of tubo-ovarian abscess. It is the safest way to evaluate a pregnant patient.13 Findings on ultrasound can include a complex adnexal mass, often difficult to discern from surrounding structures because of inflammation (see photo 10).
Ovarian cysts and tubo-ovarian abscess are only a small subset of possible ovarian pathology, and processes enlarging the adnexa can make it prone to torsion. Evidence of ovarian pathology should prompt gynecologic consultation. Summary
Focused pelvic ultrasound should be used in the emergency department to evaluate patients in the first trimester of pregnancy presenting with pregnancy-related complaints. It can be done at the time of the pelvic examination, and it can quickly identify conditions that require emergent surgical consultation. Resources American College of Emergency Physicians. Emergency Ultrasound Imaging Criteria Compendium. Annals of Emergency Medicine. 2006; 48:487-510. Katz: Comprehensive Gynecology, 5th ed. Philadelphia: Mosby, 2007. Geirsson R.T., Busby-Earle R.M. Certain dates may not provide a reliable estimate of gestational age. British Journal of Obstetrics and Gynecology. 1991;98:108-9. Adapted from Dart R.G., Role of pelvic ultrasonography in evaluation of symptomatic first-trimester pregnancy. Annals of Emergency Medicine. 1999;33:310-20. Marx: Rosen's Emergency Medicine: Concepts and Clinical Practice, 6th ed. Philadelphia: Mosby Elsevier, 2006. Kaplan B.C., et al. Ectopic pregnancy: Prospective study with improved diagnostic accuracy. Annals of Emergency Medicine. 1996;28:10. Barnhart K.T., et al. Diagnostic accuracy of ultrasound above and below the ß-hCG discriminatory zone. Obstetrics and Gynecology. 1999;94:583. Centers for Disease Control. Current trends in ectopic pregnancy: United States, 1990-02. Morbidity and Mortality Weekly Report. 1995;44:46-8. Webb, E.M., Green, G.E., Scoutt, L.M. Adnexal mass with pelvic pain. Radiology Clinics of North America. 42; March 2004. Blaivas M. Reliability of adnexal mass mobility in distinguishing possible ectopic pregnancy from corpus luteum cysts. Journal of Ultrasound Medicine. 2005;24:599-603. Tal, J. et al. Heterotopic pregnancy after ovulation induction and assisted reproductive technologies: a literature review from 1971 to 1993. Fertility and Sterility 1996;66:1-12. Purcell, K. and Wheeler, J.E. "Benign disorders of the ovaries and oviducts." Current Obstetric and Gynecologic Diagnosis and Treatment. Ed. A. DeCerney and L. Nathan. New York: McGraw-Hill, 2003. Zeger W., Holt, K. Gynecologic Infections. Emergency Medicine Clinics of North America. 2003;21:631-48. Contributors
Dr. Saul is a fellow in the ultrasound division, department of emergency medicine at St. Luke's-Roosevelt Hospital Center in New York City. Dr. Lewiss is director of the ultrasound division, department of emergency medicine at St. Luke's-Roosevelt Hospital Center. Medical Editor Dr. Robert C. Solomon is an attending emergency physician at Trinity Health System in Steubenville, Ohio, and clinical assistant professor of emergency medicine at the West Virginia School of Osteopathic Medicine. Disclosures
In accordance with the Accreditation Council for Continuing Medical Education (ACCME) Standards and American College of Emergency Physicians policy, contributors and editors must disclose to the program audience the existence of significant financial interests in or relationships with manufacturers of commercial products that might have a direct interest in the subject matter.
Dr. Saul, Dr. Lewiss, and Dr. Solomon have disclosed that they have no significant relationships with or financial interests in any commercial companies that pertain to this educational activity.
"Focus On: Ultrasound Imaging in First Trimester Pregnancy" has been planned and implemented in accordance with the Essential Areas and Policies of the Accreditation Council for Continuing Medical Education (ACCME).
ACEP is accredited by the ACCME to provide continuing medical education for physicians. ACEP designates this educational activity for a maximum of one Category 1 credit toward the AMA Physician's Recognition Award. Each physician should claim only those credits that he or she actually spent in the educational activity. "Focus On: Ultrasound Imaging in First Trimester Pregnancy" is approved by ACEP for one ACEP Category 1 credit. Disclaimer
ACEP makes every effort to ensure that contributors to College-sponsored programs are knowledgeable authorities in their fields. Participants are nevertheless advised that the statements and opinions expressed in this article are provided as guidelines and should not be construed as College policy. The material contained herein is not intended to establish policy, procedure, or a standard of care. The views expressed in this article are those of the contributors and not necessarily the opinion or recommendation of ACEP. The College disclaims any liability or responsibility for the consequences of any actions taken in reliance on those statements or opinions.
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