Again these terms are important to the emergency

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Again, these terms are important to the emergency physician only in terms of clear communication. The purpose of performing bedside emergency first trimester ultrasound is to diagnose an intrauterine pregnancy in patients with an acceptably low risk of heterotopic pregnancy (non-IVF, no history of ectopic pregnancy) so they can be discharged and followed up as out- patients safely. If an intrauterine pregnancy is not diagnosed, most emer- gency department patients should be referred for formal sonography and gynecology consultation. hCG levels Another area of much confusion and debate is the correlation of serum human chorionic gonadotropin (hCG) levels with ultrasound findings. The first important rule for the emergency physician is that there is no hCG level at which a patient can be ruled out for ectopic pregnancy. Ectopic pregnancies have been described with levels < 30 IU/mL, and very fre- quently < 1000 IU/mL [ 8,9 ]. Therefore, pelvic sonography should be done for any patient who is pregnant regardless of beta-hCG [ 8 –10]. The concept of a discriminatory zone becomes more significant after pelvic sonography is complete. The discriminatory zone is the level of beta-hCG at which an intrauterine pregnancy should be seen 100% of the time. Transvaginal ultrasound is able to visualize intrauterine pregnancies earlier, and the discriminatory zone is usually accepted as 1500 IU/mL. The discrimin- atory zone for transabdominal ultrasound is usually believed to be between 4000 and 6500 IU/mL because it uses a lower-frequency probe and thus images with less resolution [11 ]. Therefore, if an ultrasound is indeterminate and the serum hCG is above the discriminatory zone, the suspicion for ectopic pregnancy should be increased [ 12 ]. However, serum quantitative hCG levels are mostly helpful in following a patient over time, and there is no level at which a patient will not require an ultrasound (except zero). Anatomy There are several anatomic relationships that can help guide the sonographic evaluation of the female pelvis ( Figure 4.1 ). The bladder is anterior to the Diagnostic ultrasound 93 First trimester ultrasound
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uterus unless it is empty, when the anteverted uterus can fold over an under- filled bladder. The ovaries are usually found at the end of the fallopian tubes and are anterior and medial to the iliac vessels ( Figure 4.2 ). If the bladder is full, it is a good acoustic window for visualizing the uterus transabdominally. However, it is easier to visualize the uterus transvaginally with an empty bladder because then the uterus will be anteflexed in most cases over the vaginal introitus. Technique There are two approaches to performing the sonographic exam of an early pregnancy: transabdominal and transvaginal. Usually, a transabdominal scan is done first while the patient still has a full bladder. The patient then can empty her bladder prior to the transvaginal scan if the transabdominal scan was non-diagnostic for intrauterine pregnancy. In patients with unclear gestational age, it is even more important to perform an abdominal scan first.
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