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The Speed of Sound

The Speed of Sound

The Discriminatory Zone's 15 Minutes is Over

Butts, Christine MD

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doi: 10.1097/01.EEM.0000480785.00502.92

    Who doesn't love looking at ultrasounds of babies? Even in the midst of an insane shift in our ED, I love to take a moment to reassure an anxious patient (and myself, at times) by showing her an ultrasound of her fetus moving around normally. Not to mention, it's fun to watch.

    But we often see patients with early pregnancies who present with bleeding or cramping and no obvious intrauterine pregnancy (IUP) on our ultrasound or radiology's. The use of the beta-human chorionic gonadotropin (β-hcg) level heavily guided the management of these patients in the past. The level of this hormone was presumed to correlate reliably to the progress of the pregnancy, and the term discriminatory zone was used to describe the level above which evidence of an intrauterine pregnancy could be expected to be seen (most often between 1000 to 2000 mIU per milliliter). The numerical level tended to fluctuate depending on the source, but this concept was prevalent in the literature as recently as 2014, and many who trained in the decades before that frequently use this concept in their practice.

    A shift in how the β-hcg level should be used in the absence of an IUP has occurred over the past few years, however. Rumblings started in the literature in the early 2000s and gained momentum as case reports came to light of birth defects and miscarriages resulting from methotrexate use in cases of mistakenly presumed ectopic pregnancy. An extensive review was published in the New England Journal of Medicine based on a literature review by experts in obstetrics, radiology, and emergency medicine. (2013;369[15]:1443.)

    This study was well publicized, but the concept of the discriminatory zone stubbornly hangs on; it still appears in recent textbooks.

    The article's authors essentially argue for avoiding the use of a single β-hcg level in clinical decision-making in stable patients. To put it simply, they suggest scrapping the discriminatory zone altogether. How should we use the β-hcg when the ultrasound is nondiagnostic? If the level is greater than 2000, there is still a good chance that the pregnancy will progress. Watchful waiting and serial β-hcg measurements are advised, provided the patient is stable and the ultrasound is otherwise not concerning (absence of significant free fluid or adnexal abnormalities). If the level is greater than 3000, the chance of nonviable pregnancy increases significantly, but a viable pregnancy still cannot be ruled out. These patients should also be monitored with serial blood testing and ultrasound.

    Decreasing the importance of a single β-hcg measurement in the analysis of early pregnancy is not really a controversial topic, but may represent a bit of a paradigm shift for many EPs (and other physicians as well). The discriminatory zone is a concept that is well established, but its time appears to have come and gone.

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