UCONN Emergency Medicine Interest Group

Journal Article Synopsis: β-hCG, Ultrasound, and Ectopic Pregnancies

In JOURNAL CLUB on August 8, 2011 at 3:32 PM

Summary of “Use of a β-hCG Discriminatory Zone With Bedside Pelvic Ultrasonography” By Ralph Wang et al, Annals of Emergency Medicine vol 58: pp. 12-20. 2011.

What is already known on this topic:
Currently, pregnant women presenting to the ED with abdominal pain, vaginal bleeding, or syncope are assessed with pelvic ultrasonography and quantitative serum β-human chorionic gonadotropin (β-hCG) to rule out the possibility of an ectopic pregnancy. In 10-30% of these cases pelvic ultrasound is unable to reveal either an intrauterine (IUP) or ectopic pregnancy- an “indeterminate result”. A level of β-hCG above the “discriminatory zone” of 1500-3000 mIU/mL, in combination with an indeterminate ultrasound, has been shown to be associated with ectopic pregnancy.

What question this study addressed:
What is the utility of the β-hCG discriminatory zone in differentiating between ectopic and intrauterine pregnancies after an indeterminate bedside pelvic ultrasonography in symptomatic pregnant patients presenting to the ED?

What was the study design:
Cross-sectional study of 256 first-trimester pregnant patients presenting to ED with symptoms of abdominal pain or vaginal bleeding. All pelvic ultrasonography was performed by emergency physicians who were blinded to the patient’s β-hCG levels. Research assistants (blinded to the ultrasound results) contacted and performed a standardized interview with all enrolled patients at 8 weeks.

What this study adds to our knowledge:
A β-hCG cutoff of 3000 mIU/mL is not acceptable for use in clinical practice when attempting to identify ectopic pregnancy in symptomatic patients with an indeterminate result on bedside pelvic ultrasonography (sensitivity of 35% and specificity of 58%). On follow up, it was found that 65% of patients with an ectopic pregnancy have a β-hCG < 3000 mIU/mL.

How this is relevant to clinical practice:
When pelvic ultrasound is indeterminate for intrauterine pregnancy, serum β-hCG level alone does not differentiate intrauterine and ectopic pregnancy. A β-hCG cutoff of 3,000 mIU/mL will not aid with the exclusion of ectopic pregnancy and will cause 65% of cases to be missed.

Other considerations:
In the future the discriminatory zone of β-hCG must be re-evaluated. The bedside pelvic ultrasound can reliably exclude ectopic pregnancy only when they demonstrate a clear intrauterine pregnancy in symptomatic pregnant ED patients. Practitioners should avoid an inappropriate interpretation of β-hCG levels in patients without a clear diagnostic result.

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