Elevated HCG with an Empty Uterus Does Not Always Mean Ectopic Pregnancy
Live birth can occur in women with elevated HCG and no gestational sac seen on initial transvaginal ultrasound.
Until recently, common teaching was that when serum β human chorionic gonadotropin (β-HCG) is >1000–2000 mIU/mL — the "discriminatory zone" — a gestational sac should be seen on transvaginal ultrasound in normal intrauterine pregnancy. To test this, researchers at a Boston hospital analyzed data for 202 patients during an 11-year period who had elevated β-HCG on the same day as transvaginal ultrasound showing no intrauterine fluid collection and then had subsequent ultrasound evidence of a live intrauterine embryo or fetus.
On the day of initial scan, β-HCG levels were <1000 mIU/mL in 80% of patients, 1000–1499 in 9%, 1500–1999 in 6%, and >2000 mIU/mL in 5%. None of the 9 patients with β-HCG levels >2000 mIU/mL had fibroids or other anatomic abnormalities that would have interfered with visualization of intrauterine fluid collection. The highest initial β-HCG level in a pregnancy that culminated in a live birth was 4336 mIU/mL. Initial β-HCG levels were not associated with pregnancy outcomes.
Comment: The Society of Radiologists in Ultrasound is planning a consensus conference on early first trimester sonography in 2012, which might well end the notion of the HCG "discriminatory zone" for diagnosis of ectopic pregnancy. Nevertheless, in hemodynamically stable patients with elevated β-HCG and no gestational sac or adnexal masses suggestive of ectopic pregnancy on transvaginal ultrasound, serial β-HCG measurement and repeat ultrasound to assess for a viable fetus is a reasonable option before diagnosing ectopic pregnancy.
Published in Journal Watch Emergency Medicine December 16, 2011
Doubilet PM and Benson CB. Further evidence against the reliability of the human chorionic gonadotropin discriminatory level. J Ultrasound Med 2011 Dec; 30:1637.
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