UMEM Educational Pearls

Ectopic pregnancy ranges from 3 to 13% in symptomatic first-trimester ED patients. 

The discriminatory zone is defined as the level of Bhcg above which an intrauterine pregnancy can be reliably detected using ultrasound.  (1,500 mIU/mL for transvaginal ultrasound and 3,000 mIU/mL for transabdominal ultrasound)

One study found that an intrauterine pregnancy was visualized with as low as 1,440 mIU/mL and patients with an interdeterminate pelvic ultrasound who were found to have an ectopic pregnancy had a Bhcg greater than 3,000 mIU/mL only 35% of the time. 


Bottom Line: If you have a symptomatic patient with an empty uterus and a bhcg above the discriminatory zone, they have a higher risk for ectopic pregnancy. However, if your patient is symptomatic, they should still have further evaluation for ectopic pregnancy even if they have a bhcg lower than the discriminatory zone. 


Wang R, Reynolds TA, West HH, Ravikumar D, Martinez C, McAlpine I, Jacoby VL, Stein JC. Use of a β-hCG discriminatory zone with bedside pelvic ultrasonography. Ann Emerg Med. 2011 Jul;58(1):12-20. doi: 10.1016/j.annemergmed.2010.12.023. Epub 2011 Feb 18. PMID: 21310509.