A woman presents with 6 weeks of amenorrhea, beta-hCG 2400 mIU/mL, and transvaginal ultrasound showing no intrauterine pregnancy but a 2.5 cm adnexal mass with complex echogenicity and no fetal heartbeat. She is hemodynamically stable. What is the beta-hCG threshold (discriminatory zone) above which a normal intrauterine pregnancy should be visible on TVUS?

• A 1500–2000 mIU/mL ✓
• B 500 mIU/mL
• C 1000 mIU/mL
• D 3500–5000 mIU/mL

Explanation

The discriminatory zone for transvaginal ultrasound (TVUS) is 1500–2000 mIU/mL (per ACOG/RCOG): at beta-hCG levels above this threshold, a normal intrauterine pregnancy (IUP) should be visible as a gestational sac with TVUS. Absence of IUP above the discriminatory zone strongly suggests ectopic pregnancy, failed IUP (miscarriage), or rarely multifetal pregnancy. At 2400 mIU/mL with no IUP on TVUS, ectopic pregnancy must be managed — in this stable patient, methotrexate is appropriate if criteria are met (adnexal mass < 3.5 cm, no fetal cardiac activity, tube unruptured).

Reference: Williams Obstetrics, 26th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.