A 29-year-old woman with 7 weeks amenorrhoea and positive urine pregnancy test has a transvaginal scan showing no intrauterine gestational sac and no definite adnexal mass. Serum beta-hCG is 1200 mIU/mL. What is the most appropriate interpretation?
- A This is below the discriminatory zone, so the finding is indeterminate and repeat beta-hCG in 48 hours is advised ✓
- B Ectopic pregnancy is confirmed and methotrexate should be given
- C Early intrauterine pregnancy too small to visualise
- D Pseudogestational sac of ectopic pregnancy
Correct answer: A. This is below the discriminatory zone, so the finding is indeterminate and repeat beta-hCG in 48 hours is advised
Explanation
With transvaginal scanning, the discriminatory level of serum beta-hCG above which an intrauterine gestational sac should reliably be visible is approximately 1500 to 2000 mIU/mL. At 1200 mIU/mL the study is indeterminate, so serial quantitative beta-hCG after 48 hours is appropriate. Giving methotrexate risks treating a viable early intrauterine pregnancy, while calling it ectopic is unjustified before crossing the discriminatory zone.
Reference: Callen's Ultrasonography in Obstetrics and Gynecology, 6th ed.
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Written and medically reviewed by the StethoPrep medical team.