Transvaginal identification of the gestational sac occurs at approximately which HCG level?

• A. 100 mIU/mL
• B. 500 mIU/mL
• C. 1000 mIU/mL
• D. 1500 mIU/mL

Answer: (B)

Transvaginal identification of the gestational sac depends on the discriminatory hCG level, the point at which the early ultrasound can reliably visualize an intrauterine pregnancy with a high-resolution probe placed close to the uterus. In practice, the gestational sac becomes detectable with transvaginal ultrasound when hCG is about 1000 to 1500 mIU/mL. The transvaginal approach is more sensitive than transabdominal because the probe is nearer the gestational structures, allowing visualization sooner in early pregnancy. Values much lower than this (like 100 or 500) are typically below the detectability threshold, while around 1000 mIU/mL is the commonly cited benchmark. Some sources quote up to 1500 mIU/mL or slightly higher as the upper end of the discriminatory zone, but the key idea is that visualization is expected around the thousand-mark range.