At what level of 0-HCG, normal pregnancy can be earliest detected by TVS (Trans vaginal USG):
**Core Concept**
Normal pregnancy can be detected by transvaginal ultrasound (TVS) based on the presence of an intrauterine gestational sac, which is visualized when the beta-human chorionic gonadotropin (β-hCG) levels reach a certain threshold.
**Why the Correct Answer is Right**
The earliest detection of a normal pregnancy by TVS is possible when the β-hCG levels reach 1000-1500 IU/L. At this level, the sensitivity of the ultrasound is high enough to detect the gestational sac, which is a critical marker of early pregnancy. The presence of the gestational sac is associated with the formation of the yolk sac and the development of embryoblast and trophoblast, indicating a viable pregnancy.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because β-hCG levels of 500 IU/L are too low for reliable detection of the gestational sac by TVS.
**Option B:** This option is incorrect because β-hCG levels of 2000 IU/L are higher than the threshold for early detection, and the gestational sac may already be visible at lower levels.
**Option C:** This option is incorrect because β-hCG levels of 800 IU/L are below the threshold for reliable detection of the gestational sac by TVS.
**Clinical Pearl / High-Yield Fact**
A key point to remember is that the presence of a yolk sac and embryoblast within the gestational sac is crucial for confirming a viable intrauterine pregnancy.
**Correct Answer: C. 1000-1500 IU/L**