Gestation sac is picked up by USG earliest at
**Core Concept**
The gestation sac is a critical structure in early pregnancy, and its detection is essential for confirming fetal viability. The gestation sac is a fluid-filled structure that forms around the implanted blastocyst, which contains the developing embryo.
**Why the Correct Answer is Right**
The gestation sac is typically visible on ultrasound (USG) around 4.5-5 weeks of gestation, when the embryo is approximately 5-6 mm in size. This is because the gestation sac is large enough to be detected by ultrasound at this stage, and it is also visible because it is filled with clear fluid, making it more conspicuous on the ultrasound image. The detection of the gestation sac is an important milestone in early pregnancy, as it helps to confirm fetal viability and rule out ectopic pregnancy.
**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because it is too early for the gestation sac to be visible on USG. At this stage, the embryo is still too small to be detected by ultrasound.
* **Option B:** This option is incorrect because it is too late for the gestation sac to be visible on USG. At this stage, the embryo has already developed into a more advanced stage, and the gestation sac may not be as prominent.
* **Option D:** This option is incorrect because it is not a commonly used time frame for detecting the gestation sac on USG.
**Clinical Pearl / High-Yield Fact**
It is essential to note that the detection of the gestation sac on USG is not always a guarantee of fetal viability. Other factors, such as fetal cardiac activity and embryonic development, should also be assessed to confirm fetal viability.
**Correct Answer:** C. 5 weeks