Gestational sac is seen on TVS as early as :
**Core Concept**
The transvaginal ultrasound (TVS) is a sensitive imaging modality for detecting early pregnancy-related structures, including the gestational sac. The gestational sac is an early sign of pregnancy, and its visualization is crucial for confirming intrauterine pregnancy.
**Why the Correct Answer is Right**
The gestational sac is typically visible on TVS as early as 4.5-5 weeks of gestation. This is because TVS allows for higher resolution imaging of the uterus and its contents compared to transabdominal ultrasound (TAUS). The gestational sac is visualized as an anechoic or hypoechoic structure within the endometrial cavity, surrounded by a hyperechoic ring representing the yolk sac. The visualization of the gestational sac on TVS is facilitated by the proximity of the ultrasound probe to the uterus, which reduces the amount of intervening tissue and allows for clearer imaging.
**Why Each Wrong Option is Incorrect**
**Option A:** This is too early for the gestational sac to be visualized on TVS, as it is typically not detectable before 4.5-5 weeks of gestation.
**Option B:** This is inconsistent with the current understanding of gestational sac visualization on TVS, which is typically possible before 6 weeks of gestation.
**Clinical Pearl / High-Yield Fact**
It is essential to remember that the visualization of the gestational sac on TVS is a critical step in confirming intrauterine pregnancy and ruling out ectopic pregnancy. A non-visualized gestational sac on TVS at 6-7 weeks of gestation raises suspicion for an ectopic pregnancy and warrants further evaluation.
**Correct Answer: C. 4.5-5 weeks**