**Core Concept**
Fetal cardiac pulsation can be detected by ultrasound (USG) as early as 5-6 weeks of gestation, marking the beginning of fetal development. This is made possible by advances in ultrasound technology, which enable the detection of even the smallest fetal movements. The detection of fetal cardiac pulsation is crucial for assessing fetal well-being and monitoring fetal growth throughout pregnancy.

**Why the Correct Answer is Right**
The correct answer is **B. 5-6 weeks**. This is because the fetal heart starts beating around 5-6 weeks of gestation, and as the embryo grows, the heart becomes more visible on ultrasound. The fetal heart rate is approximately 100-160 beats per minute, and the cardiac pulsation can be detected using high-frequency ultrasound transducers. The detection of fetal cardiac pulsation is an essential milestone in fetal development, and it allows for the assessment of fetal well-being and growth throughout pregnancy.

**Why Each Wrong Option is Incorrect**
* **Option A:** 8-10 weeks - This is too late for the earliest detection of fetal cardiac pulsation.
* **Option C:** 3-4 weeks - Fetal cardiac pulsation is not detectable at this early stage of gestation.
* **Option D:** 11-12 weeks - This is still too late for the earliest detection of fetal cardiac pulsation.

**Clinical Pearl / High-Yield Fact**
It is essential to note that the detection of fetal cardiac pulsation is not a guarantee of fetal viability, and other factors such as fetal growth restriction, chromosomal abnormalities, and maternal health conditions must be considered in conjunction with fetal cardiac pulsation for accurate assessment of fetal well-being.

**Correct Answer: B. 5-6 weeks**