## **Core Concept**
The establishment of fetoplacental circulation is a critical process in early pregnancy, involving the development of blood vessels within the placenta and the umbilical cord. This process ensures the exchange of oxygen, nutrients, and waste products between the mother and the fetus. The fetoplacental circulation becomes functional as the embryo's cardiovascular system matures.

## **Why the Correct Answer is Right**
The correct answer, **8 weeks**, is the period when the fetoplacental circulation is well established. By around 8 weeks of gestation, the primitive heart tube has developed into a four-chambered heart, and the major blood vessels have formed. The umbilical arteries and vein, which are crucial for fetoplacental circulation, start to develop early in embryonic life. The umbilical vein carries oxygenated blood from the placenta to the fetus, while the umbilical arteries carry deoxygenated blood from the fetus to the placenta. This circulation is essential for the growth and development of the fetus.

## **Why Each Wrong Option is Incorrect**
- **Option A: 6 weeks** - While the beginnings of the cardiovascular system and the formation of the umbilical vessels start around this period, the fetoplacental circulation is not fully established.
- **Option B: 10 weeks** - Although the fetoplacental circulation is functional and refining at this point, saying it is established by 10 weeks might be slightly late, as it becomes functional a bit earlier.
- **Option D: 12 weeks** - This is too late for the initial establishment of fetoplacental circulation; by 12 weeks, the circulation is well-functioning, but it was established earlier.

## **Clinical Pearl / High-Yield Fact**
A key point to remember is that the establishment of fetoplacental circulation is an early event in embryonic development, critical for the subsequent growth of the fetus. Clinically, disturbances in this circulation can lead to complications such as intrauterine growth restriction (IUGR).

## **Correct Answer: C. 8 weeks**