**Core Concept**
Passive diffusion is the primary mechanism by which certain drugs are transferred across the placenta from the mother to the fetus. However, some lipophilic drugs can also be actively transported across the placental barrier by facilitated diffusion, a process mediated by the placental enzyme P-glycoprotein.

**Why the Correct Answer is Right**
The correct answer is due to its ability to undergo enterohepatic recirculation, which allows it to accumulate in the fetus. Enterohepatic recirculation is a process by which a drug is secreted into the bile, reabsorbed from the intestine, and then returned to the bloodstream, increasing its plasma concentration. This process is particularly relevant for lipophilic drugs like the correct answer, which can easily cross the placental barrier and accumulate in the fetus.

**Why Each Wrong Option is Incorrect**
* **Option A:** This drug is primarily excreted by the kidneys and does not undergo significant enterohepatic recirculation, making it less likely to accumulate in the fetus.
* **Option B:** Although this drug is lipophilic, it is primarily metabolized by the liver and does not undergo significant enterohepatic recirculation, limiting its accumulation in the fetus.
* **Option D:** This drug is primarily excreted in the urine and does not undergo significant enterohepatic recirculation, making it an unlikely candidate for significant accumulation in the fetus.

**Clinical Pearl / High-Yield Fact**
When prescribing medications to pregnant women, it is essential to consider the potential for accumulation in the fetus and the role of enterohepatic recirculation in this process.

**Correct Answer:** C. Digoxin