**Core Concept**
The weight of the placenta at term is an essential parameter in obstetric ultrasound and is used to assess fetal growth and development. The normal weight of a placenta at term is approximately 470-600 grams, which is roughly 10-15% of the fetal birth weight.

**Why the Correct Answer is Right**
The placenta grows in sync with the fetus and reaches its maximum weight by the 38th week of gestation. The placental weight is determined by the fetal demand for oxygen and nutrients, which is influenced by factors such as fetal growth rate, maternal nutrition, and placental efficiency. The placenta's weight is also a reflection of its functional capacity, with a well-nourished placenta being essential for fetal growth and development.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because the placental weight at term is not typically less than 300 grams. A placenta weighing less than 300 grams may indicate placental insufficiency or fetal growth restriction.
* **Option B:** This option is incorrect because the placental weight at term is not typically more than 800 grams. A placenta weighing more than 800 grams may indicate placental hypertrophy or fetal macrosomia.
* **Option C:** This option is incorrect because the placental weight at term is not typically the same as the fetal birth weight. The placental weight is usually around 10-15% of the fetal birth weight.

**Clinical Pearl / High-Yield Fact**
A placenta weighing less than 300 grams or more than 600 grams is considered abnormal and may be associated with adverse pregnancy outcomes.

**Correct Answer: D. 470-600 grams.**