**Core Concept**
The oxygen saturation of blood in the umbilical artery is an indicator of placental function and fetal well-being. It reflects the balance between oxygen delivery from the maternal circulation and oxygen consumption by the fetus. The umbilical artery carries deoxygenated blood from the fetus to the placenta.

**Why the Correct Answer is Right**
The oxygen saturation of blood in the umbilical artery is typically around 30-40%. This is because the umbilical artery carries deoxygenated blood from the fetus to the placenta, where it picks up oxygen and nutrients. The low oxygen saturation in the umbilical artery is a result of the high oxygen extraction by the fetal tissues and the limited capacity of the placenta to deliver oxygen to the fetus. The oxygen saturation in the umbilical artery is often used as an indicator of fetal distress or placental insufficiency.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because the oxygen saturation in the umbilical artery is not around 70-80%, which is the typical range for oxygen saturation in the peripheral arteries of adults.
**Option B:** This option is incorrect because the oxygen saturation in the umbilical artery is not around 90-100%, which is the typical range for oxygen saturation in the pulmonary arteries.
**Option C:** This option is incorrect because the oxygen saturation in the umbilical artery is not around 0-10%, which is the typical range for oxygen saturation in the venous blood of the body.

**Clinical Pearl / High-Yield Fact**
A normal oxygen saturation in the umbilical artery is around 30-40%. This is an important indicator of placental function and fetal well-being. A low oxygen saturation in the umbilical artery can indicate fetal distress or placental insufficiency.

**Correct Answer: C. 30-40%**