## Core Concept
The question revolves around the genetic counseling aspect of spina bifida, specifically focusing on the recurrence risk for a couple with a previously affected child. Spina bifida is a type of neural tube defect (NTD) that results from the incomplete closure of the neural tube during embryonic development.

## Why the Correct Answer is Right
The recurrence risk of spina bifida for a couple with one previously affected child is approximately 3-5%. This increased risk is due to the multifactorial inheritance pattern of neural tube defects, which involves both genetic and environmental factors. The exact mechanisms are not fully understood, but it is believed that genetic predisposition plays a significant role, along with potential environmental triggers.

## Why Each Wrong Option is Incorrect
- **Option A:** A 0% recurrence risk would imply that there is no genetic or familial component to spina bifida, which contradicts the established understanding that there is a multifactorial risk involved.
- **Option B:** A 10% recurrence risk seems higher than the generally accepted risk, which is in the range of 3-5%.
- **Option D:** A 50% recurrence risk would suggest an autosomal dominant pattern of inheritance, which does not apply to spina bifida.

## Clinical Pearl / High-Yield Fact
A key point to remember is that the recurrence risk for neural tube defects like spina bifida can be significantly reduced (by up to 70%) if the mother takes folic acid supplements before conception and during early pregnancy. This is a critical piece of advice for couples seeking preconceptional counseling, especially those with a history of NTDs.

## Correct Answer: C. 3-5%