## Core Concept
Folic acid supplementation is crucial in preventing neural tube defects (NTDs) such as spina bifida and anencephaly. Neural tube defects occur very early in pregnancy, typically within the first month, before many women even know they are pregnant. The critical period for neural tube formation is between 21 and 28 days post-conception.

## Why the Correct Answer is Right
The correct answer emphasizes that folic acid supplementation should start at least one month before conception to be effective in preventing neural tube defects. This timing is critical because the neural tube closes about 28 days after conception, and adequate folic acid levels are necessary during this period to prevent defects. Folic acid is essential for DNA synthesis and repair, and its deficiency can lead to improper neural tube closure.

## Why Each Wrong Option is Incorrect
**Option A:** This option suggests starting folic acid supplementation after confirmation of pregnancy, which is too late for preventing neural tube defects since the critical period for neural tube formation would have already passed.

**Option B:** This option implies starting folic acid at the time of conception or shortly after, which might still be too late for some women, especially those with unplanned pregnancies or irregular menstrual cycles.

**Option D:** This option suggests a later start than option C, making it even less effective in preventing neural tube defects.

## Clinical Pearl / High-Yield Fact
A key point to remember is that all women of childbearing age who are capable of becoming pregnant should take a daily supplement containing 400 to 800 micrograms of folic acid, in addition to consuming a healthy diet, to reduce the risk of neural tube defects. This recommendation is particularly important for women who are planning to become pregnant.

**Correct Answer: C. One month before conception.**