Neural tube defects are prevented by –
**Core Concept**
Neural tube defects (NTDs) are congenital anomalies resulting from the failure of the neural tube to close during embryonic development. This process occurs within the first month of gestation, and the primary risk factor for NTDs is a deficiency in folic acid.
**Why the Correct Answer is Right**
Folic acid supplementation has been widely recommended for pregnant women to prevent NTDs. This is because folic acid is essential for the synthesis of tetrahydrofolate, which is necessary for the methylation of homocysteine to form methionine. Methionine is then converted to S-adenosylmethionine (SAMe), which is required for the methylation of DNA and proteins, including those involved in neural tube closure. The recommended daily dose of folic acid for pregnant women is 400-800 μg, starting at least 1 month before conception.
**Why Each Wrong Option is Incorrect**
**Option A:**
This option is incorrect because while vitamin B12 is also involved in the methylation of homocysteine, it is not the primary nutrient responsible for preventing NTDs.
**Option B:**
This option is incorrect because although iron is essential for numerous bodily functions, it does not play a direct role in preventing NTDs.
**Option C:**
This option is incorrect because while vitamin D is crucial for bone health and development, it is not directly involved in preventing NTDs.
**Clinical Pearl / High-Yield Fact**
It is essential for pregnant women to start folic acid supplementation at least 1 month before conception, as this allows sufficient time for the folate stores to be replenished and for the neural tube to close properly.
**Correct Answer: D. Folic acid.**