This source provides a comprehensive review of the evidence regarding folic acid supplementation for preventing neurodevelopmental defects, emphasizing its established role in preventing neural tube defects (NTDs), which has led to a global consensus for daily intake of 400–800 µg for all women of childbearing age. Beyond NTDs, the text examines the expanding research linking adequate maternal folic acid to improved cognitive outcomes and a reduced risk of disorders like Autism Spectrum Disorder (ASD) and Attention-Deficit/Hyperactivity Disorder (ADHD). However, it introduces the complexity of a potential U-shaped risk curve, noting that both deficiency and excessive intake may be detrimental and that the efficacy and safety of folic acid are critically dependent on its metabolic partner, Vitamin B12, highlighting the need for a balanced "metabolic optimization" approach. Finally, the source discusses the ongoing debate between synthetic folic acid and the active form, L-methylfolate, particularly for individuals with MTHFR gene variations.