B

Randomized trials and multiple systematic reviews show that taking folic acid (folate) in the pre-conception period (≈0.4–4 mg/day) lowers the risk of both first occurrence and recurrence of neural tube defects, whereas vitamins A, C, and E have no such proven benefit [Rieder, 1994, PMID 7982331; Valentin et al., 2018, PMID 29433770].