WHO has issued new guidelines for folate concentrations for women of reproductive age. Each year, about 300,000 babies worldwide are born with neural tube defects (NTDs), but adequate daily consumption of folic acid before and during early pregnancy has been shown to significantly reduce the risk for NTDs. The new guidelines state that at the population level, red blood cell (RBC) folate concentrations should be greater than 400 ng/mL (906 nmol/L) in women of reproductive age to achieve the greatest reduction of NTDs. In addition, that RBC folate threshold can be used as an indicator of folate insufficiency in women of reproductive age. WHO added that no serum folate threshold is recommended for prevention of NTDs in women of reproductive age at the population level. In addition, microbiological assay is recommended as the most reliable choice to obtain comparable results for RBC folate concentration across countries. In the United States, folic acid is obtained from three sources: fortified foods, ready-to-eat cereals, and supplements.