It is well known that a diet containing at least 400 mcg of folate is important pre-conception and during the first month of pregnancy, particularly as it pertains to reducing the incidence of Neural Tube Defects (NTDs) like spina bifida. Since the FDA mandated fortification in the US of all cereals and grains with 140 mcg of folic acid per 100g of grain in 1996, the incidence of NTDs decreased 19-50%. NTDs are a result of inadequate closure of the neural tube in early fetal development, and is usually complete the 28th day of pregnancy. Does this mean that this level of folate intake is needed beyond the first month or even the first trimester?

The answer can be deduced from a study measuring folic acid and 5-methyl-tetrahydrofolate (5-MTHF) after non-pregnant, lactating and women in their third trimester of pregnancy were given a prenatal vitamin containing 750 mcg folic acid for 10 - 12 weeks, which combined with a diet containing 400 mcg adds up to a total intake of 1,150 mcg (folic acid and folate). Because folic acid is 1.7 times more bioavailable than folate, this amounts to 1,675 Dietary Folate Equivalents (DFEs). 24 hour urinary measurements for total folate excretion were analyzed in all three groups (pregnant, non-pregnant and lactating women) at baseline, in the middle and at the end of the study.

The results were very interesting in that pregnant and lactating women excreted significantly less total folate than the non-pregnant women (p<0.004) and the pregnant women excreted less than the lactating women. The pregnant women excreted 9% of the daily folate intake (1150 mcg) whereas lactating women excreted 20% and non-pregnant women excreted 43% of their daily dose - or about 60% of the administered dose of prenatal vitamin. This implies that even in later stages of pregnancy, the maternal and fetal requirements for folate is substantially higher, resulting in more folate being extracted from the mother, leaving much less to be excreted. Additionally, nursing mothers also are using more folate to enrich their breastmilk resulting in lower excretion rates as compared to non-pregnant women.