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MTHFR mutations have been linked in some studies to an increased chance of having a baby with a neural tube defect (spina bifida). One study suggested that mothers with 2 MTHFR mutations were twice as likely to have a baby with a neural tube defect, whereas other studies have not supported this finding. Recent research has implied that risks vary, based on the nutritional status of the mother (ie, folate levels, vitamin intake) and whether or not she has an elevated homocysteine level. Because of this controversy, some practitioners may recommend extra folate supplementation (usually 4 mg) for women with 2 MTHFR mutations, whereas other practitioners will recommend normal use of prenatal vitamins containing folic acid for a woman who does not have an elevated homocysteine level.
There is also conflicting evidence about the relation between homozygous MTHFR mutations and pregnancy complications (including preeclampsia, placental abruption, recurrent pregnancy loss, and intrauterine growth restriction, as described earlier). A recent meta-analysis, which combined all of the data from these studies, found that there was not an association between MTHFR and recurrent pregnancy loss. It seems that homozygous MTHFR may moderately increase the risk of preeclampsia and placental abruption, but more research in this area is necessary. Although it is not standard medical practice to test for MTHFR mutations when a woman has a history of these complications, some practitioners may order this testing.
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Originally Posted by WomensHealth.Gov (Folic Acid Fact Sheet)
Can women get too much folic acid?
You can't get too much folic acid from foods that naturally contain it. But unless your doctor tells you otherwise, do not consume more than 1,000 mcg of folic acid a day. Consuming too much folic acid can hide signs that a person is lacking vitamin B12, which can cause nerve damage. Lacking vitamin B12 is rare among women of childbearing age. Plus, most prenatal vitamins also contain B12 to help women get all that they need. People at risk of not having enough vitamin B12 are mainly people 50 years and older and people who eat no animal products.