Low plasma B6 and B12 are associated with increased risk of early spontaneous abortion. Studies have shown that women with low folate levels are at increased risk of miscarriage, whereas women with higher folate levels showed no increased risk of miscarriage. Folate and B12 deficiencies have been known to cause birth defects. Inadequate maternal vitamin B12 status is associated with a significantly increased risk for neural tube defects. It is suggested that women have vitamin B12 levels of >300 ng/L before becoming pregnant.