Health Canada recommends that pregnant women, or women who are trying to become pregnant, take a multivitamin containing 400 mcg (0.4 mg) of folic acid (vitamin B9), vitamin B12 and 16 to 20 mg of iron.
This recommendation is designed to prevent the most common nutritional deficiencies and, ultimately, to avoid the development of certain congenital defects.
Taking 400 mcg of folic acid before and during pregnancy reduces the risk of spina bifida, a birth defect characterized by the abnormal formation of the neural tube (the structure permitting development of the brain and spinal cord). This birth defect often leads to severe handicaps or intellectual disabilities.
Folic acid has the ability to mask a deficiency in vitamin B12. As a precaution, it is recommended that the prenatal multivitamin also contain B12. This is especially important for pregnant women who consume little or no animal products, such as meat, fish, milk or eggs. Vitamin B12 deficiency can cause anemia, cognitive difficulties and other permanent neurological problems.
The increased need for iron in pregnant women cannot be met by food alone. Taking a multivitamin, combined with a diet composed of iron-rich foods (meat, poultry, fish, legumes), helps meet the daily requirement for iron, which is 27 mg/day. A sufficient intake of iron diminishes the risk of premature delivery, low birth weight and newborn mortality.
In addition, a prenatal multivitamin containing 400 IU of vitamin D allows pregnant women to fulfill their vitamin D needs. Vitamin D increases the absorption of calcium. An adequate intake of vitamin D diminishes the risk of hypocalcemia in mothers and the risk of rickets and dental abnormalities in newborns.
Multivitamins should contain less than 10,000 IU of vitamin A in order to avoid the toxicity associated with too large a dose of this vitamin, which can cause congenital abnormalities.
Finally, scientific literature has shown that taking a prenatal multivitamin–instead of a supplement of iron and folic acid separately–reduces the risk of low birth weight.