If you’re pregnant — or even planning to have a baby — you need to know about folic acid. This type of vitamin B is crucial in preventing certain birth defects in the brain and spinal cord, called neural tube defects (NTDs). The neural tube starts out as a flat sheet of cells that normally folds into a tube and goes on to form the brain and spinal cord. The tube closes by the 29^th day after conception — before many women even realize they’re pregnant — but if it doesn’t close properly, NTDs are the result. That’s why it’s so important to start getting extra folic acid before you become pregnant.

Healthy women who can become pregnant should take a vitamin supplement containing 0.4 mg (400 micrograms) of folic acid every day. Most women only get about 0.2 mg of folic acid from foods, like grains, green vegetables (spinach, broccoli), meat (liver) and legumes (lentils and beans), so a supplement is the only way to be sure you’re getting enough. Women with diabetes, epilepsy, or a family history of NTDs, or who’ve already had an infant with a NTD should take 5 mg of folic acid daily under doctor’s supervision.

Once you’re positive that you’re pregnant, you should boost your daily folic acid intake to at least 0.6 mg, but don’t take more than 1 mg without checking with your doctor first. You’ll need more folic acid during pregnancy to help produce added blood cells and allow the fetus and placenta to grow rapidly. If you plan on breastfeeding, you should keep taking extra folic acid after delivery.