A critical period of fetal development happens during the early weeks of pregnancy, often before a person is aware they are even pregnant.
One of the earliest structures to form is the neural tube. This structure is flat at first. But it rolls into a tube by only 1 month after conception to become the brain and spinal cord.
Without enough folic acid, the cells in this structure can't function or grow correctly and the tube doesn't close. The spine, skull, and brain can be affected, with open or closed abnormalities.
Two of the most common types of neural tube defects (NTDs) are spina bifida and anencephaly. Spina bifida is a condition in which a part of the spinal cord and the surrounding structures develops outside the body, instead of inside it. Anencephaly is a condition in which the brain and skull bones don't form correctly. This results in most of the brain being absent.
Researchers have found that the risk for NTDs is significantly lowered when a person gets extra folic acid in addition to a healthy diet from 1 month before conception through 2 to 3 months after becoming pregnant.