A neural tube defect is when the baby's spine or skull isn't formed properly, or when the spinal cord or part of the brain develops outside the body. Spina bifida is one type of neural tube defect. Every pregnancy is screened for neural tube defects, usually around the 20th week, either with a blood test or an ultrasound, so the defects are likely to be identified then. Taking folic acid in the weeks before and after conception is the only thing that's been shown to reduce the risk of neural tube defects. It is commonly recommended to take a supplement of about 400 micrograms of folic acid daily.