Birth defects like Spina Bifida occur in 7 out of every 10,000 live births in the United States.  Birth certificate data from the National Vital Statistics System, a component of the Centers for Disease Control and Prevention (CDC), National Center for Health Statistics (NCHS), indicate a drop in the rate of Spina Bifida; however, Spina Bifida is considered to be underreported on birth certificates so the drop in the rate could be due to lack of reporting, not an actual decrease in occurrence.  In addition, a number of Spina Bifida pregnancies are voluntarily terminated and we cannot be certain how many pregnancies are terminated versus carried to term. 

For more information on this question and other related topics, SBA offers a series of fact sheets and publications. Additional questions or requests for information should be sent to the SBA National Resource Center.