Approximately 40% of all Americans may have spina bifida occulta, but because they experience little or no symptoms, very few of them ever know that they have it. The other two types of spina bifida, meningocele and myelomeningocele, are known collectively as "spina bifida manifesta," and occur in approximately one out of every thousand births. Of these infants born with "spina bifida manifesta," about 4% have the meningocele form, while about 96% have myelomeningocele form.