The major types of birth defects are structural and functional, according to MedicineNet. Structural defects cause physical abnormalities, such as a cleft palate, while functional defects interfere with how an organ or body system works, such as Down syndrome. Other subtypes include metabolic, sensory, nervous system, degenerative and neural tube defects.
As of 2015, doctors have classified more than 4,000 birth defects, states KidsHealth. Heart defects are common structural problems that occur when essential parts of the cardiovascular system aren’t fully developed. For example, atrial or ventricular septal defects are holes in the walls of the heart chambers. Another common structural defect is a cleft palate, an abnormal opening between the upper lip and nose that forms when mouth tissues don’t develop properly. Spina bifida is a neural tube defect that develops when the spinal column doesn’t provide complete coverage of the spinal cord.
Some defects have genetic or environmental causes, such as infections, and many are preventable with proactive prenatal care, notes KidsHealth. A child may inherit defects from a mother with a genital herpes infection, such as brain damage, vision impairment and the muscular deformity cerebral palsy. Down syndrome is a genetic functional defect caused by an extra chromosome, leading to mental retardation, irregular physical characteristics and health problems.