There are over 4,000 different kinds of birth defects, and about 1 in every 33 babies born in the US each year will have some sort of defect. Birth defects that involve missing or deformed body parts are called structural defects. Those that involve problems with a baby's chemistry are called metabolic defects. They can be caused by the passing down of certain genes for that specific disease from the parents. If a parent has the disease, their babies will usually also develop that same disease. However, environmental factors can also cause birth defects in babies. For example, if the mother smokes or drinks alcohol during pregnancy, the baby will most likely develop a genetic disorder. It is important for mothers to consider their risk factors for their child developing a medical condition, and they should always do what they can to prevent that. Doctors suggest that they take folic acid while pregnant, and mothers should avoid drinking, doing drugs, smoking, and harmful medications to the baby.