Unlike the comic books, rapid mutation mostly produces the kind of results you definitely do not want
Not all birth defects are mutations; however, all mutations are birth defects.
Mutations can be minor or major, and they can be beneficial or negative -- up to and including fatal. Usually cells have the ability to correct and repair mutations in the DNA sequence if caused during the "copy and split" process as cells divide.
The type of birth defect determines its sub-classification. If the defect is caused by a change in the DNA sequence, then it's considered a mutation.
Mutations occur naturally. Other birth defects occur as a result of external causes:
Fetal alcohol exposure
Toxic substances
Medications and supplements
Environmental toxical substances
Paternal smoking
Infections
Lack of nutrients
Physical restraint
Genetic causes (often inherited)
Socioeconomic status
Radiation
Father's age
Unknown or multifactorial