There are thousands of birth defects, each with its own unique signs and symptoms. Defects can affect nearly any part of the body, and generally have an effect on the body’s structure, function or metabolism. They may occur alone or in groups. Some birth defects are obvious immediately after birth, while others may not be discovered until later childhood or even adulthood. Some may not demonstrate any signs or symptoms, or may not show signs or symptoms until childhood or adulthood. Because of the wide range of birth defects, nearly any problem (e.g., poor feeding, nonresponsiveness, irritability) could potentially be a sign or symptom of a birth defect. Some other common signs and symptoms of birth defects include:

• Abnormal physical structure. Structural defects result in abnormal physical properties. These may be external, such as misshapen ears or too many fingers or toes. They may be internal, such as with missing or malformed organs. Many structural defects may be obvious both internally and externally, such as with defects in the skull that cause an abnormal shape of the head or face. Musculoskeletal problems or paralysis may be less apparent before a child learns to crawl.
  
  
• Mental impairment. Many birth defects result in learning disabilities or mental retardation. These defects may not become apparent until an infant gets older and appears to be missing developmental milestones associated with a given age. Learning disabilities may not be noticed until a child is 4 or 5 years old.
  
  
• Sensory impairment. Blindness and/or deafness may occur due to a birth defect. This may be due to structural defects in the eyes and/or ears or problems with the central nervous system.
  
  
• Irregular heart rhythms. Murmurs and irregular heart rhythms may be caused by heart defects.
  
  
• Hormone or enzyme deficiencies. Many birth defects result in hormone or enzyme deficiencies. Many of these may be detected in blood, urine or fecal tests. Some enzyme disorders may not be detected until much later, when the child suffers some sort of attack or experiences mental retardation because of malfunctioning enzymes.