Amniocentesis detects or rules out Down's syndrome, which causes mental retardation, congenital heart defects, and physical characteristics such as skin folds near the eyes. Amniocentesis also detects neural tube defects such as spina bifida. Babies born with spina bifida have a backbone that did not close properly. Serious complications of spina bifida can include leg paralysis, bladder and kidney defects, brain swelling (hydrocephalus), and mental retardation.

If your pregnancy is complicated by a condition such as Rh-incombatibility, your doctor can use amniocentesis to find out if your baby's lungs are developed enough to endure an early delivery.