The diagnosis of an intellectual disability is typically made through a test of intelligence or cognition, often assed by the range of scores on an Intelligence Quotient (IQ) test.1 This type of test will help the health care provider examine the ability of a person to learn, think, solve problems, and make sense of the world.2 Average IQ test score is around 100, while 85% of children with an intellectual disability score in the range of 55 to 70.3 More severe cases of intellectual disability generally have lower IQ scores.
Clinicians will also observe a child’s behavior for signs of a disability and assess adaptive behavior. Adaptive behaviors include coping skills and other behaviors that show how a child interacts with other people.2 Health care providers can use this information to assess whether the individual has the skills needed to live and interact well with others.
Some conditions that lead to IDDs may be diagnosed with a blood test, ultrasound, or another method, depending upon the condition. These tests may be conducted after birth or during pregnancy.
Newborn screening relies on testing blood samples taken from newborns while they are still in the hospital to help identify certain serious or life-threatening conditions, including some that lead to IDDs. Most tests use a few drops of blood obtained by pricking the infant’s heel. If a screening test suggests a problem, the infant’s doctor will follow up with further testing.4
To learn more about newborn screening, visit the Newborn Screening Translational Research Network website at https://www.nbstrn.org/ or the Centers for Disease Control and Prevention webpage at http://www.cdc.gov/ncbddd/birthdefects/diagnosis.html.
Health care providers recommend that certain pregnant women, including those who are older than 35 years of age and those with a family history of certain conditions, have their fetuses tested for conditions that cause IDD prenatally, while the fetus is still in the womb. There are two main types of prenatal tests.
Amniocentesis (pronounced am-nee-oh-sen-TEE-sis) is a test that is usually performed to determine whether a fetus has a genetic disorder. In this test, a doctor takes a small amount of fluid from the womb using a long needle. The fluid, called amniotic (pronounced am-nee-OT-ik) fluid, contains cells that have genetic material that is the same as the fetus’s genetic material. A laboratory grows the cells and then examines their genetic material for any problems. Some IDDs that can be detected with amniocentesis are Down syndrome and certain types of muscular dystrophy.
Because amniocentesis can cause a miscarriage in about 1 out of 200 cases, it is usually only recommended for pregnancies in which the risk of genetic disorders or other problems is high.
This test extracts cells from inside the womb to determine whether the fetus has a genetic disorder. Using a long needle, the doctor takes cells from the chorionic villi (pronounced KOHR-ee-on-ik VILL-i), which are tissues in the placenta, the organ in the womb that nourishes the fetus. The genetic material in the chorionic villus cells is identical to that of the fetal cells.
Like amniocentesis, CVS can be used to test for chromosomal disorders such as Down syndrome and other genetic problems. CVS can be done earlier in pregnancy than amniocentesis, but it is also associated with a higher risk of miscarriage—about 1 in 100 cases. Health care providers usually only recommend CVS in women who are at high risk for a condition or IDD.