In some cases, prenatal tests (e.g., blood tests, ultrasound) may indicate whether a child may have a condition (e.g., a birth defect) that can cause mental retardation. For instance, ultrasound is among the most common prenatal tests. A fetal ultrasound can indicate whether a fetus may have Down syndrome.

Amniocentesis may also be performed to evaluate the likelihood of mental retardation. In amniocentesis, a needle is inserted into the uterus through the mother’s abdomen and a sample of amniotic fluid is extracted for testing. Chorionic villus sampling (CVS), which involves removing a sample of the placenta, may also be useful. Karyotypes (tests that allow a physician to evaluate the patient’s genetic structure) can be performed using both amniocentesis and CVS.

Diagnosing mental retardation after birth relies on an evaluation of how well the patient thinks and functions. A certified psychologist is typically required for an accurate diagnosis. This psychologist must be able to give, score and interpret standardized intelligence tests for the individual child and must be able to observe the child for how well he or she functions in daily life.

Several different standardized intelligence tests are available, with different tests appropriate for different ages. The Wechsler Intelligence Scales are the most commonly used intelligence tests for children older than 3 years. The Wechsler Scales include separate tests for children older and younger than 6 years, although a functional age is more important than a chronological age in this division.

This means that a child of 7 years who functions on a level closer to children of 5 years would be given the test directed towards the younger children. The Stanford-Binet Intelligence Scale may be used instead of the Wechsler Scales for school-aged children. Both of these scales focus on verbal skills. The Wechsler Scales also evaluates general performance skills, while the Stanford-Binet Scale evaluates thinking, memory and reasoning skills. The scores of different intelligence tests do not typically correlate with each other. In general, the tests for school-aged or older children are much more accurate than those for younger children.

While observing the child, the psychologist will be looking for self-care skills (e.g., toilet training, eating, dressing), communication skills and social skills. These skills may also be evaluated using a test called the Vineland Adaptive Behavior Scale. If the child is under the age of about 3-1/2 years, the Bayley Scales of Infant Development may be used.

Children who may have mental retardation also require a thorough examination, including a physical examination and an evaluation of their medical history. The medical history evaluation typically includes a thorough developmental history, including the progress of the pregnancy and delivery of the child. The child will also require periodic re-evaluations to monitor the condition. This allows any changes that may affect treatment to be noted.

Children with mental retardation are frequently tested for underlying conditions (e.g., Down syndrome, Fragile X syndrome) that may have caused their retardation. However, this is not always necessary or beneficial. Many causes of mental retardation are unknown, so many of these tests cause further financial and other burdens to the child’s family without providing any information. Physicians take many factors into consideration when deciding whether or not to perform these additional tests. These factors include the severity of the child’s mental retardation, whether or not the child appears to be at risk for a condition or a diagnosis seems likely, and parental concerns.

Testing is also more important if the child’s parents intend to have more children. If the mental retardation has a genetic cause, subsequent children may be at an increased risk of mental retardation as well.

Various tests may also be employed in an attempt to determine the cause of the mental retardation. This may include neuroimaging, blood tests and electroencephalograms (EEG). Karyotyping may be needed for children who may have a genetic disorder related to their chromosomes. If a condition that increases a child’s risk for mental retardation was noted during newborn screening tests, tests may be performed to ensure that it is still under control.