Once a baby has inherited the gene abnormality responsible for fragile X syndrome (FXS), there is no way to prevent the condition or its symptoms.

Prior to conceiving a child, parents can have genetic testing performed to identify whether either parent is an FXS carrier and determine the likelihood of conceiving a child with the condition. A physician may take a detailed family history before performing DNA tests that can help identify whether a man or woman is a FXS carrier. Depending on the outcome, a couple may opt not to have children to avoid having a child with FXS.

If a person is identified as an FXS carrier, other members of their family should also be tested, since their children may be at risk. For example, a male carrier will transmit the gene mutation to all his daughters (who themselves become carriers). These women are then at risk of having children born with the full-blown syndrome. Thus, a woman identified as a carrier may have sisters who are also carriers and who may also have children with FXS.