According to the CDC, most developmental delays come from a mixture of factors. The most common factors are: - Genetic issues - Infections during pregnancy, like cytomegalovirus  - Birth complications - Smoking or drinking during pregnancy  - Exposure to toxins during pregnancy, like lead Most of the time, doctors aren’t able to tell exactly what caused a child to have developmental delays. However, we do know that the top causes of intellectual disabilities are fetal alcohol syndrome, genetic conditions, and infections.  Also, 25% of hearing loss in babies comes from maternal infections, head trauma, and complications after birth.