<1 % According to cdc, autism rate is 1 in 150-500 children, more males than females. Mental retardation is 9.7 in 1000 children. Cerebral palsy is 2.8 in 1000 children. So chances are low, if your child is meeting all the development milestones. The chances are higher with prematurity, family history of development disorder, and if the child does not meet the development milestones.
Usually low. About 3-5% of pregnancies are associated with a congenital anomaly; many of these have delays. 5-10 % of pregnancies that survive to term may show evidence of prenatal or perinatal (during labor and/or delivery) that can lead to developmental delays. Prematurity and problems in the nursery can also increase the risk for developmental delasy.