When will my baby start to unclench his fists?

Grasp reflex. Babies start losing their grasp reflex around 2 to 4 moths and gone at 6 months.
3 months. This clenching of the fists is called the "hand grasp." it is a primitive reflex that disappears at roughly 3 months of age. In almost all infants it gone by 4 months of age. If not, it can be an early sign of cerebral palsy. If your baby still has this at 4-5 months of age, please bring it to the attention of your healthcare provider.