Thumb duplication is a form of polydactyly (an extra digit in the hand or foot) in syndrome, especially if your child's thumb has three bones instead of two. An extra thumb can often be seen by ultrasound prenatally, and by eye at birth.
Thumb duplication is a congenital condition (meaning that your baby was born with it) in which.
Babies with thumb duplication (or thumb polydactyly) are born with an extra thumb on one or both hands. A thumb duplication is more of a split thumb rather than an "extra thumb." Thumb duplication happens before a baby is born.
Children born with thumb duplication (also called preaxial polydactyly or radial An extra thumb is often present on both hands, but some children may just have most common congenital hand anomalies, occurring in 1 in every 3, births.