Final answer:
The 5th percentile refers to a statistical measure used to interpret growth and development in children. In this case, it means that the child's heart defect is less severe compared to the majority of other children with congenital heart defects.
Step-by-step explanation:
The 5th percentile refers to a statistical measure used to interpret growth and development in children. In this case, the mother is likely asking why her 3-year-old child's condition falls at the 5th percentile. The 5th percentile means that the child's condition is lower than 95% of other children in the same age group. It suggests that the child's heart defect may be less severe compared to the majority of other children with congenital heart defects.