Exceeding the normal length of pregnancy has no damaging influence on the fetus as long as the placenta remains able to function. It results, though, in especially large and heavy newborns. One distinguishes between a relative and an absolute post-term delivery.
In a relative post-term delivery the relationship between the nutritional demands of the fetus and the corresponding output of the placenta is disturbed.
In an absolute one the duration of the pregnancy is longer than 40 weeks (or 42 weeks after the LMP).
Most often, the placenta output is insufficient due to degenerative changes. The consequences are a nutritive dysfunction and thus deficiency for the child. In a relative post-term delivery this occurs already before the normal end of the pregnancy.