The gestation period is anywhere for 38-40 weeks. It could be that your conception date is off a little, or the baby is ready to come out. Having a baby a week early (39 weeks of pregnancy) will not harm the baby.
If a doctor wants to induce labor that means the baby needs to come out, and it might be harmful for the baby to stay in.
Premature birth is considered to occur when the baby is born sooner than 37 weeks after the beginning of the last menstrual period.
42 weeks of pregnancy is considered postmature birth.