Why wait for 40 weeks? Why wait for labor to start on its own, if you and baby are health? Here is some great information for your consideration!
Babies born by induction before 40 weeks have a much higher chance of breathing and eating problems after birth. They have a much higher chance of learning disabilities and behavior problems down the road.
http://www.acog.org/About_ACOG/News_Room/News_Releases/2011/Fight_Prematurity_with_Awareness_-_Longer_Pregnancies_Ob-Gyns_Say (ACOG states inductions without medical reason should never happen before 39 weeks)
http://www.health4mom.org/a/40_reasons_121611 (Great info on the benefits of waiting for spontenous labor!)