When to induce labour?

Honestly I Myself personally Have not heard of anyone Being Induced For A Non medical reason Until They at least reached 39 Weeks. I Had Gestational Diabetes with my children and even with It The first Baby They let me go tell 40 weeks before induction and then with My Second They we're going to induce at 39 weeks the soonest they we're able to But my little one decided to come on her own at 37 weeks. With my 3rd again they we're going to induce the soonest they could and He came at 38 weeks 3 days on his own. Like I said though I have actually Not Heard of any places Inducing before 39 weeks unless it was a serious reason They had to induce or c-section for even with Gestational diabetes they still Would not and did not want to induce tell 39 weeks.