I agree with PZ. I was induced with DD1 when I was 40+4 and it was an extremely long, drawn out process because she simply wasn't ready, and that was even when she was technically overdue.

I too would be wanting a very good reason as to why he wanted to induce you around the 38 week mark - something far more involved than simply "because you have GD". A gf of mine had her bub in January and she was 39 weeks with GD. DS was born just over 3kgs so a diagnosis of GD doesn't necessarily mean a big baby. So long as your amniotic fluid levels are good, you're ok and bubs isn't stressed I don't see the point. Women who don't have GD relatively regularly give birth to 4.5kg + bubbas.