T-shaped internal incision

I have a t-shaped internal incision from my first c-section.  So I am not a vbac candidate and had my csection scheduled for 39 weeks.  (My obgyn said that was the earliest try could schedule). Today I had a meeting with a perinatologist because I have GD and he was adamant that my csection needs to be changed to 37-38 weeks because of the t-shaped incision and the high risk of uterine rupture (my GD is diet controlled and baby is measuring normal at almost 34 weeks).  He said this is standard practice.  I don't meet with my obgyn until Tuesday.  Has anyone had experience with a t-shaped internal incision and a repeat csection--is between 37-38 weeks what you were told?  I'm a little upset with my obgyn for "missing" this!  This is the same obgyn I used for my first pregnancy.