Is it better to schedule a third c-section at 37, or 38 versus the full 39 or 40 weeks?

Yes and no: The American Congress of Ob/Gyns recommends that elective c/sections not be performed prior to 39 0/7 weeks. If there is a medical reason such as diabetes or hypertension, the c/section may be performed earlier. There is some very recent data hinting that a repeat c/section earlier than 39 weeks may avoid some problems but this very preliminary information and additional studies will be needed.