Questions for doctors: does conception before decreasing hgb A1c cause miscarriage or birth defects?

Hgb A1C. Poorly controlled diabetes correlating to an elevated HGB A1c has been associated with a higher risk of congenital heart defects as well as other birth defects. There is no correlation with genetic abnormalities. Good diabetic control for at least 6 months prior to trying to conceive will achieve the best outcome.
Possibly. Risk of miscarriage and birth defects increase with increasing HGB a1c. Thus, if HGB A1c is elevated, it is recommended to control the diabetes prior to conceiving.