Sweets, rice, fermented prouducts like idly etc, Chinese, potatoes ye Sab bhi band karna hoga. Strict diet follow karna Jaruri hai. Or else delivery ke time pe bahot dikkat Ho Sakti hai if c-sec karne ki jururat pade to Aur bhi jyada.. And diabetic mothers k baby k chances h ke vo bahot jyada unwanted weight put up Kar Sakta hai, ya obese Ho..... And if metformin is not working doctors might suggest u for Insulin 2 times a day in your belly or thigh......
Best to consult your gynaecologist as he will be able to give you proper advice