it doesn't happen on compulsory basis. when the pregnancy progress the abdomen stretches and the layers of skin gives way and collagen formation is poor there. you can use simple coconut or olive oil to make the stretch marks look better by mildly moisturizing the area but physical stretch cant be by passed and its something natural but the real treatment is the after you stop your breast feeding - advanced treatment option available in cosmetic gynecology.

Ya it is. Compulsory. Apply olive oil.