I want a baby so badly!

how can i convince my husband were ready to have a baby? we r together for 4 tears, he has always known i wanted kids and agreed he did too, but now were married he's changed his mind! he says its because he doesn't want me to put weight on as ive worked so hard and lost almost 10 stone in 2 years. but inside im longing to be a mother and feel he would be a great father he's just scared how can i convince him he will be a good dad?