Every woman is different. If you're a first-time mum, you could begin developing a baby bump any time between 12 and 16 weeks. But if this isn't your first baby, you may start showing sooner. At 16 weeks of pregnancy, your uterus will be stretching to fit your growing baby. Jul 15, - And I gained 50 lbs my pregnancy, so it will hit you all of a sudden probably. Its like one day i went to sleep not really showing and I woke up.