39 Weeks Pregnant – signs of labor. This week may well be your last week of pregnancy, and your baby is ready to join you in the world! Find out what’s happening to you and your baby at 39 weeks’ pregnant. How big is my baby at 39 weeks? Your baby is the size of a small pumpkin, and is now officially full-term. Your baby will now weigh between seven and eight pounds, and measure between 19 and 21 inches from top to toe. She won’t grow much more now, but her brain is still growing at a rapid pace