I've been currently babysitting my 2 1/2 year old sister which weighs about 50-60 Lbs, she is very hyper and is very hard to deal with, I put a lot of pressure on my belly and have to lift her many times to change her because she doesn't like to get her diaper changed and we are currently potty training her, but I'm scared because I've heard that a lot of lifting heavy objects while pregnant can result into preterm birth.