You'll probably start wearing maternity clothes in the middle of your second trimester — about week 15 to week 20. That said, every pregnancy is different, so go by how you feel. If you're carrying a bit lower, you'll most likely need a lower adjustment sooner. If you're carrying higher as I did with my first pregnancy, (not my second ha), you could potentially get away with the rubber band trick, belly bands and stretchy skirts for many months.