Youtube prenatal pilates, I'm just about 21weeks and i do the 10minute pilates but i do the one that's a full hour, has all of them in one video. It works your whole body and abs without doing harmful abb excersises. Its good to strengthen your abs and body and it also shows you stretches and breathing that help with my back pain! I love it
You can do ab work in modified form, planks are good, check out you tube for prenatal exercises I have found some great ones.
Where would I find prenatal yoga?
No crunches or anything like that try prenatal yoga and squats work out those muscles without the high impact