Stretching is fine also there is some yoga you can try...if you use any weights keep it minimal and think more cardiovascular....try light treadmill ....sitting toe touch....also great one is sit in an invisible chair against the wall....so squat place back on wall and keep knees 90 degrees ...like your sitting in q make believe chair great for legs and butt and tummy without having to strain with weights
I still Jazzercise 4 times a week and I'm 13 weeks along. You can keep doing your pre-pregnancy workout if your body is used to it. If you're starting from scratch, try walking or water aerobics. Water aerobics is actually awesome during pregnancy! I was told no flat-on-your-back abs after the first trimester, and not to get my heart rate over 160bpm.
It depends on your pre-pregnancy fitness level. The most important thing is to not overheat and later, activities that rely on good balance (e.g., snow/ice sports) or heavy lifting. Swimming, walking and yoga are all highly recommended for most pregnant women.
Work out is good. But need to watch it also coz first trimester is the most critical of pregnancy...make sure ur not doing too much.