Horizontal exercises like dead bugs and sit-ups require you to lie on your back, says Colleen Conlon, a group fitness instructor at Equinox locations in New York City who is certified in pre- and post-natal training. In that position, all the weight from the growing uterus puts pressure on your back and minimizes blood flow to your lower body.
Other core moves (think: side planks and single-leg bodyweight deadlifts) rely on balance, a skill that becomes increasingly difficult as your center of gravity changes, she adds.
The bottom line:
Once you’re halfway through your second trimester, maintain core strength with standing exercises such as cable chops, windmills, halos, and kettlebell swings (if they were part of your pre-pregnancy routine), Conlon says. Choose one or two exercises and perform 3 to 5 sets of 12 reps as often as every day.