There is a common misconception that pregnant women cannot do an ab crunch or plank during pregnancy. This is not true! While there are some things to consider, and some modifications from your pre-pregnancy routine, it is safe and beneficial to keep your abs strong and to continue working your abdominal muscles during pregnancy.
During the first trimester, you can usually continue what you were doing prior to pregnancy, perhaps just lower the intensity and range of motion. If you were doing full sit ups, switch to crunches. If you were doing high-intensity ab exercises that involved quick twisting motions or throwing your body around, you probably want to find alternatives.
After your 20th week you no longer want to lie flat on your back. This is where the exercise ball comes in handy. By laying on the ball at an angle you can continue to work your abs throughout your pregnancy.
Remember that the movements are smooth, and the range of motion is small. Crunches are slow and controlled!
As always, talk to your doctor to make sure that it is safe for you to begin an exercise routine. Above all, listen to your body! Stop if something doesn’t feel right.