If you have diastasis recti either during pregnancy or after pregnancy, then you should not do the traditional Core exercises.
Generally, women don’t have this ab separation during the first trimester, but if you experience any discomfort in this area, you may want to modify the core exercises. You can find these modifications on Lindsay’s pregnancy DVDs. You should stay away from twisting motions, planks, quadruped positions, crunches and most traditional abdominal exercises. You will want to continue training the pelvic floor and transverse abdominis – these muscles act as a sling to support the baby and are extremely important in getting a flat stomach after the baby is born. You can activate the pelvic floor by controlling the flow of urine. And you can activate the transverse abdominis by placing a hand on our belly and forcefully saying the word “ha”. *Remember you should not do exercises lying on your back after the first trimester. (ACOG 2009)
Generally diastasis recti goes away after pregnancy once the pressure of the baby on the abdomen is gone. But if the diastasis (3-finger widths separation) is still present you should stay away from twisting motions, planks (not modified), crunches and most traditional abdominal exercises. You will need to train the pelvic floor and transverse abdominis to re-create the strength and integrity of your core. You can do this with pelvic floor training, supported crunches and TA training. These modifications are provided Lindsay’s PostNatal Packs and Pretty Fierce: Weight Loss 60 Day Program.