As PP said, definitely talk to your OB about it. I wish I had some links to share but I just don't. I will tell you that I learned about diastasis recti (just in case someone doesn't know what that is--it's separation of the abdominal muscles) the hard way. Some of you may know this but for those who don't I have 5 kids. . .#4 & #5 are twins. So as your belly expands your abdominal muscles separate. It doesn't happen to every one but the more pg you have and the less in shape you are (

or if you pop out two at a time!) the more likely you are to get it.
To give a clearer picture (if this helps) diastasis recti is what is happening when a woman still looks pg. So like in my case. . .my twins are two and I still look a little pg sometimes.
In any case to correct or prevent the issue pilates is very good bc it focuses on 'sucking' in your tummy. The action actually helps bring the muslces together. Crunches separate the muscles which again if you're not pg or you're not recovering. . .is pretty normal.
Am I clear? I am so sleepy I can't tell which way is up. I hope that answered the question!