hi E.! i'm happy to respond to your post and tell you about my experience: i had two vaginal births, over 20 yrs ago ago, and never worried about getting my abs in great shape after that; i've always struggled with my weight so there've been times when i've been 100 pounds overweight, and times when i've been in good shape (it's a lifelong rollercoaster), then i had another baby by c-section nearly 4 yrs ago and got very big again, had the abdominal muscle separation you're talking about (where if you're laying down and contract your abs, they pop up in the middle), and did in fact develop an abdominal hernia, sustained for over a year, which ultimately had to be repaired; having the c-section - since it is an abdominal surgury - is considered a risk factor for developing an abdominal hernia, however you don't sound overweight, so that helps you out a lot (not having fatty tissue pushing behind the weak muscle and hanging off the muscle is a big plus for you)...when my hernia had just started, a doctor thought it was just the seperation of muscles you're talking about, and advised me to strengthen my abs w/exercise: ultimately i increased the size of my hernia doing that, and as it really is nearly impossible to get those muscles back together like they were pre-babies/surguries i wish i had been more careful and i wish the doctor had caught my hernia earlier...so i guess my advice would be to be careful! as the other mama mentioned, doctors don't give us the "extra care" of stitching back our birth-seperated muscles, they just sew up what they've cut (not considering that the whole is now weakened by the surgury and could USE the extra stitching!!!). now, i am aware of my abdomin in ways i never was before: i can tell that it is different/changed, that there is stress at the hernia-repair site, and i know that i'm at high risk for re-herniation...not fun...so take it easy on those abs! pay attention to any minute changes! respect what those abs have been through!
and, best of luck to you in alllll your endeavours!
w/ a smile,