I had this last pg, midwife discovered it about 24 weeks when I showed her the weird bulgy thing that happened when I sat up! She referred me to a physio who taught me a few exercises, but they continued to seperate anyway. Didn't affect labour at all, but they gave me some tubigrip stuff afterwards to wear, because you get a bit of a "it's all hanging out" sensation. Six weeks after the birth I was referred by the physio to a "tummy toning" class where they just went through the exercises again. They said they will close up eventually anyway, but the exercises help it happen quicker. I worked on mine, but as soon as I was pg again, they opened up like a zipper!

Only advice I would give is to be careful getting up out of bed etc and roll on your side to get up, rather than sit straight up.