hmm are your stretch marks white or are they fresh and red ? if they are red i wouls suggest waiting a while .
i have some old ones on the side of my arm and one goes onto my back a little , the shading along my wings went over it and now you cant see it was ever there.
they hurt to go over and swell up afterwards more than other skin but i have never had any problem having a tattoo over them.
some people do get blow outs over stretch marks but i think they really depends on the artist .