Hmm.. every kind. Nail polish doesn't seep into your blood stream anymore than say soaps, makeup, shampoos, etc do..
If anything, I'd be more concerned about cleaning products and even air sprays (alcohol-ridden room deodorizers) -- even breathing the fumes of Lisol and Pinesol can get into your bloodstream quicker than nail polish.
BTW: They do sell "natural" nail polish at different beauty stores if it bothers you so. But I've never known of a pregnancy complication because of nail polish, the fumes of it are much less potent than cleaning products (unless you sniff it for hours or some such.) I think you're okay. : )