Honestly, I wouldn't have wanted to breath in paint fumes when I was preggers... But then again, I am allergic to latex... which includes latex paint. Paint fumes in general give me respiratory distress and headaches. But, perhaps I'm more sensitive to it anyway?
You probably need to strip the wood and do a light sanding of all sides/parts of the crib, as new paint will not stick to varnished wood (and you don't want the paint flaking off or posing a risk of being ingested when the baby is grabbing the rails and is more mobile in the crib). (Wear a mask so you don't breathe in the wood & varnish particles! Yuck...)
You can get the repainting steps from: http://www.helium.com/items/346774-tips-for-painting-old-...
(And admittedly, maybe I'm just lazy but we were given a crib... It doesn't match. Its fine. No one from a baby magazine was going to take pictures of her room anyway. I figure we will devote all the time, effort and money to making a cutesy girl room when she gets her real bedroom furniture. Her baby furniture is only gonna be used for 1-3 years anyway... not worth it to me...)