Apparently, clear polycarbonate bottles can give off a substance that's harmful to fetuses. So if you're a pregnant woman, you should not reuse bottles that have a #7 on the bottom inside the recycling logo. You should likewise not reuse #1 bottles (the kind most bottled water comes in), as they can give off a suspected carcinogen. I've been reusing those a lot. Oh well. :P
So check that plastic type: #2, #4, and #5 bottles are safe to reuse, according to the article.
And this has been a klog public service announcement.