I have 4 (?) standard fillings, which I'm assuming have mercury in them. I just had my mercury levels tested for a Greenpeace study and there wasn't any mercury detected. To keep your levels low, be careful of the fish you eat. To find specific fish advisories in your state or region, go to: http://www.epa.gov/waterscience/fish
My first baby wasn't perfect. He was born with a severe cleft lip and palate. I blame my being a smoker before finding out I was pregnant, but really that was just one factor out of many environmental factors that I can't possibly know or determine. If you are worried, make sure you're taking a good amount of folic acid. They recommend 1 mg for pregnant women. Because my first child was born with the cleft, I'm taking at least 4 mg of folic acid a day, and 8 on the days that I can stomach it (I've been nauseous a lot lately so my vitamin taking has suffered).