What are somethings my girlfriend should stay away from while she's pregnant?

Preterm birth: She should avoid smoking, alcohol and drug use, excessive work hours, heavy lifting and poor work conditions, extremes of weight, and psychological stress. These may result in preterm birth or her "water breaking" early. It is also important that she avoids medications which may cause birth defects. Sexual intercourse is ok. I don't know of any specific dietary restrictions.

Long talk needed: There are books written on this question. The obvious chemicals to avoid are chemicals that can damage dna. Certain secosteriods such as vitamin a will change the number of toes or fingers if you take in too high a dose, or to low a level during early pregnancy. Betacaroteen and zinc can be given to help form vitamin a safely. A good prenatal vitamin( in most people)fills in vitamin needs of fetus.