Is it safe to use fertilizer in my yard when i'm pregnant?

Probably: Organic fertilizers, nitrogen based formulas, should be safe, especially later in pregnancy. Pesticides of any kind should be avoided.

I wouldn't : I would avoid fertilizer exposure, if possible. Certain fertilizers have been known to be "endocrine disrupters" and it would be wise to avoid them in pregnancy if possible.

Depends: It depends on the fertilizer and how you handle it. Some fertilizers can be dangerous to the fetus. See http://www.Ncbi.Nlm.Nih.Gov/pubmed/8056207.