Can using tazorac gel for acne affect child birth/lead to birth defects?

Hard to be sure: While I know of no clear research on the subject there are some basics that make this unlikely. To affect the formation of a fetus a drug must enter the bloodstream in a quantity that can reach the blood supplying the fetus. Creams/lotions applied do not penetrate deeply enough for drug entry into the blood in significant amounts. That said, the manufacturers of the drug will say to avoid it.