Accutane. An acne treatment containing synthetic vitamin A, Accutane is linked to birth defects, including mental retardation. Because injury can happen in the first few weeks of pregnancy -- often before you know you're pregnant -- you may want to stop using Accutane or ask your doctor for a safer alternative before trying to conceive.

Antibiotics By altering cervical mucus patterns, antibiotics sometimes throw off ovulation while you're taking them. Studies have yet to definitively show, however, whether it's the antibiotics that temporarily squelch fertility or the illness being treated.

Antidepressants. Not only can depression drugs scramble your menstrual cycles, temporarily suppressing fertility, but research also indicates that they may boost your baby's risk of birth defects if you use them during pregnancy. For example, monoamine oxidase (MAO) inhibitors such as phenelzine (Nardil) and tranylcypromine (Parnate) have been shown to cause an increased risk of brith defects when taken during the first 3 months of pregnancy. Since you don't always know you're pregnant right away, consider weaning yourself off antidepressants or finding a safer alternative well before you conceive.

Antianxiety drugs. It is unclear how drugs such as diazepam (Valium) and alprazolam (Xanax) affect fertility, but like some antidepressants, their use has been found to cause an increased risk of birth defects during the first trimester. For this reason, it's wise to avoid taking them, if possible, when you're trying to get pregnant.