My wife is 7 weeks pregnant. Last night I gave her benydril and didn't realize she is not suppose to take it in the first trimester. Will the baby be OK?

To answer your question, following is from the E.How website:

Many doctors consider Benadryl to be safe during pregnancy, but they may recommend against taking any medications unless it is absolutely necessary, especially during the first trimester or shortly before delivery. Pregnant women with mild allergies may choose to avoid using Benadryl or other antihistamines just to be on the safe side. Those with severe allergies, especially ones that affect the ability to breathe, may find that they need to continue using Benadryl throughout pregnancy.