Percocet is in the FDA pregnancy category C. Which means it has no known side effects to an unborn fetus. But, that's because it hasn't been tested on unborn fetuses (because it obviously can't be). However, I believe when they put a drug in this category it means that many pregnant women have taken it without any ill effects to their babies. I had surgery at 7 months pregnant and took percocet for the pain after. My little guy is now 3 months old and very healthy. However, I don't know if being in the third trimester as opposed to the 1st or 2nd has any less effect on the baby since it will obviously be more developed in the last trimester.