I'm assuming you mean for labor and delivery?
Epidurals are diffused across cell membranes. This means that the medication can migrate to the baby over time depending on how long it's in place before delivery. The same goes from spinal anesthesia, which is sometimes used (though more commonly in c-sections). The alternative to regional anesthesia is IV drugs which go into your bloodstream and reach the baby through the placenta almost immediately. They have more of a sedative effect of the fetus than does the epidural, though there are many reasons that women avoid getting epidurals and spinals as well. IV drugs that are usually used are Demerol and Stadol. You should know that they don't completely remove the pain for every woman (nor does regional anesthesia) and they can also alter how you feel, for instance they can make you very groggy and sometimes nauseous. If you go to babycenter.com you can read plenty about the different types of pain relief for labor and delivery.