Is it safe to take oseltamivir while pregnant or nursing?

Yes and no. If a pregnant woman is infected by influenza virus, it's ok to take tamiflu (oseltamivir). However, if she is nursing, it's recommended to continue the treatment but express the breast milk and bottle feed with formula temporary.
Yes. This is the generic name for tamiflu (oseltamivir). Having the flu and its complications during pregnancy is much more dangerous than the very small risk of taking a limited course of this medication to either treat or prevent influenza when exposed. The CDC says that if breastfeeding, you can continue to do so.