Is it legal to be fired from a job if for being that time of month?

This is so embarring and sounds crazy, but I was let go from my job today because on Friday, I had started my monthly cycle and accidentally got blood on a chair, which I cleaned up myself. I work at a day care with children and the director said I put the children's health in jeopardy by not saying anything about it or asking to go home. Well, I didn't say anything because it just happened and almost time for me to be off. Can they just let me go like that? Do I have any legal rights to defend myself on this issue? Please feel free to give me any feedback on this. I feel so awful about it.