Antibiotic at birth...?

So my doctor said that when I'm going to give birth she is going to give me an antibiotic to take. I just said ok, and that was the end of the visit. Of course she asked if I had any questions and I said no lol, but now that I'm home I'm wondering what that antibiotic is going to be for. My next appointment isn't for a month, so I'm going to be curious until then. Have any of you ladies had to take an antibiotic when giving birth, if so what was it for???