Pregnancy can cause the blood vessels in your nose to expand, and your increased blood supply puts more pressure on those vessels, causing them to rupture more easily n such! But it's normal during pregnancy and nothing to be concerned about :)
I never had one before I got pregnant! And once I had one I freaked out and read all about it lol!
I've been getting tons of nosebleeds since I found out, but I was no stranger to nosebleeds to begin with