Babies in the womb are quite safe, but its always best to be checked out to be on the safe side. Good to hear the fall didn't hurt too much other than the bum.
Note on falling but not with child, I was about 3 weeks out of the hospital with my last child, went out to take a baby break and walk the dog. For some reason he thought it would be best to chase a squirrel, while on the leash with me. We both ended up in a ditch, the little rodent got away and I came in the house with dirt all over me, told husband baby break wasn't fun.