I had a fall when preg (in fact overdue) with DD1 10 years ago...managed not to fall on my tum and ended up with grazed knees and hands (happened outside)......went into labour that night and everything was fine with her...a very healthy and unstressed bubs...not trying to frighten you by saying you might go into labour, lol!! As I said I was overdue anyways, but the upshot was she was fine

But if you have any doubts go and see your doc....hope all is well