I was nervous as well unfortunately it can happen... the chances go down to less then 1 percent after the 12th week and they find a heartbeat with a doppler externally... unfortunately at the 4th week the chances of miscarriage is over 30% u can actually Google it good luck to you I'm sure everything will turn out just fine!!! As a lady told me if u do miscarry that means something was wrong with the growing fetus and the body has no choice but to abort the pregnancy rather it just be implantation didn't occur properly or just something else went wrong babies are a true miracle so many things have to go right it's hard to believe with all the people we have in the world I've just also known lots of ppl to misscarry as u I still worry I am just in my 18th week the worrying never stops!