It cud be the procudures that you had done, all that stress cud have caused you to lose them.
But apart from that studies have shown that most women who have first time multiple pregnancies usually do miscarry. I don't really know why.
I was pregnant witha twin last december and I lost them too ant 11 weeks, and I was so busy planning my daughter's 10 b'day party and just stressing the whole damn day making sure that all was going well, just basically running up and down. I was out of bed from 4:30 that morning and never lied down again until 10 that night. Iplayed every game at the party. When I took my shower I saw this brownish discharge. I knew something had to be wrong becuz I wasn't there the day before or early that morning. I had an ultrascan the next day and they weer fine, went back the following week and they were dead.
I just think that our bodes react to stress and carryin two babies has to be more of a strain on our bodies than one and if they share the same sac or the same cord, as in my case, chances are that if one is affected it will surely take the other one with it.