yeah, it happened to me 2, i had what they called a missed abortion. my fetus stopped growing the heartbeat faded and the baby slipped out of place,but my body dint recognize it,so i started cramping and spotting,until i went for that vaginal scan thats when they realized everything was rong, so they gave me some pills which aborted the baby and now we trying again, i hope nothing lik this happens to yours!
Unfortunately the situation that you stated is exactly what happened to me. I went in for my first u/s and they measured me at 6w4d. We heard the heartbeat and even saw our lil' bean. We were told that everything looked wonderful and that it was safe to spread the news. Well two and half weeks later I started spotting which turned into bleeding. I went to dr. and learned that the baby stopped growing at 7w4d just one week after we saw a strong heartbeat. About the twins situation I have no idea about that.
I'm sorry to give bad news, but I wanted you to be aware that there is a possibility of such a thing happening. I hope my situation is not something that happens to you. Best of luck!
Something like less than a 5% chance after heartbeat is seen, and next to no chance of missing a twin. Why do you suspect twins?