missed miscarriage!!

Ta

how common is a missed miscarriage ? I started spotting brown when I wiped a couple of times Tuesday, Wednesday morning I called my doctor and they told me to come in because they could not tell me either way what it was at this point the spotting had stopped when I wiped. i went in my doctor told me my ultrasound the week before had looked great. I am pregnant with twins and both measured good and the same and had strong heartbeats. he then did my exam and saw the brown discharge I was talking about. he told me it was brown and was old blood but still told me to go on bed rest. my cervix was closed. he also said if it got heavier go straight to the er. since then I have been mainly on bed rest only getting up a few times to get my little boy things but not much even that. the spotting has pretty much stopped except I checked my own cm this morning and there was a slight brown discharge inside me but the past few days nothing when I wipe. i feel like my pregnancy symptoms have lessened though which is another that's really got me worried and upset. my doctor didn't want to do another ultrasound because he had just done one. any advice or words of encouragement would be great thank you so much.