Did anyone have a missed twin at 12wk scan?

Hi I'm just curious to see how common it really is for twins to be 'hiding'.

I'm pregnant with my 3rd child and my uterus has been measuring 4 wks ahead all along but twins were never questioned. I had my 12wk scan and they saw one baby and one heart beat, however now i'm coming up to my 20wk scan and my midwife has urged my to get them to have a really REALLY good look for a 2nd baby!!!!!!! 

Surely a sonographer wouldn't miss a 2nd baby? would they??

Oh, and my dates are definitely right, the dating scan matched my own dates to the day.

Thanks

Never heard of it in with the current technology (though my mum was a missed twin back in the day's of no scans) she appeared not long after her sister was born to a shocked mum, midwife & doctor! I would explain your m/w concern and get them to have a really good look! Good luck

Ther was just one phew don't think I could cope with twins!! Thanks