well i am glad you have found out already, If only I had come apond the post earlier as with my 3rd they heard a slight eco ( which can be the twin sitting behind the 1st bub ) but I too only had one... It a stange feeling isnt... Not really wanting it to be twins but by the time you find out its only one it kinda feels like you lost one as you have just got used to the idea there might be 2 in there... Wishing you a happy and healthy Pregnancy...