can a twin be hiding in 10 week ultrasound?

Kathleen

My Dr was very quick at 10 weeks...locate baby, measure, see heartbeat, give due date. He set me up for another at 13 weeks. I was comparing this 10 week ultrasound (left) to my last baby (right). Why is there a dark spot on far left of new baby's picture? Hiding twin, ovary, etc? I & others have dreamt I was having twins but I'm so thankful for the one I see! I'd just like thoughts/experience shared. Thanks!