I was convinced i was having twins after what we now call 'the egg incident'. Never even seen one before but my OH broke into a box of six eggs to make an omlette, and first 2 were double yolks (two full yellow yolks from one egg shell), then a few days later we had the rest, 3 more! 5 out of the 6 were all double yolks!! I've never even seen one before and apparently they are rare. However after scan i am definitely just having the one!!
The scan appointments are fairly quick once you are in around 15-20 mins of on screen time! Sometimes they take blood afterwards depends on what tests you have done when and where in your area.
How clear they are depends on how well your baby is lying and actually how far along you are at your 12 weeks scan (i.e. if you are actually 12 weeks or earlier without realising). Many poeple are told to have a full bladder before hand as this pushes everything up towards your tummy and makes it clearer. Luckily mine was very clear, see my piccie in my ticker below!!
Good luck you'll love it!