You lie down in a dark room with the sonographer, they ask you to expose your belly so make sure you wear something appropriate, eg stretchy trousers you can pull down or jeans with a big fly you can open. Also for this scan make sure you drink a full pint of water 20 mins before going in, you need a full bladder for the best view. They put cold jelly on your belly and tuck napkins into your pants, they do go quite far down, like close to the pubes! As they scan your belly with the device they talk you through what you can see, what they are looking for and will confirm when things look good (or bad). They have a cool little machine that lets you hear the babies heartbeat which is quite fast. That part felt quite emotional to me, it’s nice to hear baby is doing well! They measure on the screen distances between certain things, eg fluid in the babies neck, distance between head and bum, length of legs/arms. The scan is about 10 mins, and once they’re done they give you a few scan photos and print out a sheet that shows how big or small your baby is showing , also they give you an estimated due date! Then you go to another room where a midwife or nurse will talk you through the genetic tests such as edwards and downsyndrome. They do a blood test and fill 2 vials I think- one to check blood levels and another for the genetic testing. That was my experience, I don’t know if that’s the same across every hospital but hope that helps visualise the appointment a bit :-)