I had mine at 18 weeks as was about to go on holiday...There are a lot of things! Fingers and toes were counted, length of limbs, complete diaphragm (between abdomen and chest) bladder, kidneys, flow through the heart (looking for abnormal connections), palate (looking for cleft palate) flow of fluid through the brain, lenses within the eyes and other things (rechecking nasal bone length). also looked at my placenta, umbilical cord and my ovaries too. I'm not sure they check sex routinely unless you ask.
They also check heart and brain, (blood flow and vessels) position of baby and of your placenta, amniotic fluid, babies kidneys...there's like 22 things.
Sex,size of femur,skull & spine,fluid in sac, and I believe there one or two more things they look for but can't remember