I haven't posted one of these in a while!! here's the most recent stage my babies are at. It should be about the same for twins, just picture 2 of them in there :)
here's the description from the website http://www.wpclinic.org/parenting/fetal-development/third-trimester/
There is a rapid increase in the amount of body fat the fetus has. Rhythmic breathing occurs, but the lungs are not yet mature. The fetus sleeps 90-95% of the day. At this point there the survival rate is above 95% if the baby is born.
And here is a picture of what twins looked like a week ago,
At 28 weeks your twins will have grown to about 15 inches/ 38cm from top to toe (10 inches/ 25.5 centimetres from crown to rump) and will weigh nearly 2 lb /875g each.
Their eyes open and close, they sleep and wake at regular intervals and they may suck a finger or thumb.
Your twins' brain growth is very rapid this month. The characteristic grooves on the brain's surface start to appear and more brain tissue develops. Nearly all fetuses react to sound by the end of the seventh month.
At about this time, your twins can open their eyes and turn their heads in utero if they notice a continuous, bright light shining from the outside. Their fat layers are forming. In boys, testicles descend from near the kidneys through the groin en route to the scrotum. In girls, the clitoris is relatively prominent because it's not yet covered by the still-small labia. These will grow to cover it in the last few weeks before birth.
Their skeletons are hardening even more. While your twins may soon slow down growing in length, they will continue to gain weight until they are born.
A pint and a half/around a litre of amniotic fluid now surrounds each of your twins, but that volume decreases as they gets bigger and have less room in your uterus.