“How your baby’s growing:
Your baby’s growing steadily, having gained about 4 ounces since last week. That puts him at just over a pound. Since he’s almost a foot long, he cuts a pretty lean figure at this point, but his body is filling out proportionally and he’ll soon start to plump up. His brain is also growing quickly now, and his taste buds are continuing to develop. His lungs are developing “branches” of the respiratory “tree” as well as cells that produce surfactant, a substance that will help his air sacs inflate once he hits the outside world. His skin is still thin and translucent, but that will start to change soon. In the past few weeks, the top of your uterus has risen above your belly button and is now about the size of a soccer ball.”
One thing it doesn’t mention is that 24 weeks hits Viability Day: This just means that if for some awful reason i had to have the baby now, the doctors would at least try to save it, whereas before there wouldn’t be much point. i found this chart online that actually shows chances by week.