Week 25 marks somewhat of a milestone for baby; while he is too young to be born, if for some reason he comes after the 25th week he has a higher likelihood of survival than at any week prior. He would need to remain in the hospital under critical care, but a higher percentage of babies in recent years have survived after making it to the 25-week mark.
At this stage, your baby measures about 10 inches from head to bottom and weighs on average about 2 pounds. He is now practicing many of the functions he will need after he is born like potentially opening his eyelids, opening and closing his mouth, ingesting amniotic fluid, and forming his first bowel movement, or meconium. While his lungs and bowels are immature, and he can't breathe on his own, he is going through the motions to prepare for life on the outside. His ability to see, hear, smell, and taste are all growing stronger every day.
Small capillaries are forming under the skin, so your baby is looking a little pinker and thanks to a little bit of fat he is starting to look more like a tiny human every day. Similar blood vessels are forming in his lungs as well helping the lungs to develop surfactant (a substance that helps them expand with oxygen) which he will need to breathe when he makes it to the outside.
- American Pregnancy Association - Week 25