Week 25 marks somewhat of a milestone for your baby; while he is too young to be born if he should come after the 25th week, he has a higher likelihood of survival than 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 an average of about 2 pounds. He is now practicing many 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 independently, he is going through the motions to prepare for life on the outside. His ability to see, hear, smell, and taste grows 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, helping the lungs 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