Here's what's going on with baby at 12 weeks:
Even though your little Einstein’s body is still growing quite rapidly (it's 2 inches long right now), the overall super-speedy growth of their amazing brain continues to leave the head proportionately larger than the body— and is actually slightly more than one third of their total body mass! The head and neck are still straightening at this point as can be seen by their little chin lifting off of the chest. Your baby is also actively rehearsing “breathing” by using amniotic fluid to prepare the lungs for future air respiration.
The big news: your little pooper is now officially going to need diapers!