The immune system matures with antibodies from you. The fetus is preparing for the outside world.
Week 35 - Preparation for Birth
Week 25 - Brain Growth Spurt
Week 14 - Bones Harden
Week 31 - Bone Strengthening
Week 13 - Rapid Growth Phase
Week 7 - Facial Features Form
Week 8 - Major Organs Develop
Week 38 - Organ Maturation