31st weeks
- The fetus reaches a length of about 38–43 cm (15–17 inches).
- The fetus weighs about 1.5 kg (3 lb 0 oz).
- The amount of body fat rapidly increases.
- Rhythmic breathing movements occur, but lungs are not fully mature.
- Thalamic brain connections, which mediate sensory input, form.
- Bones are fully developed, but are still soft and pliable.
- The fetus begins storing a lot of iron, calcium and phosphorus.