During week 27, your baby's nervous system will grow more intricate, and his movements will become more coordinated as his muscles develop. Also developing at this stage is the respiratory system, namely the lungs. The development of a substance known as surfactant lines and coats the airways with a film that increases elasticity. The decrease in surface tension that results from the surfactant development is essential for the baby to begin breathing once they emerge from the womb. Babies born before 35 weeks may not have enough surfactant production to breathe properly outside of the womb. Giving mom an injection of steroids before giving birth can help speed the surfactant development if your doctor anticipates a premature birth.
Another cool thing that happens around this week is the baby will begin to open and close his eyes as he practices blinking. He will become more aware of changes in light through your abdominal wall. This new sense increases the baby's awareness of his surroundings and often results in the development of designated rest and active periods inside the womb in response to the stimuli. However, don't confuse this with a bedtime routine that which baby is unlikely to develop for months outside the womb.
- American Pregnancy Association - Week 27