Baby’s development in the second trimester

Learn about how your baby’s brain develops and changes each month in the second trimester.

Month 4:

  • Ultrasound can show if it is a boy or girl.
  • Eyelids, eyebrows, eyelashes, nails and hair are formed.
  • Teeth and bones are more solid.
  • Baby can suck their thumb, stretch and make faces.
  • The thinking parts of baby’s brain get bigger.
  • Baby’s brain is forming connections between what they see, feel, taste and think.
  • Baby’s head is about the size of a macadamia nut (around 2.5cm).

Month 5:

  • Mum may feel baby move.
  • Hair begins to grow on baby’s head.
  • By now baby’s brain has made almost a whole lifetime’s supply of neurons.

Month 6:

  • The part of the brain that tells the body to do basic things, like breathe and swallow, is now formed (brainstem). This means baby can start to practise breathing movements.
  • Loud or sudden noises can scare baby because the nervous system is now in place. Baby may react in different ways, like jump in fright, move around lots or be still.
  • Baby’s brain weighs about as much as an apple (around 99 grams).
  • Baby is about as long as a banana (around 22cm).

Read about the third trimester.

Published — 20 February 2019 Last updated — 11 March 2019

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