At pregnancy week 17, fine hair called lanugo is beginning to grow and coat your baby's entire body. These fine hairs will eventually shed close to term.

By now your baby's legs would have had some time to do some catch up growth. They should now be longer than its arms. 

Also, big changes are taking place to your baby's skin at week 17. Layers of fat are gradually being deposited underneath its skin. It will be essential in helping your child maintain the body temperature after birth.

At pregnancy week 17, your baby is starting to respond to external stimuli. Loud noises on the outside could startle your baby and cause it to move. From next week onwards, the magic truly begins. It is then that its little twists and turns translate into actual kicks felt by you.

Ref: M19