Stages Of Fetal Development
The Second Trimester

This time should also be a lot easier for you as a lot of the pregnancy symptoms, such as nausea and tiredness should be wearing off.

So for the next 13 weeks, sit back and enjoy the coming fetal growth and development, and wonder at what is taking place inside your body.

You should also give yourself a pat on the back... Congratulations Mom!

Stages of fetal development - Weeks 14 to 17

Week 14

• Your baby now measures around 9cm long.

• His head may now have a little hair, and he may have eyebrows too.

Week 15

• Baby's skeleton is starting to develop rapidly now as the bones retain more calcium.

• His hair will be getting thicker, and baby's who will have dark hair will start to develop a dark pigment in the hair follicles.

• Your baby may now be as long as 10cm!

Week 16

• The umbilical cord supplies your baby with oxygen as it passes blood through. But your baby is now breathing amniotic fluid, practising this talent for when he reaches the outside world!

• He may now be 16cm long! (That's a lot of growing in one week)

• You baby's legs are now longer his arms (as they should be) and his fingers and toes have tiny nails!

• Baby's inner ear has properly formed at this stage, so he can hear everything! Loud noises may startle him.

• He now has taste buds.

Week 17

• Have you ever heard of brown fat? It's a deposit of fatty tissue. This week that is what your baby is busy doing, building up and storing (laying down) brown fat (especially around the torso). This will help your baby to regulate his temperature once he's born.

• Tiny bones inside your baby's ears are fully developed, he can hear your heart pumping your blood around your body, and even your voice (it all sounds rather strange though, a bit like he has ear muffs on!)

You will soon be able to feel movement, and the stages of fetal development will seem more real.

Stages of fetal development - Weeks 18 to 22

Week 18

• The gender of your baby is now visible for all to see on ultrasound. So long as he's lying in the right position!

• Your baby may be making little movements that you can now feel! If a noise startles him, you might feel him jump.

Week 19

• Your baby could now weigh in at around 1lb (0.5kg) and measures about 18cm from head to rump.

• Baby's nerve connections are developing, and all of the movements that he makes in his watery home are strengthening nerve signals to his muscles.

• Your baby can now suck and grasp, if you were to have an ultrasound you may catch him sucking his thumb!

Week 20

• At approximately 25cm long, your baby is coated in a greasy substance called 'vernix'. This will help to protect his skin while he floats in amniotic fluid. 9 months is a long while to be suspended in fluid!

• You are now passing on immunities to your baby from any viruses that you have had. These will last until your baby is 6 months old.

Most of the fetal growth and development now is just time spent getting bigger and putting on weight.

Week 21

• Your baby will be freely moving around in your uterus now. You should now (or if not now then very soon ) be able to feel his every move. His movements will feels stronger as the coming weeks pass.

• If you can feel your baby, you may start to notice his sleep and waking periods.

• White blood cells are being produced.

• At 21 weeks, your baby now weighs around or just over 0.5kg.

Week 22

• Eyelids and eyebrows are formed, and finger and toenails are now growing well.

• The lines on baby's hands are starting to form.

• Your baby's brain is entering a rapid growth stage.

• Arms and body are much more in proportion to the head.

• If baby is a boy, his testes are now descending into the scrotum.

Remember weekly fetal development will continue right up until you give birth (even if it's only putting on weight!)

Stages of fetal development - Weeks 23 to 26

• Your baby will now be able to recognize your partners voice... So get him to sing!

• His eyes are now formed although they have no colour to them yet.

• Try playing a soothing piece of music every day. Studies show that if your baby is used to a certain piece of music, this can have a calming effect on him once he is born.

• The pancreas is developing, and baby can now produce insulin, which will help with the breakdown of sugars.

Week 24

• Your baby will now weigh around 1.3lb, and be around 30cm long!

• Your baby's heartbeat can now be heard by a fetal doppler, an instrument that your midwife may use to listen to his heart beating (kind of like an upside trumpet!)

• Baby's heartbeat will be around 160 beats per minute! (that's a healthy heartbeat)

• His lungs are continuing to grow, more air sacs are forming with each passing day. The cells are also producing 'surfactant', this essential for helping baby to breathe.

Week 25

Stages of fetal development continue with the build up of fat.

• Your baby is building up fat under the skin, and is now learning to regulate his temperature control.

• Baby is producing red blood cells in his bone marrow.

• Your baby's swallowing reflexes are developing.

• Your baby is learning to use his hands. He can make a fist and and is learning to clasp things (maybe the umbilical cord)

• His spinal structure begins to form, the bones, joints and ligaments of the spine will all protect his spinal cord in the outside world.

Week 26

• As baby lays down more fat under the surface of the skin, the fine network of veins are no longer visible.

• Your baby's eyes are beginning to open, and he will soon start to blink.

• If your were to have a fetal brain scan, your baby would show a response to touch!

• Try shining a light (torch) on your tummy, see if you notice movement as your baby tries to follow the light.

• Your baby may now weigh in at around 2lbs, and has reached a length of approximately 35cm!

And that's it for the stages of fetal development of the second trimester... Congratulations!

If you fancy a peek at the week by week fetal development for the third trimester, then take a look here.

Return from stages of fetal development - first trimester, to the pregnancy page.

Or back to the new baby and beyond homepage.