Week By Week Development

Every baby is unique and develops differently -- even in utero. The week by week development guide is a rough guide to new born development, preterm and term.

Week 23

By this week baby measures over 28cm (11 inches) and weighs a little over 500 grams (1 pound)
The eyebrows are visible
Skin is fragile, quite red and wrinkled
Bones located in the middle ear begin to harden
Lungs extremely immature and baby is practicing "breathing"—sucking amniotic fluid it in and out of their lungs
Baby is continuing to fill out and look more proportioned like a newborn
Baby can hear loud noises in the womb and may move around a bit more if you are in an environment where loud noises are quite common.

Week 24

By this week baby measures 30cm (12 inches) and weighs about than 600 grams (1.3 pounds)
Eyelids are fused and can be seen clearly. They may even have a few eyelashes
The lungs are very immature but continue to develop and begin to produce surfactant which helps the air sacs inflate easily
The body begins to fill out with his appearance increasingly becoming more like a newborn
Taste buds begin to form
Little creases have appeared on his palms.
Sweat glands begin to form in the skin.
Inner ear is fully developed and sense of balance is working
If born at this stage of pregnancy baby is officially considered viable and may survive premature birth

Week 25

Baby measures 34cm (13.5 inches) and weighs almost 700 grams (1.5 pounds)
Bones are becoming solid, hands are now fully developed.
The brain is growing rapidly, the brain cells are starting to mature.
The sexual organs are fully developed
Baby's nostrils, which have been plugged up until now, begin to open
Baby's hands are now fully developed
The structures of the spine are starting to form and will be made up of 150 joints, 33 rings and some 1,000 ligaments.
Capillaries are forming which are the tiny blood vessels that move blood from the heart to tissues in the body
Swallowing reflexes are developing
Baby is sensitive to touch, particularly around the mouth
Lungs are very immature and continue to develop, if born baby will require breathing support.

Week 26

Baby measures 35.5cm (14 inches) long and weighs a little more than 760 grams (1.7 pounds)
Baby is starting to add fat to their bones
Nerve pathways in baby's ears continue to develop and responses to sound are more consistent
Eyes begin to open
Baby is covered with a downy coat of hair called lanugo
The feet are 5cm (2 inches) long
Hands are very active and baby may be able to get a thumb into their mouth
Foetal brain scan will show response to touch
Brain growth continues with brain wave activity for the auditory and visual systems detectable
The retina is formed and baby's eyes are now fully developed.

Week 27

Baby now measures 36.5cm (14.5 incehs) in length, weighs about 875 grams and is perfectly formed all be it on the small side
The head is 7cm (2.5 inches) in diameter.
Eyes are now longer fused and can open and close
Baby now has eyebrows and eyelashes
The retina begins to mature and will allow baby’s eyes to receive light and transmit the information it is receiving to the brain
Baby sleeps and wakes at regular intervals
Baby makes breathing movements, however if born, may need equipment to help with breathing

Week 28

37.5cm (14.8 inches) in length and weight has increased to 1000 grams (2.2 pounds).
The feet are 5.5cm (2 inches) long
The hair on the head is now clearly visible
Brain waves show rapid eye movement (REM) sleep and eyes are starting to move in their sockets
Fingernails are well formed
Up until now if you were to look at the brain it would appear smooth. By about 28 weeks, the brain starts to mature and form grooves/folds

Week 29

Baby is now about 38.5cm (15 inches) long and weighs 1150 grams (2 ½ pounds).
Skin is looking less wrinkled as weight is gained
Baby’s head is growing and the brain is busy maturing and developing billions of neurons
Branches of lungs are quite developed now. Some babies may breathe without support, however pauses in breathing are common and intermittent breathing support/extra oxygen may be required
The milk teeth have developed under the gums
Baby's muscles and lungs are continuing to mature
Baby may be able to taste
In boys, testicles are making their way down from near the kidneys through the groin to the scrotum. In girls, the clitoris is relatively prominent because it's not yet covered by the small labia

Week 30

Length is now 40cm (16 inches) and baby now weighs 1.4 kg (3 pounds).
Digestive tract and lungs are almost fully developed
Baby can distinguish from light and dark and may turn their head towards a continuous, bright light shining from the outside.
Baby is getting fatter and beginning to control its own body temperature.
Eyebrows and eyelashes are fully developed, and hair on the head is getting thicker.
Wrinkled skin is becoming smoother now
Bone marrow is completely responsible for red blood cell production

Week 31

Baby measures around 42cm (16.5 inches) from head to heel and weighs 1.6kg (3.5 pounds).
Organs continue to mature and baby is passing water from their bladder
A loud noise close by may cause baby to jump
Lungs may be mature enough for baby to breathe without assistance, although some may require extra oxygen
Baby is busy growing layers of fat and muscle mass
Baby can now process information from all five senses

Week 32

Baby is 43cm (17 inches) long and weighs 1.8kg (4 pounds)
The diameter of the head is around 10cm (4 inches)
Under the skin the fat layer is getting thicker
Fingernails are completely formed and grown long enough to reach the tip of their fingers
Baby sleeps most of the day and some will have settled into the head down position ready for delivery
Baby may be smiling and sticking out their tongue
Although lungs won't be fully developed until just before birth, baby continues to inhale amniotic fluid to practise their breathing

Week 33

By this week baby is around 44cm (17.5 inches) in length and an amazing now 2kg (4.4 pounds).
Hairy lanugo is disappearing
Baby's respiratory system is almost completely mature
Baby is drinking approximately 450mls of amniotic fluid a day and urinating the same
Baby's brain is busy maturing and increasing in size
Skin will begin to change from red to pink as fat begins to gather under its surface
Bones in baby’s skull are still quite pliable and not yet fused while the bones in the rest of the body are hardening
Pupils will constrict and dilate in response to light

Week 34

Baby now is approximately 46cm (18 inches) long and weighs about 2400 grams (5.25 pounds)
Arms and legs continue to fill out as a result of fat development
Eyes opened when awake and closed when sleeping
Baby is coated in thick, white substance called vernix
Lanugo is almost completely gone
Baby begins to develop their own immune system
Toenails reach toe tips

Week 35

Baby is ,measuring about 47cm (18.5 inches) and weighs almost 2.7kg (5.5 pounds)
Beginning to look more rounded and pink in colour
Has a fully developed pair of kidneys and liver has begun processing waste products
Reflexes are coordinated
Lungs are almost fully developed
Suckle reflexes should be well developed. If born at 35 weeks most babies will be able to breastfeed with little trouble
Baby will begin to develop daily activity cycles

Week 36

Baby measures about 48cm (19 inches) long and weights around 2.7 kg (6 pounds) and still gaining weight – approx 28 grams a day,
Body is becoming chubby as fat layers build and creases in the neck and wrists are forming
Gums are firm with ridges that look a little like teeth
By the end of this week, your pregnancy will be full-term

Week 37

Typically, baby now measures 50cm (19.5 inches) and weighs in at 3kg (7 pounds)
Baby is growing rapidly and continues to gain approx 28 grams per day
Many babies now have a full head of hair
Babies born at 37 weeks are considered full term, before 37 weeks premature and after 42 weeks post term
Baby is busy practising their breathing, sleeping, gazing and sucking

Week 38

Baby is now about 51cm (20 inches) in lnegth and 3.4kg (7.5 pounds).
Development is complete and baby continues to gain weight
The wrinkled skin is becoming 'baby' smooth
The baby may have reached its final birth position
Most babies are born head first with only about 3 percent coming out feet first
Baby will swallow the lanugo and exterior coating, and store them in their bowels. This will become a blackish tar like waste called meconium which is eliminated shortly after birth

Week 39

The average baby is about 51cm (20 inches) and weighs approximately 3.4kg (7.5 pounds)
The baby has reached its final birth position.
Baby’s head is about 10cm (4 inches) in diameter
Most of the downy coating of lanugo has disappeared, though you may notice some on baby’s shoulders, back and arms after their birth. This will vanish on it’s own in time

Week 40

By week 40 baby is now around 51cm (20 inches) in length and weighs around 3.5kg (7.5 pounds).
Internal organs are fully matured and ready for life outside the womb
Baby’s eyes are well formed, but the nerves inside his eye will continue to develop in the first weeks after birth
The bones of baby's head are soft and pliable to ease the process of delivery through the birth canal
At birth your baby has a total of 300 bones and some of which will fuse together later
Baby's genitals (scrotum in boys and labia in girls), and even his or her breasts, may appear enlarged at birth, this is completely normal