Week number

Average weight

Average length

Notes

Week 10

2g

22-30mm

The feet are around 2mm long. Body muscles are almost developed. Ears and nose can now be seen. Starts to move around although too small to feel it.

Week 11

5g

35mm

Taste buds start to develop as well as tooth buds. The heart is almost completely developed and the brain is growing fast. Can stick out tongue and suck.

Week 12

20g

6cm

The feet are around 1cm long. Fingernails and toenails start to appear. Can suck thumb and get hiccups. Heart rate can be up to 160 a minute which is double that of a healthy adult.

Week 13

25g

8cm

Can open and close its mouth. Bone starts to replace cartilage, and ribs begin to appear. The unique fingerprint is already developed.

Week 14

45g

9cm

Ears are fully developed. First hair – head and eyebrow hair develop. Eyes move towards the centre of the face.

Week 15

75g

10cm

Taste buds are now fully developed. Can move arms and make a fist. Legs longer than arms and body now larger than head.

Week 16

100g

12cm

Baby hears external voices, sleeps and dreams. Grasps with hands and can kick. Facial muscles are more developed so first expressions appear like frowning.

Week 17

150g

14cm

Retina is now sensitive to light.

Week 18

200g

15cm

Recognisable active and resting periods now. Can hear external sounds and be startled by loud noises.

Week 19

250g

17cm

Scalp hair has sprouted and continues to grow.

Week 20

310g

17cm

Can recognise the mother’s voice. Skin is getting thicker. Senses start to develop at this time with specialised areas of the brain for each sense.

Week 21

360g

27cm head to heel

The bone marrow starts to make blood cells. Weight is steadily gained.

Week 22

450g

28cm

Regular sleeping and waking periods and mother’s movements can wake the baby. Baby reacts to loud noises.

Week 23

550g

28cm

Baby can successfully suck. Eyebrows are now visible and skin pigment is forming.

Week 24

600g

30cm

Eyelids now clearly visible. Baby can react to strong or bitter flavours eaten by the mother.

Week 25

690g

34cm

Hands now fully developed and dexterity improving. Brain growing fast. Baby touches hands to face, hand to hand and foot to leg.

Week 26

760g

35.5cm

Baby’s eyes start to open around this time. Feet now around 5cm long.

Week 27

875g

36.5cm

Eyes can now open, close and blink. Head now over 7cm diameter.

Week 28

1000g

37.5cm

Milk teeth start developing under the gums. Eyes start to move in the sockets. Feet around 5.5cm long.

Week 29

1150g

38.5cm

Can respond to pain. The brain is developing millions of neurons.

Week 30

1400g

40cm

The baby can now control its own body temperature. Wrinkled skin starts to smooth out.

Week 31

1600g

42cm

Eyes now respond to light and darkness.

Week 32

1800g

43cm

The baby sleeps most of the day at this stage. Toenails and fingernails are now completely formed.

Week 33

2000g

44cm

Head diameter is now around 8.5cm

Week 34

2400g

46cm

Fat is building up, plumping out the arms and legs.

Week 35

2700g

47cm

Lungs are almost fully developed.

Week 36

2700g

48cm

Week 37

3000g

50cm

The baby is growing rapidly. Head diameter is now on average over 9cm.

Week 38

3400g

51cm

Development is now complete. The baby continues to gain weight.

Week 39

3420g

51cm

Generally now in the final birth position.

Week 40

3500g

51cm

Head around 10cm diameter.