Did You Know?

In Italy, it is considered lucky for people to touch a pregnant woman's stomach.

40 weeks is the average time it takes for your unborn baby to grow from the size of a tiny dot to a complex human being. We have put together a week-by-week guide, which takes you through each stage of your baby's development, explaining how each of the organs grow and how your baby is experiencing the world.

0 - 4 Weeks
Once conception takes place, the egg and sperm multiply into a cluster of cells (blastocyst). This will then travel along one of the fallopian tubes to the uterus (womb) where it will float freely for a few days before embedding itself in the wall of the uterus.

There are around 150 cells in the blastocyst when it implants. Three layers are formed and will later become different parts of the body - one will become organs like the liver and pancreas, another will develop into the skeleton, and the third will provide the skin.

Your baby is around the size of a pinhead.

5 - 8 Weeks
Your baby already has a heart beating at 140-150 beats per minute and circulation is beginning to function.

Did You Know?

By week eight, the outline of your unborn baby's face has formed and she now measures about 1cm long.

The cells have now multiplied to become an embryo with a face and limbs. A basic spine starts to form, and the brain develops two lobes - by the end of the month, it is almost fully developed.

The major organs develop as well as tiny details such as tear ducts. The skin starts to split into its two layers and hair begins to grow, making downy skin. The mouth and jaw form along with 10 dental buds, ears, nose and eyes, which are sealed by eyelids for now, but already with some colour. The first muscles form and by the end of the month your baby makes it's first flutters of life.

Your baby weighs about 3g (0.1oz) and is now about 3cm (1in) long.

9 - 13 Weeks

Did You Know?

At nine weeks, your unborn baby's eyes are formed and already show traces of the colour they will be after the birth.

The placenta takes over as his support system, feeding him oxygen and nutrients vital for growth. Your baby takes on the shape of a baby with a rounded head, which makes up one third of his body length. It's a time of fast brain growth with a quarter of a million neurons (brain nerves) growing per minute in pregnancy. The first bone tissue and ribs appear, and his primitive tail is absorbed back into the spine.

Ovaries or testicles have formed and you can tell the sex in an ultrasound scan. By the 13th week, the major organs have formed and your baby is relatively safe from congenital abnormalities.

Your baby exercises the diaphram by starting to hiccup.

Your baby now weighs about 18g (0.6oz) and will be around 7cm (2.5in) long.

14 - 18 Weeks
The placenta is now producing hormones and other substances, which are necessary for your baby's growth and development. Your unborn baby is still small enough to swim around the uterus and take up any position he wants. Your baby also responds to touch and may wriggle when your midwife or doctor gently presses your abdomen.

Did You Know?

By week 15, your unborn baby can suck her thumb and grasp her umbilical cord.

The nervous system is growing, made up of neurons (brain nerves) and glial cells. Glial cells are the glue, which bonds the whole nervous system together, giving the brain form and structure. Your baby's bones and lungs start to develop. Your baby will practise breathing movements, taking in and expelling amniotic fluid instead of air.

Your unborn baby will start practising to use the lip muscles needed for the sucking reflex after birth for feeding. The first facial expressions begin, screwing the face up and wrinkling the forehead.

Your baby now weighs about 135g (5oz) and will be about 16cm (7in) long.

19 - 23 Weeks
The first sense to develop is touch and ultrasound pictures show that babies spend time patting and stroking the amniotic membrane, the umbilical cord and themselves. As ears develop, your baby will be more aware of sounds - research from Keele and Bath Universities suggests newborns recognise music played to them from this time, while a Venezuelan study suggests parents who talk to their babies during pregnancy have alert, sociable children at birth.

Did You Know?

The survival rate for premature babies born between 22 and 32 weeks is more than 80% and improving all the time.

Milk teeth are developed in the gums and buds form for permanent teeth. The taste buds now begin to develop - research from the 1930s by Karl Desnoo at the University of Philadelphia, US, showed that unborn babies prefer sweet to non-sweetened fluid.

Your baby will undergo a period of rapid growth as the body, arms and legs lengthen. Eyebrows and eyelashes start to grow and the head hair takes on texture and colour - lanugo (body hair that may appear on the back and shoulders after birth but soon disappears) also starts to grow.

Your baby now weighs 340g (12oz) and will be 26cm (10in) long.

24 - 28 Weeks
With the help of specialist medical care to help your baby breathe, your baby would have a good chance of survival if born at 28 weeks.

Did You Know?

By 28 weeks, your unborn baby is able to see bright lights through the skin of your abdomen.

Around the end of this month, your baby's eyelids will unseal and the eyes will open as the senses develop. Your baby will be able to see bright light as a reddish glow through the skin of your abdomen, will be able to hear very well and can more than likely be able to recognise the mother's and father's voice. Research shows that some babies prefer plain breast milk, while others like it with a hint of garlic or spices depending on what the mother eats during pregnancy. It is believed that fear can also be experienced as studies in Italy during 1980 following an earthquake showed that babies of mums who had been frightened showed an abnormally high rate of movement for several hours afterwards.

Brainwave patterns are now more sophisticated and are similar to those of a newborn. The brain cells develop a protective fatty sheath (myelination), which is vital for transmitting messages quickly and so speeding up thought processes.

Your baby now weighs 500g (1lb 2oz) and will be 33cm (13in) long.

29 - 32 Weeks
Your baby swallows amniotic fluid and excretes it as urine (about 568ml (1 pint) every day). The urine is however sterile and does not foul the surrounding waters.

Your baby will now be quite large and may settle into a position, although will probably not stay in it. The organs are almost fully mature except the lungs, which need to make more surfactant, a fluid, which stops the lungs sticking together and collapsing at birth.

The lanugo starts to drop off but the head hair continues to grow and the eyebrows and eyelashes will be fully-grown. The eyes will dilate and contract in response to bright light and your baby will practise blinking. In boys, testes will descend at this time.

Your baby will start to lay down fat supplies (especially protective 'brown fat') to help regulate the body temperature at birth.

Your baby now weighs around 1.6kg (3lb 8oz) and will be 40cm (16in) long.

33 - 36 Weeks
Your baby's rest and movement periods will be more noticeable now the nervous system is maturer. They can be divided into four phases...

1. Active sleep with REM (rapid eye movements).
2. Quiet sleep when the baby does not move.
3. Being quietly awake.
4. Actively awake.

Once your baby is born, one new phase is added - crying!

For first time mothers, the baby's head may have engaged firmly into the cervix (neck of the uterus) ready for delivery. This is not always the case for second time mothers as the baby has more space.

By 36 weeks is almost fully mature. The vernix, which protects his skin is thicker, the fingernails are grown but the toenails are not.

Your baby will now weigh approximately 2.5kg (5.5lb) and will be around 45cm long (18in).

36 - 40 Weeks
Your baby is now fully developed and is simply gaining in weight and strength. The powerful sucking muscles get much plumper ready for feeding after birth.

Your baby's eyes will be blue when born and can take up to a year to settle into their natural colour and the fingernails will be long and sharp.

The only organs left to fully mature are the lungs, which is helped by the hormone cortisol. Birth is determined by your baby's maturity, as once fully mature, hormones will be produced which will induce labour. The intestine is filled with meconium, which will be your baby's first bowel movement. Your baby's position will be legs curled into the chest and arms hugged to the side. This position will normally be assumed after birth.

Your baby can weigh anything from 2.75kg to 4.5kg (6lb - 10lb) and will be between 45cm and 60cm in length (18in - 24in).