Development of the Foetus

4-5 Weeks

The fertilized egg is now called an embryo, and is connected to the mother by the umbilical cord. The inner cells split into layers that will become the brain and nervous system, the skin, eyes and ears, the lungs, stomach, gut, heart blood muscles and bones. The first missed period is in the fifth week and already the baby's nervous system is developing. A groove forms in the top layer of cells that then folds up and round to make a hollow tube that will become the baby's brain and spinal cord. It has a head and a heart, plus buds that will grow into arms and legs. The bones and organs are beginning to develop. At 4 weeks it is 5mm long.

6-7 Weeks

The embryo is now called a foetus. The brain is developing and the heart is beginning to beat. The arms and legs are growing, as are the fingers and toes, and the spine is developing. There are lumps where the ears will be. At 7 weeks it is 2 cm long.

8-9 Weeks

The face is forming, the eyes even have some colour, and there is a mouth with a tongue. At 9 weeks it is 17mm long.

10-14 Weeks

The foetus is fully formed with all its organs, muscles, limbs and bones, even its sex organs and it's eyelids. It's heart beats at twice that of an adult and it can move around inside the womb. At 12 weeks it is 6cm long and weighs 10-14g. At 14 weeks it is 56mm long.

15-22 Weeks

The foetus is growing quickly and the head and body are more in proportion. The hair is growing on its head as is the eyebrows and eyelashes. The baby even already has it's own distinctive fingerprint. At 20 weeks the heartbeat can be heard and the foetus weighs about 350-400g. At about 22 weeks the baby is covered in a fine hair called lanugo that we don't know the purpose of, and a white waxy grease called vernix. At 18-22 weeks the mother will start to feel the baby move for the first time. The baby has definite patterns of sleep and waking.

23-30 Weeks

The baby is very energetic. At 24 weeks the baby is viable, meaning it would have a reasonable chance of survival under intensive care if it were born at this stage and it measure 21cm and weighs 700g.

31-40 Weeks

The baby is growing plumper and has smooth skin, the lanugo disappears. At 36 weeks the foetus will engage' meaning drop it's head into the mother's pelvis ready for birth. The average weight at birth is 3-3.5 kg.

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