Baby 'walking' in the womb

The new images also show foetuses apparently yawning and rubbing their eyes.

The scans, pioneered by Professor Stuart Campbell at London's Create Health Clinic, are much more detailed than conventional ultrasound.

Professor Campbell has previously released images of unborn babies appearing to smile.

He has compiled a book of the images called Watch Me Grow.

Conventional ultrasound, usually offered to mothers at 12 and 20 weeks, produces 2D images of the developing foetus.

These are very useful for helping doctors to measure and assess the growth of the foetus, but convey very little information about behaviour.

Complex behaviour

More pictures of developing foetuses

Professor Campbell has perfected a technique which not only produces detailed 3D images, but records foetal movement in real time.

He says his work has been able to show for the first time that the unborn baby engages in complex behaviour from an early stage of its development.

Professor Campbell told the BBC: "This is a new science for understanding and mapping out the behaviour of the baby.

"Maybe in the future it will help us understand and diagnose genetic disease, maybe even conditions like cerebral palsy which puzzles the medical profession as to why it occurs."

The images have shown:

• From 12 weeks, unborn babies can stretch, kick and leap around the womb - well before the mother can feel movement

• From 18 weeks, they can open their eyes although most doctors thought eyelids were fused until 26 weeks

• From 26 weeks, they appear to exhibit a whole range of typical baby behaviour and moods, including scratching, smiling, crying, hiccuping, and sucking.

  Until recently it was thought that smiling did not start until six weeks after birth.

An hour long session using the new technology, which is not yet available on the NHS, costs £275.