Babies learn to perform facial expressions of pain before they are born, according to scientists.
Researchers from Durham and Lancaster universities claim 4D scanning technology shows foetuses grimacing in the womb.
They suggest this ability is a "developmental process" that could help doctors to assess the health of an unborn child.
The study, which examined video footage of 4D scans of 15 healthy babies, builds on previous research that proposes the facial expressions of healthy foetuses develop and become more complex during pregnancy.
It found that when a mother is 24 weeks' pregnant, unborn babies are able to make simple expressions such as smiling, while by 36 weeks children are able to create "complex multi-dimensional expressions" such as pain.
"Our results show that healthy foetuses 'learn' to combine the necessary facial movements before they are born," said lead researcher Dr Nadja Reissland, of Durham University's Department of Psychology.
"This suggests that we can determine the normal development of facial movements and potentially identify abnormal development too. This could then provide a further medical indication of the health of the unborn baby."
It is not yet clear whether babies in the womb can actually feel pain, nor is it certain whether the facial expressions they pull relate to how they feel.
Researchers describe the process as "adaptive", claiming it helps the unborn baby to prepare for life after birth.
It seems to be related to brain maturation rather than being linked to feelings, they added.
Copyright Press Association 2013