Researchers in the UK looked at the fetal facial movements of babies through 4D ultrasound scans during the last stages of pregnancy. They found the facial movements could actually be smiling or even crying rather than just little movements.
It's in the middle to later stages of pregnancy, specifically between 24 and 36 weeks that these facial movements get complex and more defined.
Babies at 24 weeks - the time the researchers began their observations - were able to move one muscle in their face at a time, either opening their mouth or stretching their lips.
By 35 weeks, the babies studied could stretch their lips and lower their eyebrows, turning little movements into complex expressions. Despite this, unborn babies cannot make any noises or sounds inside the womb.
These developments mean by the time a baby is born, he or she already has the movements needed to cry and laugh in the real world.
It's thought unborn babies practise the movements and expressions before they understand and feel the emotion, just as they practise breathing movements before they leave the womb and actually start to breathe.
Dr Nadja Reissland from the study said the team discovered much more than they ever thought they would with the research:
'We knew that the baby blinks before birth and that some research has identified scowling before birth.
'However in this study for the first time we have developed a method of coding and analysis which allows us to objectively trace the increasing complexity of movements over time which results in recognisable facial expressions.'
The research findings could help identify health problems in unborn babies as there is a link between behavioural problems and the development of a baby's brain.