Researchers have found that fetuses at 34 weeks are like newborn babies in preferring face-like stimuli.

The team used a light source to project a pattern of three dots in the shape of eyes and a mouth through the uterine wall and measured the way the fetus responded using ultrasound.

The findings show that fetuses of 34 weeks gestation will turn their head to track the face-like pattern.

But there was no such movement when the team projected three inverted dots in the shape of a triangle, demonstrating that it was not the pattern itself which the fetus preferred.

Lead researcher and psychologist Professor Vincent Reid from Lancaster University said he was surprised by the findings, published in Current Biology.

“There was the possibility that the fetus would find any shape interesting due to the novelty of the stimulus. If this was the case, we would get no difference in how they responded to the upright and upside down versions of the stimuli.

“But it turned out that they responded in a way that was very similar to infants.”

This shows that experience of faces after birth are not necessary for newborn babies to show a clear preference for gazing at other people’s faces.

“This rules out the idea of filial imprinting, in the way that ducklings imprint on their mother, because we have shown that the preference for face like shapes is already present before birth.”

He said the discovery was made possible through advances in technology like high quality 4D ultrasound and the modelling of light penetration through human tissue.

“I would also say that if you are pregnant, don't go shining bright lights into the face of your fetus. We were very careful and made sure that the light was bright enough to enter the womb but not too bright as to be unpleasant or aversive for the fetus.”

Professor Reid said this discovery opens up a whole new field of research.

“We are improving the light source and plan to examine other aspects of fetal perception and cognition via visual systems. All sorts of aspects of human vision can now be explored.

“Newborns can discriminate numbers and quantities. Does the fetus in the third trimester also have these capacities?  Exploring the transition from fetus to infant is also a very exciting possibility.”