Imma Perfetto
Cosmos science journalist
Humans can’t remember their time in the womb, but new research suggests it might not be so dark in there.
The first foetal eye movements can be seen on 2D ultrasound at 14 weeks of gestation, but it isn’t until 31 weeks that the pupils can constrict, dilate, and detect light.
So, what’s it like in the womb?
The new study modelled the how different coloured laser light penetrates through the layers of a pregnant person’s abdomen – skin, body fat, muscle, uterus, and amniotic fluid – to reach the foetus.
It determined that a red light applied directly to the skin would illuminate the womb to levels comparable to an overcast night, or even a full moon in clear conditions.
The findings will help in the design of future experiments to investigate how humans develop vision and perception before birth.
“There is a whole field here waiting to be explored, which is super important to our understanding of how we develop as humans,” says Professor Vincent Reid, a developmental cognitive neuroscientist at the University of Waikato, New Zealand, who led the research.
“Understanding how much light gets through to the womb means we can then think about implications. For example, what does that tell us about what the world of the foetus is like? Is it light enough for a foetus to see, and what would a foetus be able to see?”
Previous models of light transmission to the womb haven’t been specific to human tissue.
The new model considers how each layer of abdominal tissue will bounce, scatter, and absorb light in different ways, by incorporating the typical optical properties of each layer during the third trimester, as well as the range of fat tissue thickness seen across pregnant individuals.
Simulations showed that the intensity of light expected to reach the foetus increased with its wavelength, with red light able to penetrate the deepest.
As fat tissue absorbs light much more than the other layers of tissue, the amount of light that reaches the foetus also decreases as the thickness of the layer increases.
The research group will use these findings to design experiments to explore what the foetus sees in the womb and how it responds to light.
Reid says it provides direction on what sorts of shapes can be made with light to send to the foetus. It also informs the use of safe wavelengths and intensities of light to prevent any harm to foetal eye and maternal skin.
“Many researchers, including myself, have spent decades working with infants to understand how human perception and social development works,” he says.
“Our growing understanding of the uterine environment means we are learning that much of this experimental work with infants can be moved into understanding the third trimester.”
The paper is published in the journal Scientific Reports.
