by University of Waikato

Credit: Pixabay/CC0 Public Domain

New research from the University of Waikato nails down how much light travels from the outside world to babies in the womb, with far-reaching implications for understanding human development.

Published today in Scientific Reports, the study uses mathematical modeling to accurately simulate how much directly applied light will get through a pregnant person's skin, body fat, muscle and uterus to illuminate the womb environment.

Research lead Professor Vincent Reid says the study, which is part of his project examining how a fetus engages with the visual world, provides crucial insight into what it is actually like in the womb.

"The dominant thought has been that it is dark in the womb. This has only very recently been challenged, " he says.

"If you look at anatomy, biology or psychology books, they will say that it's dark in the womb, and that's a good thing, because eyes are sensitive when they first develop.

"Through the work we are doing, we've discovered that it's definitely not dark in there."

The Waikato research team—including Ph.D. student Zac Isaac and Associate Professor in the Department of Mathematics Dr. Jacob Heerikhuisen, as well as Professor Reid—determined that a red spectrum light applied directly to the skin will illuminate the womb to a level comparable to an overcast night or a full moon in clear conditions.

The paper's new, precise model uses the optical parameters of each layer of tissue to simulate how light will behave—for example, how much will bounce, scatter and be absorbed—as it passes through to the womb.

It confirms that light can be used for experimental research with a human fetus during the third trimester, a discovery that Professor Reid says lays the foundation for a brand-new field of science.

"There is a whole field here waiting to be explored which is super important to our understanding of how we develop as humans, " he says.

Previous models of transmission of light to the womb were not specific to human tissue, and instead were based on transmission of light through deceased chicken breast.

"Understanding how much light gets through to the womb means we can then think about implications, " Professor Reid says.

"For example, what does that tell us about what the world of the fetus is like? Is it light enough for a fetus to see, and what would a fetus be able to see?"

The work provides useful guidance to practitioners and researchers in the fields of fetal vision, ultrasound and developmental psychology.

Professor Reid says it provides direction on what sorts of shapes can be made with light to send to the fetus for future experiments.

"Many researchers, including myself, have spent decades working with infants to understand how human perception and social development works.

"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."

Professor Reid's research focuses on how humans develop perception and cognition before birth and in the first few years of life.

He pioneered the use of 2D and 4D ultrasound to experimentally study human development in utero—techniques which have spread to other fields, including epilepsy research and epigenetic robotics.

Other studies underway as part of Professor Reid's project investigate what the fetus sees in the womb and how the fetus responds to light.

With findings due to be published throughout the year, Professor Reid's teams are furthering our understanding of the development of human vision and perception.

More information: Zac Isaac et al, The effect of adipose tissue on transdermal monochromatic light presented to the human fetus using Monte Carlo simulations, Scientific Reports (2025). DOI: 10.1038/s41598-024-72686-4  Journal information: Scientific Reports