Health

Human Fetuses Can See and React to Faces From Inside the Womb

A study found that fetuses at 34 weeks show a preference for face-like images projected through the uterine wall, confirming that they have visual experiences.

A healthy human fetus at 34 weeks of gestation can see shapes outside of the womb, according to new research that suggests that such unborn individuals pay special attention to people within view.

Prior studies have determined that other senses are active in human and animal fetuses, so the new findings, published in the journal Current Biology, add sight to the list.

“Taste, touch, smell, balance, and hearing are all active prior to birth,” lead author Vincent Reid of Lancaster University said. “Vision has been the difficult one to assess, until we developed our techniques for our current research.”

“The amount of light that enters the womb is certainly enough that the fetus can see and observe and interact with the world around them,” he added.

Innovations to ultrasound technology enabled the new study. Two-dimensional ultrasound, a traditional method used for years, provides a real-time, uniplanar image of the fetus. 3D scans show still pictures of the fetus in three spatial dimensions. 4D ultrasound, utilized for the study, adds time as the fourth dimension.

The researchers presented face-like patterns of light to 39 fetuses as they underwent the 4D ultrasound scans. In some patterns, the light stimuli —which put emphasis on the placement of two circles for “eyes” — were inverted. In others, they were upright as usual.

The scans revealed that the developing babies turned their head more often to look at face-like images that were upright versus those that were presented to them upside down. Infants upon birth are known to have a visual preference for human faces, so the determinations suggest that this affinity begins in the womb.

“When a baby looks at you, you tend to engage with them socially and treat them as if they are socially engaging with you,” Reid said, “so it is adaptive on the social level.”

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One of two possible mechanisms could explain why a fetus turns its head to a human-like face. The first is that the ability is innate. The other is that the skill involves visual perception and cognition, suggesting that some very rudimentary form of learning occurs in the womb. The researchers behind the study favor this latter explanation.

Reid believes that the facial bias “is triggered by exposure to patterned light in the womb and is due to prenatal vision experiences.”

“It is possible that the maternal rib cage could introduce variation in light penetrating the womb,” he explained, “and this may be enough visual information to create this bias.”

Research on infants further suggests that a baby’s upper visual field — typically the top half of whatever the baby is looking at — is developmentally more advanced and sensitive than the lower visual field. These differences could originate from fetal visual experiences in the womb.

The authors were quick to discourage pregnant mothers from shining bright lights into their bellies.

“A bright light would just brighten the whole womb and could be distressing for the fetus,” Reid noted. He and his team used low-level red light to minimize this problem, and because red wavelengths are known to penetrate through human tissue.

Reid also offered a constructive suggestion for expectant parents.

“This may sound unusual, but I would encourage expecting parents to read books to each other,” he said. “There is evidence that the fetus can detect the voice of their parents — not just their mother — but only if they have heard those voices frequently. This can help with bonding and could be beneficial, so I believe that reading books to each other is a good idea. This does not need to be books aimed at a baby. It could be anything.”

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The research team is now investigating whether or not fetuses of advanced gestation can discriminate between numbers and quantities.

“This is something that the newborn can do,” he said. “If the fetus can do this too, this tells us a lot about cognitive capacities.”

The researchers are also studying how fetuses see motion, since newborns exhibit a preference for people and things on the move. Reid suspects that if fetuses also show such an affinity, then “experiences that they have had engaging with their own body may have given rise to these preferences.”

Results from these studies could have multiple developmental and clinical applications in the future. For example, in terms of fetus health, clinicians might be able to do visual response assessments after medical procedures, such as fetal heart surgery, where oxygen deprivation might have occurred.

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