Womb with a view: Sensory development in utero

Sensory development utero ultrasound image.
From a very early gestational age, babies can sense the world around them.

A lot more than just physical development happens during the 40 weeks a baby spends growing in his or her mother’s womb. Not only are babies busy developing physical adaptations to function after birth, they are also eagerly sensing the world around them, starting from a very early gestational age.

Recent research has focused on the amazing sensory development that occurs long before a baby exits its mother’s womb. Much of this forms the basis of the infant’s early attachment to the mom and begins the long process of its learning about the postnatal world.

Touch

This is the very first sense to form, with development starting at around 8 weeks. The sense of touch initially begins with sensory receptor development in the face, mostly on the lips and nose. Over the next several months, touch receptors begin to develop on other parts of the body: the palms and soles by 12 weeks and the abdomen by 17 weeks.

However, brain scans on unborn infants suggest fetuses do not sense pain until after 30 weeks, when the somatosensory neural pathways finish developing. By the mid-third trimester, however, the baby is able to appreciate a full range of sensations, including heat, cold, pressure, and pain in every part of the body.

Sight

Although it is dark inside the womb, human skin does allow light to pass through and provide some illumination for the developing fetus. According to psychologist Vincent Reid from the University of Lancaster who has studied this issue, the uterus can be a surprisingly luminous place, “analogous to being in a room where the lights are switched off and the curtains are drawn.”

Based on this premise, Reid and his colleagues have studied the reaction of third-trimester fetuses to patterns of red dots shone into the womb. The babies’ reactions to different light patterns were monitored using high-definition ultrasound. Researchers found fetuses were about twice as likely to track the movement of dot patterns that resembled a human face, the same pattern and preference that has been demonstrated in babies after birth.

This suggests that our preference for human faces may be innate and not simply a result of experiences that occur after birth. Furthermore, it makes clear that the fetus actively responds to the external world long before he or she ever enters it.

Sound

It was first recognized in the 1980s that babies likely hear while in utero and are able to distinguish and identify voice patterns starting in the womb.

Starting in 1980, researchers demonstrated babies prefer their mother’s voice shortly after birth. By attaching a nonnutritive nipple to a tape recorder, the study showed newborns would suck more to hear their mother’s voice compared to a tape of stranger’s voice.

In a follow-up experiment, researchers asked pregnant women to read The Cat in the Hat to their unborn fetuses repetitively for the final seven weeks of their pregnancies for a total of 5 hours of exposure. After birth, researchers allowed infants to choose between two recordings using the same nipple-recorder device, one of their mothers reading The Cat in the Hat and the other of their mothers reading a different children’s book. The babies showed a consistent preference for the recording of The Cat in the Hat, presumably based on their prenatal exposure.

Since these initial studies, more research has been published suggesting fetuses are able to hear and even learn in the womb. 

Taste/Smell

Taste and smell are innately intertwined because our sense of taste is actually 90 percent smell. Some flavors, such as vanilla, carrot, garlic, anise and mint, have been shown to be transmitted into amniotic fluid, which babies live in and routinely drink several ounces of each day.

To determine this, researchers gave pregnant women both garlic and sugar capsules before taking a routine sample of their amniotic fluid. The samples were smelled by blindfolded panel members who could easily determine which samples came from women who ate garlic, providing indirect evidence that babies are experiencing these smells and tastes in utero.

To further test this theory, one group of pregnant women was instructed to drink carrot juice every day during pregnancy while another group was told to avoid it completely. Once the children began eating solid food, researchers fed them cereal made with either water or carrot juice. They found babies exposed to carrot in amniotic fluid ate more of the carrot flavored cereal!

Sensory development after birth

Evidence of early in-utero sensory development means we may be able to start influencing a baby's postnatal development based on the mother’s external sensory environment during pregnancy. We would do this by modifying factors such as maternal food intake or ambient music selection. However, the majority of an infant’s sensory development will still occur after birth. So while we can begin molding development early, the most impactful sensory stimulation will still occur once the baby exits the mother's womb!

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