Fetal Psychology

Your baby can feel, dream and even listen to Mozartin the womb.

By Janet L. Hopson, published on September 01, 1998 - last reviewed on August 30, 2004

Along with such common movements, DiPietro has also noted some odder fetal activities, including "licking the uterine wall and literally walking around the womb by pushing off with its feet." Laterborns may have more room in the womb for such maneuvers than first babies. After the initial pregnancy, a woman's uterus is bigger and the umbilical cord longer, allowing more freedom of movement. "Second and subsequent children may develop more motor experience in utero and so may become more active infants," DiPietro speculates.

Fetuses react sharply to their mother's actions. "When we're watching the fetus on ultrasound and the mother starts to laugh, we can see the fetus, floating upside down in the womb, bounce up and down on its head, bum-bum-bum, like it's bouncing on a trampoline," says DiPietro. "When mothers watch this on the screen, they laugh harder, and the fetus goes up and down even faster. We've wondered whether this is why people grow up liking roller coasters."

FETAL TASTE

Why people grow up liking hot chilies or spicy curries may also have something to do with the fetal environment. By 13 to 15 weeks a fetus' taste buds already look like a mature adult's, and doctors know that the amniotic fluid that surrounds it can smell strongly of curry, cumin, garlic, onion and other essences from a mother's diet. Whether fetuses can taste these flavors isn't yet known, but scientists have found that a 33-week-old preemie will suck harder on a sweetened nipple than on a plain rubber one.

"During the last trimester, the fetus is swallowing up to a liter a day" of amniotic fluid, notes Julie Mennella, a biopsychologist at the Monell Chemical Senses Center in Philadelphia. She thinks the fluid may act as a "flavor bridge" to breast milk, which also carries food flavors from the mother's diet.

FETAL HEARING

Whether or not a fetus can taste, there's little question that it can hear. A very premature baby entering the world at 24 or 25 weeks responds to the sounds around it, observes Als, so its auditory apparatus must already have been functioning in the womb. Many pregnant women report a fetal jerk or sudden kick just after a door slams or a car backfires.

Even without such intrusions, the womb is not a silent place. Researchers who have inserted a hydrophone into the uterus of a pregnant woman have picked up a noise level "akin to the background noise in an apartment," according to DiPietro. Sounds include the whooshing of blood in the mother's vessels, the gurgling and rumbling of her stomach and intestines, as well as the tones of her voice filtered through tissues, bones, and fluid, and the voices of other people coming through the amniotic wall. Fifer has found that fetal heart rate slows when the mother is speaking, suggesting that the fetus not only hears and recognizes the sound, but is calmed by it.

FETAL VISION

Vision is the last sense to develop. A very premature infant can see light and shape; researchers presume that a fetus has the same ability. Just as the womb isn't completely quiet, it isn't utterly dark, either. Says Filer: "There may be just enough visual stimulation filtered through the mother's tissues that a fetus can respond when the mother is in bright light," such as when she is sunbathing.

Japanese scientists have even reported a distinct fetal reaction to flashes of light shined on the mother's belly. However, other researchers warn that exposing fetuses (or premature infants) to bright light before they are ready can be dangerous. In fact, Harvard's Als believes that retinal damage in premature infants, which has long been ascribed to high concentrations of oxygen, may actually be due to overexposure to light at the wrong time in development.

A six-month fetus, born about 14 weeks too early, has a brain that is neither prepared for nor expecting signals from the eyes to be transmitted into the brain's visual cortex, and from there into the executive-branch frontal lobes, where information is integrated. When the fetus is forced to see too much too soon, says Als, the accelerated stimulation may lead to aberrations of brain development.

FETAL LEARNING

Along with the ability to feel, see, and hear comes the capacity to learn and remember. These activities can be rudimentary, automatic, even biochemical. For example, a fetus, after an initial reaction of alarm, eventually stops responding to a repeated loud noise. The fetus displays the same kind of primitive learning, known as habituation, in response to its mother's voice, Fifer has found.

But the fetus has shown itself capable of far more. In the 1980s, psychology professor Anthony James DeCasper and colleagues at the University of North Carolina at Greensboro devised a feeding contraption that allows a baby to suck faster to hear one set of sounds through headphones and to suck slower to hear a different set. With this technique, DeCasper discovered that within hours of birth, a baby already prefers its mother's voice to a stranger's, suggesting it must have learned and remembered the voice, albeit not necessarily consciously, from its last months in the womb. More recently, he's found that a newborn prefers a story read to it repeatedly in the womb--in this case, The Cat in the Hat--over a new story introduced soon after birth.