Baby development

Fetal development: What your baby's up to in the womb

What life is like for your growing baby inside your womb.

By Camilla Cornell
Fetal development: What your baby's up to in the womb

When I was pregnant with my son, my two-year-old daughter, Carly, would plant her face against the mound of my belly and talk to the baby within. “Hi, baby,” she’d say. “Is it dark in there?”

If only Ben could have answered her question. By the time he was talking, his stay in my belly was a distant memory. But, for many years now, researchers have been trying to fill in the gaps in our knowledge of what babies feel, taste, hear and see in the womb. And their findings are beginning to have an impact on how we keep babies healthy, both inside and outside of Mom’s tummy.

Baby’s sense of touch A baby’s senses begin to develop in a predictable order, says Heidelise Als, an associate professor of psychology at Harvard Medical School and Children’s Hospital Boston. And the first to come on board is touch. By eight weeks of pregnancy, a fetus responds to touch around his lips and cheeks, and by 11 weeks, he has begun exploring his own body and his warm dark nest with his mouth, hands and feet. Ultrasound scans show babies “touching their buttocks, holding onto the umbilical cord, turning and walking up and down the amniotic sac wall on the inside,” says Als. “They are not passively quiet in the womb.”

In the nearly weightless, fluid-filled environment of the amniotic sac, Als believes the fetus uses touch to both soothe and teach himself. “Fetuses are laying down their own cortical networks in the brain,” she says. When babies are born prematurely, she points out, they continue to seek that interaction, but within a dramatically different environment: the neonatal intensive care unit (NICU). But the hard surfaces of the incubators neither yield to them nor cradle them. “You will see these little preemies trying to bring their hands together or bring their hands to their face, or lay them over their head and their ear,” says Als. “They search, literally, with their feet to try to find a boundary.”

The unborn child reacts strongly to his mother’s movements as well. Most moms notice that when they touch their belly, the baby kicks back or responds in some way, says Als. “If it’s a firm touch, they may move away and stick out their arm,” as if to ward you off.

Research shows that unborn infants respond to more than just physical touch—they respond to their mother’s emotional state as well. When mothers watch sad films, babies move less. But when a mother laughs, says Als, ultrasound images show that “the baby kind of trampoline bounces.” When she laughs harder, the baby bounces even more exuberantly. “It’s fascinating,” she says. “There’s such an interaction between mother and child on all levels.”

Message to Mom: The atmosphere in your womb is perfect for your baby to explore and learn, says Als. But since babies clearly react to their mothers’ moods, it’s good to try to keep stress levels to a minimum. If you have a high-stress job or are at a particularly hairy point in your life, you might want to take up meditation or some other activity that helps you regain your calm.

Baby’s taste recognition Whether your child grows up to be a cookie monster or adores curry may have something to do with what you eat during your pregnancy. By the second trimester, your fetus’s taste buds look just like those of a mature adult, and the amniotic fluid surrounding her can carry the odour of curry, garlic, anise or vanilla, for example.


“Research has shown us that not only is the machinery [to] there,” says professor Julie Mennella, a biopsychologist at the Monell Chemical Senses Center in Philadelphia, “but infants will respond differently to a flavour they experienced in amniotic fluid as well as in the mother’s milk.” For example, when Mennella randomly assigned a group of mothers to either drink carrot juice regularly during pregnancy or lactation, or to avoid carrots, she found that “the babies who had experienced the flavour of carrots either in amniotic fluid or in mother’s milk were more accepting of that food at weaning.” Other studies have found that babies make less negative faces in response to the smell of foods like garlic or anise if their mothers ate the food while pregnant.

Mennella’s theory is that fetuses form memories of flavours from being exposed to them in the womb. “During the last trimester, a fetus swallows up to a litre of amniotic fluid a day,” she points out. The fluid flows over the olfactory receptors in their noses and the taste buds in their mouths, and may act as a “flavour bridge” to breastmilk, and then to table food.

That doesn’t mean your infant’s sense of taste is fully developed before birth. Although doctors have noted that a 35-week-old preemie will suck harder on a sweetened nipple than on a plain rubber one, babies are born unable to detect the taste of salt. That particular taste experience doesn’t become known to them until about four months after they are born. It’s the brain that is perceiving this, says Mennella. “The sense of taste continues to develop throughout childhood and adolescence.”

Message to Mom: You’re definitely eating for two and your baby is learning about your food choices, so try to eat a healthy diet. But don’t stress unduly if you can’t bring yourself to choke down some spinach. “Our biology is not necessarily our destiny,” Mennella explains. “A child can learn to like green vegetables.”

I hear you! Your fetus’s ears begin to function while he’s still firmly ensconced in your womb. Ears are well developed at about 20 weeks’ gestation, according to Barbara Kisilevsky, a professor in the School of Nursing at Queen’s University in Kingston, Ont.


By 26 or 27 weeks, fetuses respond to sound and vibration applied to mom’s belly. “They will move or their heart rate will change,” says Kisilevsky. By 30 to 32 weeks, they generally hear “airborne” noise, such as voices or music — you might notice they kick or startle to a door slamming or car backfiring.

In addition, they become accustomed to the soundscape of the womb — the steady thump of mom’s heartbeat, the whooshing of blood through her blood vessels, the rumbling of her stomach and, most importantly, the tones of her voice filtered through tissues, bones and fluid. Research on newborn infants shows that they will turn their head when they hear their mother’s voice more often than when they hear the voice of a female stranger, says Kisilevsky.

What’s more, infants seem to remember what they hear in the womb, preferring familiar pieces of music or books. In one famous experiment, a group of mothers read the Dr. Seuss story The Cat in the Hat out loud regularly during their pregnancy. At birth, their babies were hooked up to recordings which they could “select” by sucking on a non-nutritive nipple. After a few trials, babies learned to suck at whatever speed was necessary to obtain their mother’s voice reading the familiar story. “They wouldn’t understand the meaning of the words,” says Als. “But they like the mood and the familiar rhythms of the music or the words.”

There’s even evidence that the roots of bilingualism go as far back as the womb. A study published last year by University of British Columbia psychology professor Janet Werker and her colleagues found that the rhythm of a mother’s language helps prepare her infant for language development once the baby is born. Newborns sucked more on a pacifier hooked up to a computer when they heard their mother’s native tongue, the researchers noted, indicating that they were paying attention. If their mother spoke two languages, the newborns showed equal interest in both, but if the mother spoke only one, they ignored the unfamiliar language.

Message to Mom: So does that mean you should strap an iPod to your belly and blast some Mozart, or perhaps L’Etranger in French? “I don’t think we know enough to say whether that’s going to make a difference,” says Kisilevsky. “Music and voice are already often a part of our environment. To my knowledge, there’s nothing that shows it makes a difference whether you listen to Mozart or heavy metal.”


A warmer welcome for preemies The womb, says Harvard professor Heidelise Als, is such an ideal environment for the unborn child that leaving it too soon can have a lifelong impact, particularly on the youngest preemies, who face a higher risk of physical, psychological and intellectual problems.

Als has spent much of her life trying to see, hear and feel the world through the eyes, ears and fragile skin of premature babies. As she sees it, these teensy newcomers are basically launched out of a warm, dark bath into a chaotic environment of glaring fluorescent lights, hard surfaces and cacophonous sounds, and their brains are not yet wired to deal with it. So Als advocates trying to recreate, as much as possible, the nurturing womb environment for preterm babies born in hospitals.

For starters, she has managed to persuade the hospitals she works with around the world to keep the lights low in NICUs, covering incubators with a blanket to block out the light, and using task lighting for medical procedures. In addition, she advocates surrounding preemies with a nest of blankets, keeping noise levels to a minimum, and simply keeping preemies’ needs foremost when caring for them.

In the long run, Als would like to see NICUs kept very warm (at least 25 to 27°C) and incubators go the way of the dodo bird. Premature babies (even those hooked up to oxygen) should be allowed to cuddle skin to skin with their parents, she believes, touching or licking the mother’s skin with their hands, mouth and feet. Although it’s impossible to recreate conditions in the womb exactly, Als contends, “we can do much better.”

A womb with a view? To finally answer Carly’s question: Yes, it is dark in there. An unborn infant, says Als, is basically peering through a fog of amniotic fluid into a dark cave. It’s possible that a bright light might filter through to the womb but, to the infant, it probably means the difference between dim and dimmer.


Although your fetus is not seeing much, she is developing and perfecting the “equipment” she needs to see. By 23 to 25 weeks, a baby’s eyeballs are formed and she begins to blink. Another five weeks or so and her pupils have begun to contract in response to a bright light. The infant begins to exercise those visual muscles in preparation for a time when she will see, says Als. “They have a lot of eye movements and those movements have been found to be very important for visual brain development.”

In fact, Als believes that when fetuses are born too soon, their brains are not prepared for signals from their eyes to be transmitted into the frontal lobes of the brain. She fears that when a premature baby is forced to see (as well as touch, smell, taste and hear) too much too soon, the overstimulation can lead to aberrations in brain development, perhaps partially accounting for the fact that children born prematurely face higher rates of ADHD, learning disabilities and other disorders.

Message to Mom: Your full-term baby will take care of his visual needs all on his own, but Als is doing her best to make NICUs a little more like the womb.

This article was originally published on Mar 14, 2011

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