Life in the Womb
The test is positive! Until now, you have been listening politely as your “nouveau-parent” friends regaled you with their triumphs and tribulations with their enchanting offspring. But now you suddenly begin to picture yourselves in their position. What will your own baby be like? Will it be a rough-and-tumble boy who will play the trumpet, join you in a game of chess, accompany you on long hikes in the woods? Will it be a girl with organizational talent who takes over the family business? You are sure of one thing: you are determined to do everything in your power to give your new family member the best possible start in life.
During the very first weeks after conception, before you even know for sure that your baby is more than just a dream, she has already accomplished some big steps on her way to becoming a real individual. At around 20 days, the baby’s heart muscles start beating. A few days later, the first signs of the baby’s future arms and legs appear. The baby’s brain gets off to an even earlier start, and it needs to. It has a big job ahead, namely, to prepare the baby for life outside the uterus in the short span of only nine months.
The Brain Takes Shape as It Goes to Work
By the embryo’s second to third week of existence, when it is only about one-eighth of an inch long, the brain begins to form. (Biologists and medical personnel use the term embryo to describe the new human being up to the end of the third month and fetus for the remaining time before birth. Parents, understandably, prefer to use the word baby.) As in an artist’s preparatory sketch, the faint outlines of the future structures of the brain emerge before the details are filled in. The basic design and the timing of construction follow the instructions contained in the baby’s genes. While some of the structures will take up their functions before birth, others will gradually join up later.
At the end of the first month a crevice appears, separating the future left and right hemispheres. These visible halves of a single sphere are the source of fascinating and often fanciful “left brain–right brain” theories about our personalities and dispositions. While the two halves will gradually become more specialized for performing particular functions, they will always continue to act together and complement each other.
Until around the seventh week, the baby’s brain and body are built up according to a sexually unspecific pattern. However, if the baby’s genes contain instructions for a male, a special factor will now trigger the formation of male sex organs. The sex organs begin to produce the hormone testosterone, which will exert its influence on the developing brain structures, making the male brain different from the female brain and thereby affecting the timing of brain development.
For all the rapid construction taking place in the brain, a tremendous number of nerve cells, the basic building blocks of the nervous system, have to be formed. Between the baby’s second and seventh month in the uterus, more than 100 billion nerve cells, called neurons, are formed, roughly half the number of stars in the Milky Way. This means that at times more than 250,000 neurons are formed per minute. We used to think that all the nerve cells we would ever have were generated before birth. However, recent research suggests that some limited nerve cell formation takes place even in adult life.
From the moment they are formed, the immature nerve cells migrate to their genetically predetermined locations in the baby’s brain. To give you an idea of the magnitude of the distances involved, the neuroscientist Pasko Rakic has said that if nerve cells were the size of people, it would be as if the whole population of the United States were to migrate from one coast to the other. The first cells to form stake their claims on the closest sites, leaving the latecomers to blaze a trail through them to find their final destinations. It is a miracle that so few neurons go astray on their long march through the crowds. However, when many cells do get lost—for example, as a result of infections—it may be a factor in developmental disorders such as cerebral palsy, epilepsy, mental retardation, and autism.
Along the way, the neurons start to take on the specific form that will enable their specialized functions later. They grow branches called dendrites, which receive signals, and an extension, or axon, which transmits the signals further. Upon arrival at their destinations, like students at a new school, the neurons begin to actively seek contact with other neurons and form connections, called synapses. The famous Spanish neuroscientist Ramon y Cajal romantically referred to synapses as “protoplasmic kisses.” At the synapse, the axon of one neuron meets the dendrite of the next neuron without quite touching it. Chemical messenger substances called neurotransmitters carry the cell’s message across the gap.
Around the seventh week of the baby’s prenatal life, neurotransmitters are already detectable. These may play an important role during the early phases of brain development by stimulating the growth of the brain structures and only later function as actual “messengers.” A few weeks later, synapse formation begins in earnest. However, most synapses will be formed after birth.
Forming synapses is a matter of life and death for the cell. Neurons that fail to make a connection wither and disappear in a process known as apoptosis. While apoptosis may sound tragic for the single neuron, it is essential for brain development and allows more resources for important connections.
Imagine yourself lying quietly in bed, thinking over the fact that the first half of your pregnancy is about over. Suddenly you feel a vague, bumping sensation in your abdomen, like something small pressing against the wall of your uterus. Yes, it moved. There it is again! You call the baby’s father, and if he’s quick enough he can reach over and feel the movement with his hand.
Until recently we could only imagine what babies are doing within the warm, dark confines of the uterus. Now modern ultrasound techniques provide new insights into the baby’s activities, even if they don’t give us clear pictures like closed-circuit television cameras. Ultrasound is used in routine examinations and is not harmful for the fetus.
We now know that a baby begins to move long before her mother can feel her motions. As early as about the end of the second month after fertilization the muscles of the tiny embryo begin to twitch. The muscles react asymmetrically. Those on the embryo’s right side are more active than those on the left.
At around three months the baby begins to perform motions that look more like “practice” for postnatal life. Instead of moving and twisting her whole body at once, the fetus begins to move her limbs singly—one arm or one leg at a time, for example. Again, most fetuses move their right arm more than their left.
Single-limb movements are possible because nerves from the baby’s spinal cord have now grown long enough to reach and make contact with the muscles. The nerves in the baby’s spinal cord are now able to send signals to the muscles, causing them to relax or contract.
The baby is not only exercising her arms and legs but is also practicing many movements that are essential for eating, drinking, and breathing. She begins to open and close her jaw, move her tongue, and make sucking and swallowing movements. Movements can be detected that resemble a prenatal yawn and hiccup. A few weeks later, a fetus can even suck on her thumb, and we’re not surprised to hear that it is most often the right thumb. These movements are a sign that the baby’s brainstem is now an active member of the motor team.
With respect to mouth movements, Peter Hepper and his colleagues at Queen’s University in Belfast observed interesting gender differences in fetuses at the tender age of four to five months. Using ultrasound techniques, they saw that at four months male and female fetuses made about the same number of mouth movements. But a few weeks later the females were way ahead of the males. No long-term conclusions about future verbal abilities or conversational habits should be made on the basis of this finding. However, it is an indication that females are ahead of males in brain development by this time.
Around the time when a pregnant woman first becomes aware of her baby’s activity, at about five months, the fetus’s movements become more coordinated and smoother than before. This is because new structures now join up with the motor team, putting movements of the muscles under increasingly higher levels of control. At around four months after fertilization, the baby’s cortex is just beginning to exert its influence. This is the time when neurons from the baby’s motor cortex, the part of the cortex that controls muscle movements, make connections with the neurons in the spinal cord.
Feeling My Way Around: The Sense of Touch
As a baby grows in the uterus, her senses are already busily receiving information from both outside and inside her body. The stimulation inside the uterus is just what the developing systems need. A baby’s sense of touch develops early and gets a lot of practice before birth. As a fetus moves, she bumps against the uterine wall, and sometimes her tiny hands brush up against her face. Between two and five months after fertilization, touch receptors develop in the baby’s skin. The first to appear are those around the mouth, and they will be more numerous in this region, which is why babies explore so many things with their mouths. Although the touch receptors register a sensation automatically, they are not yet linked to higher centers.
Between five-and-a-half and seven months after fertilization, contacts are established between the touch receptors and cells in the baby’s somatosensory cortex, the part of the baby’s cortex that is specialized for touch sensations. Somato is derived from soma, the Latin word for “body.” After an initial processing in the so-called primary area of the somatosensory cortex, the information from the touch receptors is passed to higher cortical areas, which put the information together. Now the baby becomes able to register the sensation of touch.
Together with maturational changes in the brain, the fetus’s experience with touch stimulates the growth and specialization of the neurons in her somatosensory cortex, making them ever more efficient at processing touch sensations. Around this time, it is likely that a fetus could also feel pain.
Can You Hear Me in There?
The evangelist Luke, who was also a physician, showed a good knowledge of fetal behavior when he wrote: “And when Elizabeth heard the greeting of Mary, the babe leapt in her womb” (Luke 1:41). This was around the sixth month of Elizabeth’s pregnancy. Contrary to the opinion of Luke, medical authorities still claimed until the early part of the twentieth century that unborn infants weren’t able to hear. In 1925, Dr. Albrecht Peiper, a doctor in the Berlin University Children’s Hospital, made an interesting observation. He played a few notes on a toy trumpet to some newborn babies—the youngest was just 25 minutes old—and noticed that their body movements changed.
Intrigued, Peiper decided to see if babies could hear while they were still in the uterus. Women in the last weeks of pregnancy were asked to lie quietly so they could feel the movements of their babies. Peiper wanted to exclude the possibility that the mother’s startle or change in breathing had an effect on the infant’s behavior, so he gave a warning count before he blew a loud blast on a car horn. Some of the babies reacted with a thump against the wall of the uterus; others wriggled around for a while. After he repeated the sound several times, the babies reacted less. Peiper made a note that the babies behaved consistently on later repetitions of the experiment, but he didn’t mention that this might reflect the baby’s individual style.
Ultrasound techniques and heart-rate measurements confirm that fetuses begin to respond to sound at around five months. They startle at a sudden noise, blink, and stop moving around, and their heart rate decreases momentarily. Around this time, the baby’s cochlea, or inner ear, begins to function. This is the time when nerve fibers grow out from the thalamus to make their connections in the baby’s auditory cortex.
How much does a fetus actually hear? She is surrounded by the sound of the swishing noises—doctors call them borborygmi (bor-bor-IG-me, rhymes with pygmy)—of her mother’s intestines. The general sound level in the uterus can reach about 70 decibels (dB), similar to the level we perceive when we run a vacuum cleaner. Her mother’s heartbeat can be felt as vibrations. Her mother’s voice rises about 24 dB above the background sounds and is also transported directly as vibrations, so by her last month in the uterus, the baby can definitely hear it. Studies have shown that a whole month before birth, fetuses are able to distinguish among music, heartbeats, and speech sounds.
During “our” sixth month of pregnancy, we were walking in San Francisco at Chinese New Year time. All around us, we heard the nervous popping of firecrackers on the sidewalk. Elinore felt that each volley of firecrackers was met with a vigorous drumming from inside her uterus. Our son didn’t grow up to play a percussion instrument, but we often joked about his fascination with fireworks.
The View from Inside
The view really isn’t much, perhaps at most a faint orange glow during the last weeks before birth. But even in the dark, your baby’s visual system is under intense construction to prepare her for her life in the world of light. Already at around one month after fertilization, when the first traces of her brain as a whole come into view, tiny bulges that will become the baby’s eyes appear.
Carla J. Shatz, now chair of the Department of Neurobiology at Harvard Medical School, showed in animal experiments that the basic wiring of the visual system begins to take place before any stimulation from the outside world reaches the baby’s eyes. In the absence of light, special nerve cells in the retina of the eye called ganglion cells begin, probably under genetic influences, to fire off short bursts of electrical impulses. The impulses are transmitted from the retina along the optic nerve to the brain. The spontaneous electrical activity of these retina cells seems to be crucial for setting up the correct wiring. If it does not take place, vision will not develop normally.
The impressive groundwork takes place all by itself without any extra outside stimulation. However, adverse environmental conditions may prevent necessary developmental steps from taking place. The spontaneous firing of the nerve cells in the visual system is vulnerable to disruptions. Drugs that interfere with the transmission of electrical activity across the synapse (e.g., nicotine, benzodiazepines, or narcotics) could disturb the pattern of the fine connections and lead to later visual deficits.
By the time your baby is born, her visual system is basically set up. But it will need the stimulation of the outside world to complete the job—and there is plenty out there waiting.
What’s for Dinner?
You might have heard that newborn babies recognize their own mother’s milk and sometimes even turn up their noses at it if she has tried some unusually spicy food. This means that the systems for taste and smell are well developed by the time the baby is born.
Taste and smell are similar in that they are “chemical senses.” That is, they involve direct contact with molecules of the chemicals that make up the substance the fetus perceives through her mouth or nose. Special receptor cells convert the chemical into an electrical signal. After passing through a series of relay stations, the signal reaches the baby’s cortex, where it can be registered.
Sometime between two and three months after fertilization, taste buds appear on the edge of the baby’s tongue, on the roof of the mouth, and in the upper throat area. Some taste buds and their connections to the brain are already functional by the third trimester of pregnancy. But they become more numerous and continue to develop throughout the rest of pregnancy and even for a few months after birth. Evidence that babies’ taste systems develop early is the fact that babies born prematurely at 24 weeks already show a basic sense of taste.
At around four to six months after fertilization, the plugs blocking the baby’s nostrils disappear, making it possible for chemical substances in the amniotic fluid to come in contact with the receptor cells in the baby’s nose. During the third trimester the olfactory receptors for the sense of smell are developed. Although your baby can’t yet share your dining pleasure, some signals—strong flavors such as garlic—may be getting through.
Learning in the Womb?
We know that while babies are growing in the uterus they are stretching and turning and that their senses are diligently processing incoming information. But are they able to form memories? And if so, do these memories affect the baby’s behavior; that is, do they represent an early form of learning? Dr. Albrecht Peiper, of the car horn, did not agree with the many scientists of his time who believed that the capability to form memories
begins only after birth. He had observed that fetuses reacted intensely when they first heard the car horn. But after they heard the horn several times, they reacted less and less and eventually stopped moving around. He proposed that the sound left a trace that inhibited further reactions to the sound and wondered if this Merkfähigkeit, or ability to remember a stimulation, was an early form of memory.
Later studies have confirmed and extended Peiper’s observations. The “memory trace” that Peiper referred to is now called habituation, which is considered one of the simplest, yet essential, learning processes. Habituation, which will play an important role all through life, is the ability to react less strongly to a repeated stimulus. After their initial startle, the babies got used to the sound of the car horn. Ultrasound techniques have demonstrated that fetuses as young as 23 weeks after fertilization are able to habituate. Habituation appears first in females, a further indication that the female nervous system is on an earlier schedule than the male.
To find out how long fetuses can keep a memory, Peter Hepper played a particular tune to mothers during the ninth month of pregnancy. He played it loudly and often enough that the fetuses had a good chance to become familiar with it. One week after birth, the babies behaved differently when they heard the familiar tune from when they heard one that was new to them. But two weeks later, they didn’t distinguish between the familiar and unfamiliar tunes anymore. This shows that the fetuses could form a memory, but it was only of short duration.
We know that in the mature nervous system a structure called the hippocampus is important for memory formation. It is, therefore, of interest that this structure undergoes intense development at around five to six months after fertilization. However, to store a memory for a longer time—over months, years—the brain has to transfer it to the baby’s cerebral cortex. This transfer does not appear to be taking place at two weeks after birth.
The current knowledge about how memories are formed and learning takes place suggests that it is unlikely that unborn babies form lasting memories. However, basic processes involved in memory and learning are under way during the baby’s time in the uterus, forming the foundation for a running start at birth.
Even before people had any idea of what babies are doing in the uterus, they considered trying to influence the child’s development. Talmudic writings from the second to sixth century contain references to prenatal stimulation programs. It would be interesting to know their “curriculum.”
When Frank Lloyd Wright’s mother was pregnant, she hung up pictures of English cathedrals and spent a lot of time looking at them in the hope that it would have an effect on her child. As we know, Frank did go on to become an architect and, in fact, announced early in his career that he intended to become the greatest architect who ever lived. However, the reasons for his success can be found in the combination of Frank’s own talents, his personality, and his mother’s encouragement after he was born. If a mother’s thoughts alone were enough, how different parenting would be!
In recent years, scientific reports on the ability of the fetus to learn have sometimes led to the assumption that early stimulation might speed up brain development and lead to greater achievement in postnatal life. In his 1992 review of prenatal influences, Peter Hepper notes that there have been some anecdotal reports that prenatal stimulation has an effect, but scientific evidence for this idea is lacking. Any benefits are likely to be due to the increased interest of the mother in her pregnancy and the resulting positive effects on her lifestyle both before and after the birth of her child. The natural environment of the uterus provides all the stimulation the baby’s brain requires.
If additional stimulation could speed up development, premature babies, exposed earlier than normal to the outside world, would be ahead of babies who spent the full term in the womb. But our own studies show that, in spite of their earlier exposure to outside stimulation, babies born after only 32 weeks do not have a head start over full-term babies. Dr. Petra Hüppi, of Boston and Geneva, Switzerland, used behavioral scales and magnetic resonance imaging (MRI) techniques to monitor and compare the development of premature and term-born infants. She compared the preterm babies at their expected due date at 40 weeks to term babies born at 40 weeks. In spite of their eight-week head start, the premature babies’ development was delayed. The eight weeks that the term babies had spent in the uterus were apparently beneficial.
Although the development of brain structures is not speeded up by extra stimulation before birth, negative influences can impair a baby’s brain development. Alcohol, nicotine, drugs, and malnutrition are known risk factors, as are X rays and some
Does a Mother’s Stress Affect the Baby?
If you are racing around from one appointment to another, struggling to balance school schedules, deadlines, and menu plans, to say nothing of trying to find a quiet moment to collect your thoughts, you may worry about what effect your daily hassle could have on your baby’s brain. As early as 480 B.C., Empedocles suggested that the development of the embryo could be guided and interfered with by the mental state of the mother. And 1000 years ago in China, “prenatal clinics” were established to keep mothers tranquil, which was thought necessary to maintain the psychological health of the fetus.
In the early 1970s, scientists began to approach this question in a systematic way. Researchers in Canada studied the relationship between a mother’s stressful situations during pregnancy and the baby’s postnatal development. The investigators found that mothers who suffered constant high, personal tensions during pregnancy, mainly marital discord, had children who had an increased risk for eczema and tended to reach motor milestones later than infants of mothers whose pregnancies had been more relaxed. The babies also tended to be more fretful and restless and to have difficulty quieting down. The authors suggested that changes in the endocrine system of the mother resulting from stress could affect her unborn child.
Everyday life is full of short-term events that, depending on your personality, may be perceived as “stressful”: you are frightened by a sonic boom, your two-year-old races out into the street, your boss criticizes the report you worked on all weekend. Your nervous system reacts to these sudden events by causing a surge of adrenaline into your bloodstream. This surge may lead to a restriction of blood flow to the uterus, similar to the effect of a mother’s smoking. The fetus detects the change and “sympathizes” with your upset condition: her nervous system also produces more adrenaline, causing a temporary change in heart rate and body movements. Another way in which maternal mood can affect the fetus is through the hormone cortisol, which mobilizes the body in times of stress. If the mother is highly anxious, her body produces more cortisol. Some of this passes directly to the fetus, and some acts over the placenta to stimulate the baby’s own endocrine system. Sporadic bouts of stress or low-level “worry” have no long-term effect on the baby’s development.
Prolonged and severe stress during pregnancy, however, may have consequences. Reduced blood flow to the placenta may restrict the baby’s growth and lead to the condition known as “small-for-date.” Recent studies have linked high levels of mothers’ reported anxiety, particularly during the latter part of pregnancy, to a cluster of behavioral problems that appear in early childhood. These include hyperactivity/inattention, particularly in boys, and emotional problems in both boys and girls.
It is important to realize, however, that the infant’s brain is constantly shaped by her experiences after birth. This gives parents the opportunity to counteract the effects of the prenatal stress by adjusting their childcare techniques to meet the needs of the child. This could mean, for example, providing a calm, “predictable” environment and avoiding excess stimulation.
Signs of Individuality
My neonatologist friends have frequently told me that babies react very individually to routine ultrasound procedures. Some get excited and kick back at the ultrasound head, while others remain quiet. These differences might have something to do with a baby’s temperament. Knowing more about this pattern would help us to learn about a baby’s early characteristics that are not influenced by her experiences after birth.
A 1999 study confirmed what mothers have experienced all along: that babies show individual patterns of activity while still in the uterus. At the middle of the eighth month, investigators measured the rate of the fetus’s general spontaneous movements on three different occasions using ultrasound techniques. Each child showed a clearly individual pattern of body movements. The researchers then compared these data to the baby’s activity during the second and fourth week after birth. The babies who moved more often or kicked around with greater energy before birth were the ones who were also more active during their first months outside the uterus.
Ready to Go
The 40 weeks of pregnancy seem long enough to you, but it is an amazingly short time for all the intense building activity that has to go on in your baby’s nervous system. By birth, the production and migration of the nerve cells are practically over. Brain structures are in place, and the major connections are functioning. While the brainstem, the structure responsible for vital functions, is practically fully developed, other structures undergo major construction after birth. The main bridge, or corpus callosum, is beginning to link the brain’s two hemispheres. Neurotransmitters are being synthesized. Electrical activity is going on.
The preferential treatment that a baby’s brain enjoys at this early stage is illustrated by the fact that her total birth weight is only 5 percent of what she will weigh as an adult, while the weight of her brain is already 30 percent of adult brain weight. Additional evidence for the brain’s importance at this time is the amount of energy it needs. While the adult brain uses only 20 percent of the body’s total energy supply, the newborn’s brain consumes almost all of it.
Networks involved in vital functions, such as breathing and circulation, are ready to go into action immediately at birth. Your baby’s sensory systems are ready to take in the wealth of stimulation awaiting her in the outside world. She has been moving her trunk and limbs by contracting and relaxing her muscles in practice for her new life outside the womb. Her sense of touch is ready to respond to your caress.
The ability to transport fragile memories formed in the uterus over the bridge into postnatal life will help your baby feel at home in her new surroundings. The melody of your voice and the scent of your body help the baby find nourishment and a haven of comfort and security.
Will extra stimulation help my baby’s brain development?
We now know that life in the womb offers a great deal more stimulation than we might think at first. This stimulation is indeed important for the development of the embryo and fetus. But there is no proof that more is better. If you find listening to Mozart enjoyable and relaxing, if reading Dr. Seuss aloud is practice for reading to your child later, or if prenatal programs make you more interested in your child’s development, this kind of “indirect stimulation” is most likely beneficial.
Should I eat for two?
Even if you don’t need to eat twice as much during pregnancy just because you are eating for two, you do need to consider the additional requirements for the growing baby. Consult your doctor about a supplement of folic acid. Be sure to eat a balanced diet with all the foods that are good for you, too: fresh vegetables, milk or soy products, hearty whole grains, luscious fruits.
Which substances have been proven harmful to a baby’s brain
Some substances are known to have negative effects on a baby’s brain development. It’s certainly best to avoid alcohol, nicotine, and illegal drugs entirely. In high doses, X rays and radiation can lead to stunted brain growth. Becoming overheated, especially during the first trimester, is to be avoided. Treat fever with a drug approved by your doctor, and stay away from hot tubs and saunas. Immunization against chicken pox and rubella should be undertaken before you become pregnant. Avoid organic solvents such as toluene or benzene, or use them only in well-ventilated rooms.
Are modern electronic devices dangerous?
To balance the list of dangers, it’s a relief to know that many modern devices such as video displays and microwave ovens have not been proven to be harmful. Neither ultrasound nor MRI procedures have been shown to be a risk for the infant. However, MRI should be avoided in first trimester until more is known.
When is caution necessary?
A pregnant woman should consult her doctor or other health care provider before taking any drugs or medication of any kind, including herbal remedies. Although they may look “natural,” many of these contain unspecified amounts of substances that could be harmful. If you can’t do without that morning cup of coffee, limit your coffee intake to no more than two cups a day.
Since influenza presents a possible risk to the fetus, take care during the flu season. A simple but effective means of reducing the chance of contact with the flu virus is to wash your hands frequently and avoid touching your mouth or nose.
In 1997 the American Academy of Pediatrics warned that excessive noise could have harmful effects on the development of the unborn child. Studies have shown a correlation between high noise levels and high-frequency hearing loss in newborns, increased risk of preterm delivery, and decreased birth weight. However, more studies are necessary to determine whether the noise itself was the cause or whether the problem is also related to unfavorable socioeconomic conditions.
What is meant by “excessive noise”? A general recommendation is not to be exposed to much above 80 dB for any length of time. To give you an idea, this level is about the noise of heavy traffic. A power mower is about 100 dB, and the noise really becomes “excessive” with a boom box in a closed car—about
120 dB! Jet planes overhead can bring the noise level up to 140 dB. In addition to the effect of a general high noise level on the baby’s hearing system, unpredictable loud noises, such as the roar of planes taking off or landing at a nearby airport, can be stressful for the baby’s mother.