Get ready for the fourth trimester
By Susan Brink
Pity the poor elephant cow, pregnant for nearly two years. There is hardly a human mother alive who, after nine months of pregnancy, who wouldn’t say she was ready to get on with labor, delivery and childrearing. But what if we thought of human gestation as taking a full calendar year, rather than the 40 weeks we’ve always counted off?
Newborn infants arrive in this world somewhat half-baked, or in the more measured words of evolutionary anthropologist Wanda Trevathan of the University of New Mexico, “a little unfinished, if you will.”
Human infants at birth are the least neurologically developed primates on earth, their brains a mere 25% developed, compared to about 50% among monkeys and chimps. Parents might well think of human infants as final-phase fetuses who will spend a fourth trimester outside the uterus crossing the divide between womb and world.
Multiple branches of science– evolutionary anthropology, neurology, biology, and developmental psychology—show that the first three months of life are a crucial bridge to life in the world we all know. Newborns are born with billions of neurons, or brain cells, the raw material for learning. But the infant brain still must lay down dendrites and develop synapses, the communication networks that will result in vision, in gathering the basic tools for language, in circadian rhythms to distinguish night from day, and in the ability to receive and give love.
This biological activity mingles with the real world of mothers, fathers, sounds, sights, tastes and smells. The environment that welcomes them works with their natural capabilities to fashion each newborn into the unique and irreplaceable baby parents have been waiting for.
Here’s what the world might sound like to an infant: Grown-ups chattering, siblings nattering, pots and pans clattering. A brand new baby hears it all, but cannot sort through the din of this chaotic world. Still, hearing is the most developed sense at birth. An infant recognizes and responds to a mother’s voice from day one. He or she has heard it, after all, for nine months through the walls of the uterus. But as for the countless other sounds around them, one is no more or less important than the next.
But don’t think that these undifferentiated noises are useless. With an innate skill that would be the envy of a statistics student, newborns are keeping track of probabilities, setting up neural connections in response to the patterns of the words they hear. They are learning where one word ends and another begins long before they utter their first da-da.
Babies around the world are born with the ability to hear the sound distinctions of every language spoken on earth, according to research by Patricia Kuhl, neuroscientist at the University of Washington and a leading expert on early speech development. Before they’re a year old, that ability is lost, pruned away by a brain eager to cultivate what will be needed, and get rid of what won’t. Japanese infants, for example, can distinguish the syllables “la” and “ra.” But since those sounds won’t be needed in their homeland, their brains, in a necessary “use-it-or-lose-it” model, gets rid of the unused neurons. That’s why so many Japanese people, when learning English, have trouble with words like “rice” and “lice.” Their infant brains never made the distinction because the Japanese language has no such requirement.
It’s more difficult to imagine what the world might look like to a newborn. Vision is the least developed sense at birth. But we know that even brand new babies are drawn to contrast. What looks like direct eye contact is more likely a baby studying the edge of a face or the shadow of an eye socket. Babies love looking at other human faces, but even something as simple as a brown ceiling fan against a white ceiling might hold their attention. A view of a blue sky through dark tree branches can be fascinating. The fad of buying black and white toys and clothing was a response to evidence that infants enjoy contrast. But it was just that: a fad. Any contrasting color scheme will do, and there are plenty available in every home and the great outdoors.
Scientists, until recently, have greatly miscalculated what the world feels like to infants. In what seems like lore from the dark ages of medicine, as recently as 15 years ago most doctors believed that newborns didn’t feel pain the way adults do. Nurses lanced their heels, drew blood, gave injections and inserted IV tubes; doctors even performed surgery on infants with no attempt at pain control. Today, the American Academy of Pediatrics has guidelines to assure that pain control is part of any medical procedure, no matter how young the baby.
The newborn’s sense of touch has been influenced for 40 weeks by the warmth of amniotic fluid and the secure confines of the uterus. Swaddling, cuddling and stroking can mimic that comfort as the infant gets used to being in the world. Simple human touch, especially bare skin on bare skin, releases brain chemicals that can calm an infant. (On the other hand, trauma can release neurochemicals that can set a child up for future trouble.)
We know that infants come into the world needing our undivided attention, our immediate response to their needs, and our undying love. What recent science is uncovering is that, though they are born utterly dependent, they also arrive remarkably ready to learn.
Susan Brink is a freelance medical writer. Her book, “The Fourth Trimester: Understanding, Nurturing, and Protecting an Infant Through the First Three Months,” published by University of California Press, was released March 20, 2013.