Fetal Nervous System and Brain
The fetal nervous system — i.e., your baby-to-be’s brain and spinal cord — is one of the very first systems to develop. In fact, it’s making big strides before you even know you’re pregnant.
THE PARTS OF YOUR BABY’S BRAIN
Before we get into the science of fetal brain development, here’s a quick anatomy primer on your baby’s brain. There are five parts, each responsible for different functions:
Cerebrum: This is the biggest part of the brain, and it’s responsible for thinking, remembering and feeling. This is where the cerebral cortex and its various lobes (including the frontal and temporal lobes) reside.
Cerebellum: The area in charge of motor control.
Brain stem: The engine driving many of your baby’s most vital functions, including heart rate, breathing and blood pressure.
Pituitary gland: This pea-sized gland releases hormones into your body that are responsible for growth, metabolism and more.
Hypothalamus: This area deals with body temperature, hunger and thirst, sleep and emotions.
With the biology lesson out of the way, read on to find out how and when these various parts start developing.
FIRST TRIMESTER: BABY STARTS MOVING
A mere 16 days after conception, your fetus’s neural plate forms (think of it as the foundation of your baby’s brain and spinal cord). It grows longer and folds onto itself, until that fold morphs into a groove, and that groove turns into a tube — the neural tube. Once the neural tube closes, at around week 6 or week 7 of pregnancy, it curves and bulges into three sections, commonly known as the forebrain, midbrain and hindbrain. Just to the rear of the hindbrain sits the part that will soon turn into your baby’s spinal cord. Soon, these areas bubble into those five different regions of the brain that we’re most familiar with: the cerebrum, cerebellum, brain stem, pituitary gland and the hypothalamus. Of course, all of these fetal brain areas need more time to be fully up and running!
At the same time, special neural cells form and migrate throughout the embryo to form the very beginnings of nerves. Your baby’s nervous system is made up of millions upon millions of neurons; each of these microscopic cells have itty-bitty branches coming off of them so that they can connect and communicate with each other. With this comes baby’s first synapses, which essentially means baby’s neurons can communicate and create early fetal movements...like curling into (you guessed it!) the fetal position.
Other movements follow quickly, with your fetus wiggling his developing limbs at around 8 weeks. By the end of the first trimester, your baby-to-be has garnered quite a repertoire of motion, though you won’t be able to feel any of it quite yet. And at about the same time as baby first wiggles his limbs, he begins to develop the sense of touch.
SECOND TRIMESTER: BABY SUCKS, SWALLOWS, BLINKS AND DREAMS
During the second trimester, steady contractions of baby’s diaphragm and chest muscles occur (think of them as practice breathing movements). Baby’s first sucking and swallowing impulses kick in around 16 weeks. By 21 weeks, your baby’s natural reflexes will allow him to swallow several ounces of amniotic fluid every day. And all of that swallowing means baby’s tasting, too – another sense that’s now in full gear.
At around 18 weeks of pregnancy, you’ll feel baby’s first kick (but don’t worry if it takes a few weeks longer — that’s common, especially among first-time moms). Around the same time, your baby’s nerves become covered with myelin, a protective insulation that speeds messages between nerve cells (myelin continues to grow until your baby’s first birthday). And at 24 weeks, another big reflex occurs: Blinking.
At the tail-end of trimester two, your little one’s brainstem (heart rate, breathing, blood pressure) is almost entirely mature, resting just above the spinal cord but below the cerebral cortex (the last area to mature). By now, the fetal nervous system is developed enough so your baby is startled by loud noises outside the womb — and may even turn his head toward the sound of your voice! Another exciting development: At 28 weeks, fetal brainwave activity features sleep cycles, including REM (the stage when dreaming occurs).
THIRD TRIMESTER: BABY’S BRAIN GROWS
The third trimester is brimming with rapid development of neurons and wiring. Baby’s brain roughly triples in weight during the last 13 weeks of gestation, growing from about 3.5 ounces at the end the second trimester to almost 10.6 ounces at term. And it’s starting to look different, too: Its formerly once smooth surface is becoming increasingly grooved and indented (like the images of brains you’re used to seeing).
At the same time, the cerebellum (motor control) is developing fast — faster now than any other area of the fetal brain (its surface area increases 30-fold in the last 16 weeks of pregnancy!).
All of this growth is big news for the cerebral cortex (thinking, remembering, feeling). Though this important area of the brain is developing rapidly during pregnancy, it really only starts to function around the time a full-term baby is born — and it steadily and gradually matures in the first few years of life, thanks to baby’s enriching environment.
EATING TO SUPPORT BABY’S BRAIN DEVELOPMENT
Because your baby’s nervous system starts developing right out of the starting gates, it’s important to consume 400 micrograms of folate (aka folic acid or vitamin B) daily as soon as you think you might want to get pregnant. This nutrient is imperative for fetal cell growth, tissue development and DNA — and consuming enough before (and early in) pregnancy reduces a baby’s chance of serious neural tube defects (like spina bifida) by 70 percent. Emerging research in the Journal of the American Medical Association also suggests that the nutrient can reduce the chances your child will be born with an autism spectrum disorder by up to 40 percent. So take your prenatal vitamin (which should have at least 400 mcg), and make sure to eat plenty of folate-rich foods (like leafy greens and whole grains).
Another important nutrient for brain (and eye) development: omega-3 fatty acids, specifically DHA (aka docosahexaenoic acid). Getting enough — especially during your third trimester, when baby’s brain is developing the fastest — is vital, since it’s a major structural fat in the brain and eyes. The good news: DHA is found in lots of safe-to-eat fatty, cold water fish (like salmon, trout and cod), along with seaweed and DHA-fortified eggs.
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