The fetal nervous system — i.e. your baby's brain, spinal cord and nerves — is one of the very first systems to develop. In fact, it's making big strides before you even know you're pregnant.

When does a fetus develop a brain?

Fetal brain development starts probably before you even realize you’ve conceived. When you’re just 5 weeks pregnant, the first neural cells begin to divide and differentiate into neurons and glia (the two types of cells that form the nervous system). 

Also at about week 5 of pregnancy, the neural plate folds onto itself to form the neural tube, which closes by about week 6 of pregnancy to eventually become the brain and spinal cord. 

By about week 10, the brain is a small, smooth structure that looks a whole lot more like the brain you’re used to (minus the folds that make up the various brain regions, which develop later in pregnancy).

When does a fetus have brain activity?

The first synapses in baby’s spinal cord form during week 7 of pregnancy. By week 8, electrical activity begins in the brain — allowing your baby to coordinate his first (spontaneous) movements that doctors can even see on an ultrasound!  

Your baby’s brain continues to develop in the coming weeks, endowing him with a remarkable range of involuntary movements like stretching, yawning and sucking by the end of the first trimester and more coordinated movements in the second trimester. 

That said, the brainstem, which controls vital functions like heart rate and breathing, isn’t mostly complete until the end of the second trimester, and the cerebral cortex doesn’t take up its duties until the third trimester. 

In fact, the cerebral cortex — which is responsible for voluntary actions, thinking and feeling — only starts to work around the end of pregnancy, with simple electrical activity detectable in regions associated with senses (like touch) and motor skills in premature babies. 

Brain development timeline

There are five different regions of the brain that develop, each responsible for different functions:

  • Cerebrum: 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 the body that are responsible for growth, metabolism and more.
  • Hypothalamus: This area deals with body temperature, hunger, 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

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 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 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 move throughout the embryo to kickstart nerve development. 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 your baby's first synapses, which essentially means neurons can interact and create early fetal movements, like curling into 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 it quite yet. 

At about the same time as your baby first wiggles his limbs, he also begins to develop the sense of touch.

Second trimester

During the second trimester, your baby's brain is directing steady contractions of the diaphragm and chest muscles (think of them as preliminary breathing movements).

Baby's sucking and swallowing impulses will also get some practice. 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 that your baby's tasting, too, another sense that's amping up.

At around 18 weeks of pregnancy, you'll feel your baby's first kick! (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 will continue to grow until your baby's first birthday. And around 28 weeks, another big reflex occurs: blinking.

At the tail-end of trimester two, your little one's brainstem (controlling heart rate, breathing and 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 can detect 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

The third trimester is brimming with rapid development of neurons and wiring. His brain roughly triples in weight during the last 13 weeks of pregnancy, growing from about 3.5 ounces at the end of the second trimester to almost 10.6 ounces at term. 

Your baby’s brain is starting to look different, too: Its 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 (chiefly responsible for 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 (the part responsible for thinking, remembering and 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 your baby's enriching environment.

What food is good for your baby’s brain?

Because your baby's nervous system starts developing right out of the gate, it's important to consume 400 micrograms of folate (aka folic acid or vitamin B9) daily before getting pregnant and up that amount to 600 mcg once you do. Ideally, aim to start taking prenatal vitamins about three months before trying to conceive. 

Folate is essential for fetal cell growth, tissue development and DNA. Consuming enough before (and early in) pregnancy reduces a baby's chance of serious neural tube defects (like spina bifida) by 70 percent. Research also suggests that consuming enough of the nutrient can reduce the chances of 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 your 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 sardines), along with DHA-fortified eggs. If you’re vegan, talk to your doctor about whether you should take algal oil supplements to boost your DHA intake.

When does the brain stop developing?

Your baby’s brain will continue to mature throughout childhood — with researchers estimating that the brain only stops developing around age 25! 

During the first three to five years of your little one’s life, the brain develops rapidly. By the age of 9, all of the major structures are in place. 

That certainly doesn’t mean brain development is done. The prefrontal lobe is the last area of the brain to develop, starting during the teen years. The prefrontal cortex plays an important role in what you might call “adulting” functions: goal-oriented decision making, memory encoding and retrieval, language and even intelligence. Until it’s fully developed, the amygdala (the part of the brain responsible for gut reactions like fear) tends to drive decision-making.

Throughout pregnancy and well beyond, your baby’s brain develops at an astonishing pace, from a collection of cells to a fully-functioning decision-making center. You’ll be thrilled when you feel those first fetal movements initiated by your baby's brain — and enamored when it connects those little eyes with yours for the very first time.