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Brain Development in Fetus

Updated: Apr 9, 2023

Article By Sucharita Desu

Brain development is a complex process. It starts when a baby is conceived and continues all throughout pregnancy. To understand the gist, an embryo’s brain and nervous system begin to develop at around the 6-week mark. The brain starts to carry out functions soon after and develops some major parts cerebellum, brain stem, and hypothalamus. Once the baby’s born, the brain is fully functional and ready to grow in the real world.

In the first trimester, the embryo forms a neural plate a couple of weeks after the baby’s conception. This neural plate is the base for the nervous system. As it grows and becomes longer, it folds in on itself to become a neural tube. This happens from the first month to around 6 weeks (about 1 and a half months). At one end of the tube, there is a bulge which becomes the brain, while the rest stretches and develops into the spinal cord and the rest of the nervous system. The brain also splits into three parts at the same time, the front brain, midbrain, and hindbrain. Eventually, these parts become more specialized parts of the brain.

From around week 7, once the neural tube is completely closed, the brain grows rapidly. In fact, the growth rate of the brain is around 250,000 neurons per minute! This rate stays the same for about another 21 weeks (until around week 28) before slowing down. As the brain grows millions of neurons, it also begins to connect synapses to direct movement and growth. Eventually, the brain will start sending out electric impulses to the rest of the body to carry out tasks. At as early as 8 weeks (about 2 months), you can see physical evidence of the brain working (the electric impulses) as ultrasounds show the embryo moving.

A cool fact about the brain during the first trimester is the brain makes up half the fetus’ weight! To compare, when a baby is born, the brain makes up only 10% of its weight.

In the second trimester, the fetus’ brain starts to control the compression of its chest muscles and movement of its diaphragm. These movements are controlled by the brain stem and allow the baby to practice breathing. In addition, at around week 16, the fetus begins to gain control over swallowing and sucking. By week 21, the fetus can properly swallow amniotic fluid. At the same time, the baby starts to test out other movements controlled by the cerebellum including kicking and stretching. In this trimester, the baby’s brain stem has almost entirely developed, and the nervous system is developed enough to detect loud noises. Babies can even identify voices while still in the womb at this point! Lastly, a fetus also sends out brain waves during sleep, indicating that babies experience sleep cycles that include REM sleep (stage of dreaming), even before being born.

In the third and final trimester, the brain of the fetus triples in size, growing from 3 ounces (about 85.05 g) to almost 11 ounces (about 311.84 g). The cerebrum also develops groves and ridges, and the brain separates into the left and right brain. Fun fact, the fastest growing part in the third trimester is the cerebellum, which is responsible for motor control. Thus, this is also the trimester where the baby begins to move more, from wiggling its fingers and toes to stretching and kicking. Plus, the fetus’ sensory system begins to show integration and functionality in the third trimester.

As you know, our brain has separate parts responsible for different things. Some of these parts are developed after you are born, but the basis of it is developed in the womb. These parts are:

  1. Cerebrum; it is the largest part, contains the cerebral cortex and frontal and temporal lobes, and is responsible for thinking, feeling, and memory.

  2. Cerebellum; it directs body motor control.

  3. Brain stem; it oversees vital functions, mainly involuntary, like heart beating, blood pressure, and breathing, as well as the digestive process.

  4. Pituitary gland; it releases hormones in the body.

  5. Hypothalamus; it is responsible for regulating body temperature, hunger and thirst cues, sleep, and emotion.

To help babies and fetuses to grow and develop healthy brains, it is important to take necessary precautions. This includes eating a balanced diet, drinking plenty of water, as well as having enough folic acid and omega 3 fatty acid intake. Sources of harm to brain growth include alcohol consumption, smoking, illness, and infection in the mother, and cleaning a cat’s litter box - because feline feces can contain dangerous parasites.

It is important to note that the development process does not end here - at birth. Studies show that your brain keeps growing, changing, and developing until you are around 25 years old. Such a lengthy process takes a lot of time to understand, however, there are stages that can be studied separately based on age or type of brain development. We encourage you to investigate the development of the brain more using these links, as well as your own research:

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