Fetal development: Your baby's brain

Fetal development: Your baby's brain

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It's probably no surprise that your baby's brain is one of the first major organs to start developing. But you may not know that it will continue to grow until she's in her early 20s!

Together, the brain and the spinal cord make up the central nervous system. The brain is enclosed within the skull, and the spinal cord is encased within a flexible spinal column made up of 33 separate bones (vertebrae). A network of nerves branches off the spinal cord, and these nerves send signals to and receive information from various organs.

Early development of the brain

The first part of this system appears just three weeks after fertilization as an oval-shaped disk of tissue called the neural plate. At this early stage of development (5 weeks pregnant), your baby is an embryo that looks like a tiny tadpole, with the neural plate running down the middle from head to tail.

Over the course of this week, the edges of the plate rise and fold toward each other, forming the neural tube that will become your baby's spinal column and brain. At this point, the ends of the tube remain open, and the brain starts to take shape at the top of the tube. Near the bottom is the structure that will eventually become the tailbone (coccyx).

By the time you're 6 weeks pregnant, the neural tube is completely closed at both ends, and at the top of the tube, the brain consists of three areas:

  • The forebrain develops into the cerebrum, which directs higher brain functions, like thinking and problem-solving.
  • The midbrain contains the structures involved in processing visual and auditory information.
  • The hindbrain develops into the cerebellum, which manages balance and coordinates motor and sensory functions, as well as the medulla, which is the control center for the body's automatic processes, like blood pressure and heart rate.

Cavities called ventricles also have formed. These produce the cerebrospinal fluid which allows the brain to "float" within the skull and acts as a shock absorber.

How the nervous system develops

Located along the edges of the developing neural tube is the neural crest. This crest, along with the brain and spinal cord, give rise to the millions of nerves that branch out all over the body. Nerves send back sensory information to the brain and spinal cord for processing and relay the motor information that signals to muscles and organs how and when to act.

From 8 weeks of pregnancy on, these nerves are making connections not only with each other, but also with muscles and other tissues as well as organs, like the eyes and ears. At 12 weeks, the nerves start sending out simple signals that cause reflex behaviors. For example, your baby's fingers can open and close, and her toes can curl. She can also squint her eye muscles and make sucking movements with her mouth.

By about 28 weeks, nerves connect with their designated organs so your baby's senses of hearing, smell, and taste can begin to function. Some nerve cells develop a sheath of insulating material called myelin that speeds up signaling between nerves. Myelin starts to form in the third trimester and continues after birth and well into adulthood.

Although brain development takes place throughout pregnancy, it really kicks into high gear in the last trimester as the brain triples in weight. During these final weeks, the cerebrum also develops deep, convoluted grooves that provide extra surface area without taking up more room in the skull. This wrinkly outer layer is known as the cerebral cortex.

Your baby's brain at birth

How well does your baby's brain function at birth? Your newborn arrives equipped with all kinds of fascinating abilities that reflect the amazing growth from tiny neural plate to full-fledged nervous system:

  • She'll have a wide range of reflexes that you can even test yourself. For example, if you stroke her cheek, she'll turn her head toward you (rooting reflex). Put your finger in her mouth, and she'll automatically begin to suck (sucking reflex). When you hold her upright with her feet touching the floor, she'll make little stepping movements (stepping reflex).
  • She can recognize your voice! Starting around the third trimester, your little one can eavesdrop on your conversations, and by the time she's born, she'll show a clear preference for your voice over others. She'll even turn her head when she hears you.
  • Although you might imagine that your baby would be just as interested in looking at her teddy bear as she would at you, research shows that babies are especially attuned to human faces, preferring them to random designs.

And keep in mind that because your baby's brain continues to grow after birth, every day new neural connections form between the different parts of her brain, adding to her growing store of knowledge, memory, and experience.

What you can do during pregnancy

  • Take a folic acid supplement during (and even before) pregnancy. Folic acid is a B vitamin that's crucial to the development of the brain and spinal cord. Getting enough folic acid greatly reduces your baby's risk of neural tube defects like spina bifida and anencephaly. The neural tube develops very early (even before many women even know they're pregnant), so experts recommend that you take 400 micrograms of folic acid daily at least a month before you start trying to get pregnant. You can get it from a prenatal vitamin or take it as a separate supplement.
  • Eat cooked fish 2 to 3 times a week. Fish – especially fatty fish like salmon – contain omega-3 fatty acids, which research suggests boosts your baby's brain development during pregnancy and into childhood. See our article on how to choose fish that's rich in omega-3's but low in mercury and other contaminants, which can harm a baby's developing nervous system.

Key milestones in fetal brain development

Weeks pregnantMilestone
5 weeksThe neural plate forms.
6 weeksThe neural tube forms and closes. The brain is now made up of three areas (forebrain, midbrain, and hindbrain), and the ventricles have formed.
8 weeksA network of nerves starts to extend throughout the body.
12 weeksFetal reflexes are present.
28 weeksSenses of hearing, smell, and touch are developed and functional.
28 to 39 weeksThe brain triples in weight, and deep grooves develop in the cerebrum to allow more surface area for brain neurons. Myelin starts to develop along some neural pathways.

Watch the video: Learn how to boost your babys brain from a Harvard Professor. UNICEF (May 2022).

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