Last updated on Feb 17th, 2021 at 11:08 am

How the brain develops stage by stage

The development of the brain starts with the genetic material handed down from the parents, says Prof Lorna Jacklin, a neurodevelopmental paediatrician: “A genetic programme deterimines how the brain develops.”
There’s interplay between genetics and environment from the earliest stage. A baby may be born with a predisposition to a genetic weakness that may never present as a problem; if the environment is not optimal, the genetic weakness can be brought to the fore. She explains: “Many conditions, such as autism, ADHD and Foetal Alcohol Syndrome are multifactorial conditions. They’re not caused by a pure genetic abnormality, but by a predisposition, combined with environmental factors. So if there is a genetic predisposition to Foetal Alcohol Syndrome, for instance, even a very small amount of alcohol may cause it. Another woman can drink more, but her child will be unaffected.”

Brain development in the first trimester

During the first trimester, the central nervous system is developing rapidly. In the very early weeks of pregnancy, the neural tube develops, which eventually becomes the brain and the spinal cord. The brain develops into distinct areas and is already highly complex by the end of the first trimester.
This is an important and risky period for brain development, Prof Jacklin says, “Neurons are migrating to where they have to be, so this is a very sensitive period. A fever, flu, radiation and certain medicines can have a damaging effect.” Women don’t always know they are pregnant, and may unknowingly indulge in risky behaviour in those early weeks.

Second trimester

The brainstem – the part of the brain responsible for essential functions such as breathing and the sucking reflex – is largely mature by the end of this trimester.
“At this stage, and in fact for the first two years of life, your baby’s brain is developing the synapses, the connection between the neurons,” says Prof Jacklin. “What’s important now is that there is a healthy placenta, and the baby is getting enough oxygen and nutrition.” You can’t ‘stimulate’ your baby’s brain at this stage.

Third trimester

In the third trimester, there is apoptosis – ‘pruning’ of the brain. Prof Jacklin explains: “The brain develops too many brain cells. After neuronal migration, when the neurons go to where they need to be, the brain selects the most important cells, and those that aren’t required die off. This results in faster, more efficient connections.” The over-development of brain cells is important, because it’s the basis of ‘plasticity’ in the brain and allows the brain to compensate for early damage. Prof Jacklin says: “If there’s a brain bleed at 20 weeks, other parts of the brain can actually take over the function of the part of the brain that’s damaged. I’ve seen babies where an X-ray shows a hole in the brain, and you would expect brain damage, but other parts of the brain have compensated.”
The last part of the brain to mature is the cerebral cortex. This is the part that’s responsible for thinking, remembering and feeling. In other words, for consciousness. It has begun to function by the time the baby is born, but is still primitive and it continues to develop and mature throughout childhood.

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The best start for baby’s brain

  • Get antenatal care as soon as you’re pregnant. It’s essential in identifying and preventing underlying health problems.
  • Take your folic acid. It’s the best thing you can do to prevent neural tube defects.
  • Eat well. Under- nourished moms tend to produce smaller, malnourished babies, and brain size is roughly associated with brain power, says Dr Medina, author of best-selling Brain Rules for Baby. There’s also evidence to suggest that a mom’s diet influences her unborn baby’s taste preferences. So eating a healthy, varied diet with plenty of vegetables may also result in your baby being more open to those flavours and more likely to follow a healthy diet.
  • Manage your stress. Scientists have researched extremely stressful situations, such as cases where the father had died while the baby was in utero, or where the mother was affected by a natural disaster, to study the effects of extreme maternal stress on the unborn child. Stress hormones such as cortisol and adrenaline do reach your baby, where they may contribute to problems in behaviour and attention, and even affect cognitive development.