Everything starts the day your mom’s egg meets your dad’s sperm. After 4 weeks, your little brain begins to form. From the day of that union of those two little cells, your tiny self has around 9 months in your mother’s womb, to develop a brain, internal organs, all the bones and the right muscles to best prepare you for the life you have ahead.
Learning is also a part of the process. Epidemiologist David Barker says that whilst developing inside our mother, we are receiving ‘postcards’ from the outside world. As our forming systems interpret these messages, they adapt to what they anticipate will wait for us once we are born.
The full story

Everything starts the day your mom’s egg meets your dad’s sperm. 4 weeks later, your little brain begins to form. Epidemiologist David Barker says that whilst developing inside our mother, we are receiving ‘postcards’ from the outside world. These postcards tell us if this world is dangerous or safe or if food is plentiful or scarce. Knowing nothing else, we learn from those messages. Let’s watch what we experience and learn inside the womb from the fetus’ perspective.
Month 1 (1st Trimester)

Only 24 hours alive, every bit of genetic information is already present in a single cell: from our hair color to our talent as a future pianist. Then we divide ourselves again and again… After around a week, we travel from the ovaries to the uterus, where we then undergo the great divide, splitting into two. Half of which will become us, while the other half forms the placenta, which brings us food and oxygen and carries away waste. By week four, we have developed into a small being that is growing at a rate of 1 million cells per second. Our spinal cord, heart and brain are now clearly visible even if we are just the size of a poppy seed.
Month 2 (1st Trimester)

At about week 4 to 5, our heart starts to beat and we are now 10,000 times bigger than we were at conception. This is a crucial point in our neurological development, as our brain grows at a rate of around 100,000 cells each minute. If our mother consumes alcohol and drugs, or experiences extreme stress or trauma, our tiny brain can get damaged. This can lead to maths problems at school or even schizophrenia some 40 years later. If our mom stays healthy and can relax, our brain can develop to its full potential. We are now the size of a raspberry.
Month 3 (1st Trimester)

At the beginning of month three, we start to react to stimuli. Our sense of smell is developing and exposure to toxins can make us cringe. Our brain is continuing to grow very fast. Our ears start forming and we can soon hear our mom’s heartbeat and voice. Still small enough, we have plenty of space to move inside in the belly. Our mother’s womb becomes our sensory playground. We learn to move our arms, stretch our fingers, smile or suck our thumb. 75% of us are now showing a preference to use the right hand. We are now around the size of a lemon.
Month 4 (2nd Trimester)

Our head makes up about half our total size. We learn to kick, pee and how to swallow. Our taste buds are developing. If our mother eats a wide variety of things, we learn to appreciate different tastes and become less fussy eaters later in life. If we receive inadequate or poor nutrients, we adapt our physiology to sustain our development. This process is also called fetal programming. Some researchers have found that this can result in health problems such as obesity, heart conditions and diabetes later in life. We are now around the size of a big tomato.
Month 5 (2nd Trimester)

While earlier our mom’s voice sounded muffled, now it is starting to become clear. We are also experiencing a big growth spurt and we start the development of our teeth and our first real hair, fingernails, eyebrows, and eyelashes. We are becoming more active each day and enjoying flexing our tiny muscles. As we wriggle, kick and turn, our mother will start to feel us moving. If she responds, we learn that for every action, there is a reaction. We are now around the size of a dragon fruit.
Month 6 (2nd Trimester)

During this sixth month, a major mark of brain development occurs; our brain’s cerebral cortex splits into two hemispheres. But it’s also an exciting month for our eyes, which open for the first time. Even though we see only blurs, we start to respond to light. Some say it’s good if our mom now takes us into the sun. We are now starting to make simple facial expressions, such as forming a ‘grin’. We probably learn to communicate, for the time when we are born when we want to show our feelings. We are now around the size of a small cauliflower.
Month 7 (3rd Trimester)

We begin to develop regular intervals for sleeping and being awake. The hair on our head is now clearly visible and our milk teeth have formed under our gums. When we hear our mom speak, we may respond with an increased heartbeat and movement. Some researchers claim that we now begin to learn language from hearing voices from outside. Because once born, we seem to show a preference for our dad’s and mom’s native language. If we were to be born now, we would have a 90% chance of survival and arrive at the size of a pineapple.
Month 8 (3rd Trimester)

We are now behaving like a newborn. Our brain is functional and our nervous system ready. Our lungs are almost fully formed and we are practicing breathing by inhaling amniotic fluid. We now spend almost all of our time asleep, maybe dreaming about our near future. In preparation for birth, most of us will have now turned upside down. To get through that tiny hole at the end of the tunnel, our bones and skull are still extremely flexible. Only the immune system is still in its infancy. It will take many months after birth until our internal bodyguards can fully protect our health. We are now around the size of a melon.
Month 9 (3rd Trimester)

In the last month, we keep practicing our motor skills and kicks. When our Mom laughs, eats sweets or drinks an ice tea, we might respond by bouncing up and down. If we could already understand research papers, we would now hope that our mom can bring us to the world through natural birth, which protects us through a stronger immune system for life. The puzzle of what is nurture and what is nature is now well underway and already shows the first image of our character. The most important missing piece will be added in our early childhood. At the end of the 9 months, we are around the size of a jackfruit.

After many hours of hard labour, we will be welcomed into this world! Some will then be instantly taken away, for various check-up procedures and bathing. But if we are lucky, we will first spend some time with our mom. If placed on her belly, we will instinctively crawl to her breast and then show our sucking skills. This makes us happy, full and feel safe. The foundation for all future learning.
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Sources
- Interactive Prenatal Development Timeline – The Endowment for Human Health
- Prenatal origins of adult disease – a study by the University of Wyoming
- Resilience – and much more from Center on the Developing Child, Harvard University
- Read the full script here – by Sprouts
- Mali baby tracker and pregnancy symptoms by week (in English)
- Mali baby tracker and pregnancy symptoms by week (in Thai)
Dig deeper!
- How to Focus on Self-Care during Pregnancy – The Motherly forum
- Prenatal Risk Factors for Developmental Delay in Newcomer Children – Caring for kids new to Canada
- The long term effects of prenatal development on growth and metabolism – from the journal Seminars in Reproductive Medicine
- Fetal Health and Development – MedLine Plus
- Basics about Fetal Alcohol Spectrum Disorders (FASDs) – The Centres for Disease Control and Prevention
Classroom exercise
What advice would you give to your younger self? Have your class write their own “postcards from the outside world”. What is the most important thing you think your younger self should know? Include all of the tips and tricks to succeed that you’ve learnt so far. Or perhaps you would like to ask them a question. Let us know what your students include on their postcards in the comments below!