We started the series by considering the first 98 days of your stay in the womb – how you passed your first test, began to show a preference for either or both your hands, and how your fingerprints were formed as you pushed your fingers against the amniotic sac that served as a cushion and shock absorber for you.

In the concluding part of the series, we shall be considering the last 168 days of your stay, and what effects they had on you.

Week 15 – Your Sex is Finally Decided

By now you had male or female genitals, determined by the size of a dose of testosterone at eight weeks. Now a second dose helped shape your brain.

From 15 weeks, male foetuses receive a big surge in testosterone, created in their testicles. Female foetuses receive a much lower dose from their mother and their adrenal gland. Around this time, aspects of your personality were being connected in your brain.

Exposure to high levels of testosterone is thought to contribute to more ‘male-type’ behaviours like risk-taking. Curiously, people exposed to higher testosterone in the womb also have a longer ring-finger relative to their index finger.

Week 28 – Your Eyes are Ready to Take On the World

A foetus is well developed by 28 weeks – the start of the third trimester. By 28 weeks your brain and body were well developed, so you were almost ready to see the world at first-hand.

Two eyes lined with colour-sensing cone cells had developed. Pigments that could detect short (blue), medium (green) or long (red) wavelengths of light were being produced.

Most people can detect 10 million different colours once born. But 8% of males and 0.5% of females are born colour-blind, without all the necessary pigments. Some people are born with a fourth type of pigment that senses wavelengths between red and green, so they see colours even more vividly.

Week 37 – The Countdown Begins to Welcome You into the World

Over nine months you had grown from one cell to a trillion or so. Your size at birth depended on many things, including your race, gender and genes.

But external factors like your mother’s diet, stress levels and smoking status also played a role. One emerging idea is that the environment in your mother’s womb might have changed chemical markers within your DNA that control how your genes were switched on and off as you grew.

Evidence suggests your birth weight might impact aspects of your health later in life, such as body mass index, risk of diabetes and cognitive performance. Your time in the womb left its long-lasting mark on you.

That you are reading this means you made it. Welcome, special one!

See Also: The First 98 Days in Your Mother’s Womb that Shaped Your Identity

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