Funny faces, heart-warming giggles and thunderous farts - if you have spent any time watching a baby grow and develop, you’ll know that they can do some weird things at times.


But don’t for one moment think that it was only after they were born that they got up to their unusual antics - they were up to all sorts of strange behaviours while they were still in the womb. Here are a few things that you definitely did while you were still in utero:


You invaded your mother’s body

One week after conception, you transformed into a tiny, fluid-filled sac that attached itself to the thick, sponge-like membrane in your mother’s womb. Soon after, the sac began to burrow deep into the membrane.

At this point, the whole scene resembled a gory horror film. Cells dying in their masses, burst blood vessels everywhere! The invading cells sprout small roots that paralyse your mother’s blood vessels and rebuild them according to their own needs. This is how the placenta begins taking shape.

© Juliana Gómez

Through this organ, your mother delivers all the nutrition and fresh oxygen you need to grow, and all your waste material is sent back to her in return.

However, waste is not the only thing you delivered back. Some of your cells also passed over to your mother. Blood tests have shown that mothers carry cells from their children many decades after pregnancy. Stem cells from the foetus can even find their way to its mother’s heart, where they turn into pulsating heart cells to help repair damage.

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So even though we start off as brutal invaders, we can be a little helpful in the womb as well.


You grew a tail

By the start of week five it was impossible to see that you were going to become a human being; you looked more like a prawn. Your tiny, transparent body curled up with your head bowed down towards a long tail. Later, the tail disappeared, leaving only the bony stump that hurts when you fall on your bottom. So why bother growing a tail in the first place?

Study the embryo of a lizard, a chicken or an elephant, and you will find the same prawn-like creature. This basic form is organised by genes inherited from our common ancestor, who roamed the vast primitive ocean hundreds of millions of years ago.

Essentially, we are all reconstructed fish. Bear this in mind, and many seemingly illogical facts about your body suddenly start making sense.

Hard labour: the case for testing drugs on pregnant women © Laura Breiling

Take the small vertical groove that runs from your upper lip to your nose. It doesn’t really serve any specific purpose, it’s simply a result of the cumbersome way our faces are formed. To begin with, your face consists of three separate parts; your eyes sit on either side of your head just like a fish, and your nostrils sit right on top.

Then each part begins to move around slowly, towards the same point; your nostrils creep down from your forehead and your eyes move round towards the middle. Eventually, all these parts are woven together on a point just below where your nose is today. The only evidence remaining will be the little vertical groove – a reminder of a time when you looked completely different.


You shaped your fingers by mass cell suicides

About the same time as your tail appeared, little shoots grew on each side of your body, which would eventually become your arms and legs. The wings of a chicken or the massive legs of a hippopotamus start off in exactly the same manner. Even whale embryos exhibit similar looking shoots, despite the fact that they grow neither arms nor legs; instead their forelimbs turn into flippers, while all that remains of the hindlimbs are a few small bony stumps.

In your case, the shoots grew outwards until they look like tiny paddles. At first, your fingers are webbed, but in week eight, they become separated. This transformation occurs through well-coordinated mass cell suicide.

Could we design babies, if there were no ethical constraints? © Getty Images

It all starts when your future finger cells send out death signals. As soon as their neighbours receive these signals, they begin to degrade their proteins. The DNA strands, which the cells would normally do everything to protect, get sliced up into tiny pieces by scissor proteins.

Everything gets destroyed. In the end, there is nothing but crumpled bags of remains left behind. Scavenger cells wander around mopping up the waste, so that the space between the fingers can be cleaned up and gradually, one cell death at a time, the paddle becomes a living hand.


You drank your own urine

Yes, you read correctly. About 10 weeks after conception you started drinking foetal water and peeing it out again. In other words, you spent several months bathing in your own urine, and as if that wasn’t enough, even drinking from this polluted swimming pool.

However, what you were doing was both vital and ingenious, and nowhere near as disgusting as it first sounds.

First of all, your mother made sure your watery home was regularly cleaned by letting the waste sift out of the foetal water and into her blood. Second, your organs were given some badly needed practice. Your kidneys, which actually took you three attempts to build, start filtering blood and producing urine.

Is it possible to get pregnant when you’re already pregnant? © Getty Images

At the same time, you prepared for one of the most important things you will do after you are born: drinking milk. While your intestines were busy absorbing nutrients from the foetal water, your cheeks grew chubbier and your sucking muscles developed.

You might even have trained your taste buds. Everything that enters your mother’s blood can end up in your underwater home, and that includes flavours from the food she eats. Researchers who sniffed samples of foetal water taken from different pregnant women could easily tell who had been eating garlic, and babies seem to prefer foods that their mother ate regularly during pregnancy.

One sip at a time, we prepare ourselves for life on the outside.


You overproduced nerve cells

Your nerve cells didn’t get an easy start. Born from stem cells deep within the brain, they set off on a winding journey towards their new home.

The brain constructs itself from the inside out, layer by layer, and the deepest, most primitive areas of the brain are formed first. The outermost layer, responsible for the most advanced brain functions, develops at the end of foetal development. In order to reach the outer parts of the brain, the nerve cells latch on to supporting cells that sprout long tendrils right through the brain layers and climb like tiny snails moving up a blade of grass.

In the end, the nerve cell finally reaches its new home – but that is when the real challenge begins. Long fibres grow out from nerve cells in all directions: these are the literal wires of your nervous system. Each cell needs to connect to the right place, so that they can communicate with sensory cells, muscles or other nerve cells.

As soon as the fibres reach their target, they pick up a protein message and send it back to the core of the cell to switch on the genes that will secure the cell’s future. If the message doesn’t arrive in time, the cell will assume that it never succeeded in connecting to the target and die, shrivelling up into a floppy bag just like the cells between your fingers did.

In fact, this unhappy fate awaits many of your nerve cells because you produce too many of them. The nerve cells are in competition with each other, and only those that make the best connections survive. Many nerve cells sacrificed themselves to make your brain as good as it is.


Despite it being one of the first organs you start constructing, your brain is the last to be finished. In fact, you can never say that it’s completely finished. Everything you learn and remember leads to physical changes in the connections between your nerve cells. By the time you finish reading this article, your brain will be slightly different from when you started. Your brain is your life project.

The Making of You: A Journey from Cell to Human by Katharina Vestre is available now (£10.99, Wellcome Collection)