Bumpology is our weekly column on the science behind pregnancy, written by our reporter whose own bump is growing larger by the day
Days to go: 104
Waist size: 88 centimetres (34.5 inches)
Additional note: Rampant kicking – especially when I lie down to sleep at night
Throughout my pregnancy I've been pondering the question of consciousness – not mine, that of my fetus. Is she aware of her environment? Does she have a sense of identity? Can she think, or dream? And if she was born tomorrow, what could she know about the world around her?
Clearly these are difficult questions to answer, since scientists have yet to come up with a clear definition of what consciousness is in adults, let alone fetuses, who have no way of describing their experiences. However, the question has become still more pertinent this week, as I pass the UK's 24-week cut-off for abortion and sail towards my third trimester. This means that if my baby were born tomorrow, she'd be in with a fighting chance of survival – albeit with the help of a ventilator. Which raises the question: would she be conscious?
"Most doctors who look after preterm babies would say that they're conscious," says Vivette Glover, a fetal researcher at Imperial College London. One clue is that after around 26 weeks, premature babies seem to fixate on some objects – such as their mother's face – for longer than others, suggesting that they can perceive their environment and judge the relative importance of different things in it. The fetus also seems capable of responding to pain after 24 to 26 weeks.
The key issue seems to be when the peripheral nervous system joins up with the cerebral cortex, the region of the brain responsible for higher thought processes such as memory, attention, thought, awareness and language. "Without this kind of sensory input you can't be aware of your surroundings or pain or be conscious," says Hugo Lagercrantz, a neonatal researcher at the Karolinska Institute in Stockholm, Sweden. The joining of the cortex to the peripheral nervous system provides that vital link between the outside world and the higher brain. This should have occurred by about 25 weeks of pregnancy – or today in my case.
All of which begs the second question: what has been running through my baby's brain up until now?
From worm to reptile
By the end of the first trimester, when most women will see their fetus for the first time through an ultrasound scan, its neural circuitry is roughly on a par with that of an earthworm or a marine snail, says David Edelman, a consciousness researcher at the Neurosciences Institute in La Jolla, California.
The comparison is approximate: all we can say for certain is that by around 12 weeks, the fetus has peripheral circuits which enable it to perform reflex actions without any involvement from the brain.
So although I could see my baby moving around when I had my first scan, that doesn't mean she was consciously exploring. "At that stage there's no link between the neurons of the spinal cord and the brain," says Glover.
These connections start to form at around 17 or 18 weeks of pregnancy, when the fetus's level of consciousness might be roughly that of a reptile.
"A reptile responds to certain signals like a sight or the smell of a mouse, and there is some kind of pattern to these responses," says Lagercrantz. But reptiles do not possess a cerebral cortex, meaning they are unlikely to engage in higher thought processes like abstract reasoning.
Dozing towards birth
That's not to say my fetus is now questioning the meaning of life, or even making sense of the sounds she can now hear coming in through my belly. Indeed, the fetus remains for the most part sedated by low oxygen levels and anaesthetic chemicals that are produced by the placenta, says Lagercrantz.
Only when she is expelled from my uterus – which I hope won't be for another 15 weeks or so – will she fully "wake up" and experience the world for the first time.
Landmarks in brain development
7 weeks: First movements.
10 weeks: Some breathing movements and hand-face contact.
11 weeks: Yawning.
12 weeks: Sucking and swallowing.
14 weeks: Most of the body responds to touch, with the exception of the head and back.
16 weeks: Eye movements.
19 weeks: Fetus withdraws in response to "painful" stimuli. By 20 weeks, levels of the stress hormones cortisol and noradrenaline, and the natural painkiller beta-endorphin are released by the fetus in response to a needle being inserted into its abdomen.
22 to 24 weeks: Fetus starts responding to sounds. Some evidence of learning: if a sound occurs repeatedly, the fetus will eventually stop reacting to it.
24 to 25 weeks: Peripheral nervous system connects with the cortex, the brain region responsible for higher thought processes.
24 to 26 weeks: Begins to respond to pain. Able to survive outside the uterus with the help of a ventilator.
32 weeks: Established patterns of sleep including REM sleep (dreaming sleep), non-REM sleep and waking.
40 weeks: birth. The fetus is roused and takes its first gulps of air. It stays awake for approximately 2 hours, before falling asleep again.
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