Newborn humans are born in a very undeveloped stage compared to other mammals. This is because if they stayed any longer in the mother, their head would become too big to fit through the birth canal. However, the advent of artificial womb technology has brought many changes to human development. As well as freeing many women from risk and providing for safer delivery, it has also allowed for the extension of the gestation process. This has introduced what is known as a "4th trimester", with a growing fetus spending 12 months in the machine and being decanted later than traditionally.

How would this affect child development of a growing fetus, as well as parenting in general?

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    $\begingroup$ We would need to coin the term "quadramester." $\endgroup$
    – cobaltduck
    Jul 27, 2019 at 1:47
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    $\begingroup$ @cobaltduck It's called a quarter. $\endgroup$
    – Brythan
    Jul 27, 2019 at 2:40
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    $\begingroup$ @cobaltduck: A trimester is a period of three months, as a semester is period of six months. Both are Latin words, borrowed into English (through French) with little change. Tres (three) + mens- ("month") + -ter (adjectival suffix) = trimester "three months" (attributive). $\endgroup$
    – AlexP
    Jul 27, 2019 at 6:24
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    $\begingroup$ I have to make a frame challenge here - without genetically altering the child being grown in the artificial womb, attempting to prolong the pregnancy much beyond 40 weeks is highly likely to result in infant mortality when the aging placenta dies and decay products poison the child. So, a fourth trimester of pregnancy for unaltered humans is not actually possible. $\endgroup$
    – Monty Wild
    Jul 27, 2019 at 7:33
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    $\begingroup$ Not just the head that's a problem. Someone who is overdue really doesn't have much more internal space to spare... jamming more weight and volume in that limited space, and keeping it there for several months, is going to be pretty physically punishing or even crippling all by itself. Regular pregnancy is quite bad enough. If it were only the head that was the problem, a caesarian section would take care of that issue. $\endgroup$ Jul 27, 2019 at 9:23

4 Answers 4


TL;DR: the effects of 4 trimesters are minimal, the effects of exowombs are large. I talk about the latter below the fold, if you cared

How would this affect child development of a growing fetus

Probably not a whole lot. Three months brings in some big changes relative to a newborn, but this will be dramatic stuff like "can support own head" and "can roll over".

The first requires sufficient strengthening of the neck muscles, which is presumably intrinsic in other species which can walk from birth, but it is quite possible that in humans muscle growth is left until the baby is on the outside to lower the nutritional demands on the mother. In the absence of those strengthened muscles you've still got a floppy baby just one with an even larger head that will require even stronger muscles to hold up.

So, genetic modification number one: boost muscle growth in the womb.

The second requires a certain amount of muscular co-ordination, probably the rudiments of balance, and the desire to actually roll around. Babies don't have to see and hear things to want to interact with them (congenitally blind and deaf children often have some developmental issues, but these don't have to be major). Adding rolling reflexes to a newborn is non-trivial. Obviously it can be made genetic (because other species can walk from birth, etc) but that sounds like quite a complex combination of genetic effects which may end up being harder to arrange than artificial wombs themselves.

Genetic modification number two: improve innate muscle control.

Everything else really requires exposure to the real world to stimulate brain development, gut flora development, balance, muscular control (unless you can fix that one) and so on.

Notably, your 4-trimester newborns will probably not be able to recognise the faces of their parents, unlike most regular children at the age of 3 months. This may or may not have developmental and bonding issues, but it will certainly have an effect on both the child and its parents.

edit: A comment above referenced placental breakdown... the organ isn't really designed to last longer than a regular pregnancy, so you could use your genetic engineering chops to improve its longevity. Practically though, you might just skip the need for placentas at all. They're designed to hook up with a regular womb (which your exowomb may not be) and to keep the two circulatory systems separate. You've only got one circulatory system to deal with, so you could just hook the foetus up to a combination ECMO, haemodialysis system (and possibly an artificial liver; not sure on that) and suitable nutrient exchange membranes and avoid the disposable meat components entirely.

Most of the interesting stuff is kinda secondary to the development itself, and are general potential benefits of exowombs.

It'd help the economy a little, because external child bearing would have little to no impact on the productivity of mothers right up to the decanting date. In fact, as they'd be under far fewer restrictions to their activities, they'd probably spend more as well as do more.

It'd have substantial health benefits of many kinds, because medical treatments for pregnant mothers are very limited, because no-one is prepared to take the ethical gamble of experimenting on them (everyone remembers thalidomide, right?). No restrictions on pharmaceuticals (up until the end, assuming they're going to breastfeed) and no restrictions on scanning techniques (because the foetus is in a separate warehouse, well away from the source of radiation).

Many early and indeed later developmental and physiological issues in children are associated with the health and nutrition of the pregnant mother, and those issues will go away. No non-genetic diseases can be spread to the child during the "pregnancy". Nutrition will always be perfect. It will be easy to supply minimum and safe amounts of common allergens (like peanut metabolites) which is believed to reduce the chance of developing fatal allergies later in life.

Pre-birth developmental issues will be easier to spot, because the scanning techniques don't need to deal with the problem of the mother being over the top. You might even be able to make visible light observation of the foetus routine if you wanted and it turned out to be useful. It might even be practical to do pre-birth surgery to deal with some problems like cleft palates and so on.

Childbirth will obviously be safer for all concerns. Maternal mortality will be zero, and the child is very unlikely to have problems due to birthing complications (it'll be a like a breadmaker, right? It goes ding, you open the lid and empty the contents out. Easy.)

There's some talk about exposure to vaginal secretions during birth being important for priming gut bacteria or dealing with immune issues in later life; if that turns out to be true I bet you can replicate the effect with a spoonful of carefully cultured yoghurt applied at decanting time. It certainly beats the possible negative effects of exposure to harmful microorganisms on the way out.

Vat-born children therefore have a good chance of being healthier than their peers (all else being equal), something that the traditional-birth-is-the-best nobility of your previous question would do well to remember.

Women who never give birth tend to have a different range of health risks in later live to mothers, but that's a separate issue. Avoiding the very real range of potentially serious, debilitating and long-lasting complications of pregnancy and childbirth is likely to make women opting for the exowomb approach healthier and happier too... again, something that your previous question's noblewomen might do well to remember.

as well as parenting in general?

It'd be a lot more appealing for people who didn't want to have a living organism burst out of their body, Aliens style.

Some people might worry about "bonding" with the baby, but to be honest... fathers can cope OK bonding with a child they haven't carried, and not all mothers bond with a child they did carry.

An extra three months isn't a big difference otherwise.

If the exowomb is fixed (in the sense of "immobile") then some of the standard ways of comforting a baby (like jiggling them up and down gently, or holding them and walking around) may well be less effective or entirely ineffective. This could be bad news for anyone who likes their sleep.

It is possible that the availability of exowombs will increase the number of children, because it will remove a number of issues associated with infertility, it removes the health risks of additional births, and it allows couples and indeed single people who wouldn't otherwise be able to produce a child naturally to have children. Lots of social issues to think about!

  • $\begingroup$ "Probably not a whole lot"? What about the development of their brains and relationships? $\endgroup$
    – Raleon
    Aug 13, 2019 at 17:06

Physically, the child might probably be born looking like a regular three--months old baby.

Development of children does not stop after they are born. For example, the cranium of a newborn is soft at the top. The top of the cranium usually stops hardening at around 18 months of age for most babies.

Prolonging the time in a womb would mean development would continue in the machine.

I don't know about psychological effects, though. The contact between a child and the mother is critical for development. That's the basis for a lot of stuff that freudian psychanalysis tries to unpack. It may be that the vat children have a tendency towards some personality trait, but since we do not have humans being born out of vats nowadays anything is a guess. For an educated guess, you may do some research on whether premature children are predisposed towards some psychological trait.

As for how society would deal with it, it would probably follow the same stigmas as in vitro fertilisation, adoption and cloning.

The most orthodox religions would call it a mortal sin for a few years and, in an ironical moment of agreement with atheists, declare that such babies have no soul. That happened to Louise Brown, the first tedt tube baby, and some quick googling shows people are discussing whether she has a soul to this day.

Once the technology becomes commonplace, though, objections will cease. If you combine this with your previous questions on vat babies, there is potential for all kinds of dystopia. Think of the country of Gilead from the Handmaid's Tale if they had access to this technology.

Future doesn't have to be bleak, though. There are some good sci-i books in which almost everybody is a vat child, and the world is not (too) dystopic because of that.

In The Forever War, humanity chooses to go this way to control birth rates and avoid overpopulation.

In Dancing With Eternity, everyone is birthed in a vat and belongs to one company or another for a few years until they pay the costs of their birth, and then they are free. Due to the world veing a post-scarcity one, everybody lives in relative abundance, and they are all immortal and happy.

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    $\begingroup$ +1 and for good sci fi books don't forget Lois McMaster Bujold's Vorkosigan saga, where "natural" births are looked on as a risky weirdness by citizens of advanced societies. The babies are still decanted after 9 months though. $\endgroup$ Jul 27, 2019 at 3:27
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    $\begingroup$ Not just psychological effects, but immunological also. There's already research going on regarding how vaginal birth vs. C-section might affect rates of autoimmune disease. If that's even a possibility, then I would expect a three-month delay in allowing the child's immune system to start encountering environmental pathogens and developing the ability to counter them to be significant as well. $\endgroup$ Jul 27, 2019 at 7:54

Where to start...

Plasticity of the brain

Small children have periods in their life when they have a sensitivity to learn certain things. For example, its harder to a human over 5 years old to learn a new language perfectly, but it has been shown that a child adopted to another country during infancy will even in adulthood learn the language of their original country more easily. This sensitivity becomes more pronounced around the age of 40 weeks from gestation. When a newborn comes in contact with its environment, its brain blooms in activity. It looks in its mothers eyes, listens to its parent’s voices, suckles milk for the first time, sees a ball bounce of a surface, and every second 2 million synaptic connections are formed in its brain. It starts to move its limbs, realises it can control them, brings things to his mouth and starts on a path of becoming a fully functioning human. Pic1: Formation of synapses Pic2: Formation of synapses2

The most emotionally sensitive time is from 10 to 18 months. It is all a chain of events comprising of necessary steps to form a psycho-socially mature brain. This goes way beyond the timeline we are talking about, but as you can see from the first picture, in the beginning too many synapses form, and when the child grows, some of them are eliminated by apoptosis. This very important to form functional complexes on the brain cortex.

Psychological development of a baby

The psychological development of a human starts while it’s still in the womb. The mothers health, nutrition, stress level and other external things can affect the baby. In combination with genetic factors, they can start to form the future human’s character, temperament and self-control.

Since a baby can sense a lot during the third trimester, babies can recognise their mothers just hours after birth, if the mothers has looked and talked at the baby during these first hours. This means that the baby starts to bond even before birth. Newborns are capable and willing to communicate, any parent would know. They imitate, draw parents in with their crying and even prematurely born babies can have logical communication sequencies of mutual sound-making with their parents. These emotional connections gives the baby a ton of cognitive and social information that develop their brains, especially the limbic system that regulates emotions and mood. Early relationships have a huge impact on the development of a child’s social skills.

(Slightly off topic, but the saddest thing I have learnt about pediatrics is that when assessing why a child is falling behind in growth, after ruling out obvious reasons in nutrition and else you must also remember lack of love. Emotional deprivation can cause a child to stop growing. Luckily they catch up if they are moved to a fulfilling environment, but the cases I've heard of break my heart.)

Other points

Immunology: Immunoglobulins are passed on from mother to fetus through the placenta, and a newborn is protected from some pathogens due to this. Also going through the birth canal gives diversity to baby's bacterial flora compared to babies born by a caesarean section.

Breastfeeding: When possible, it is still the healthier choice for a baby. With advancement of technology a artificial human milk could be made, but it requires personalised antibodies (see previous point).

Prenatal development: auditory organs are formed at 26 weeks, and it is thought that language development starts in the womb. Artificial wombs should give outside stimuli to the developing baby even if they were decanted at 9 months.

Placental degradation: Placentas are partly formed by mother’s uteral lining and partly by the developing embryo. Forming of the embryos side of the placenta is a hugely important step in early development and cell placement, so I don’t know how you could eliminate that, even if the artificial womb formed the mother’s side of the plancenta. As others have answered, placental degradation becomes an issue around term, and even at just 42 weeks fetal distress becomes quite common, as the placenta’s function starts to slow down.

Nutrition: How much nutrition is a fully formed baby in suspension supposed to get? Should it grow at the same rate as it would if it was born or should it continue on fetal development? Without a functioning gastrointestinal system, the fetus is still relying on its placenta and umbilical cord arteries to get needed nutrition: glucose, free amino acids and some whole peptides, fatty acids, ions, vitamins. In the 9th month a fetus gains 7 grams of fat per day. I don't know for how long a umbilical cord stands that.

To recap:

Depraving babies from external stimuli for extra 3 mo might cause

  • lack of motor skills, maybe incapability to walk or at least poor hand eye coordination, balance, agility and comprehension of perception (?), since the window for most active sensorimotor development is around 9 months from gestation
  • slowing down of development of speaking and persisting linguistic understanding problems, due to not hearing speech
  • poor emotional control, inability to form mutual relationships, general lack of social skills due to lack of love :(

So yes, humans have evolved to give birth to immature babies, but the human baby-brains have evolved to use all the external stimuli starting from the early days to form the most complex network in the universe. You are proposing to disturb this intricate balance of too many synapses forming and later them being pruned, by removing three months worth of interaction with external stimuli in the most crucial period of synapses forming. Who the hell knows what kind of creatures you get, could they ever catch up?

Which came first, human sentience and intelligence or bipedal humans incapable of giving birth to independently functional progeny? I’d guess the latter.

Small sidenote, not something you asked, but relating to it and something you would want to consider in your story. How on earth would this technology come to be used? What kind of a researcher or medical professional in their right mind would start to suggest this? Maternal mortality in my developed country is one of the lowest in the world, 3/100 000, and there is a lot to be done to make it lower. Harvesting oocytes is never going to be risk-free either. Developing this artificial womb technology requires countless of human embryos. Which ethical board is going to give permission for that? What will the consensus reached on abortion be? These questions might seem like opinions, but having seen a glimpse of the medical research community, you need something really huge to threaten childbirth to justify this paradigm shift.

I apologise that my tone comes of as a bit aggressive at some points. :D I get worked up when people treat pregnancy and giving birth as some kind of a medical emergency instead of as the completely natural occurrence that it is. Maybe its the shock of witnessing childbirth, or maybe I have lately seen too many babies.

For reference I have mostly used books on pediatrics, pediatric psychiatry and neurology in my obscure maternal language.


I think that your vat-grown children might be significantly larger than natural born children, and might require some sort of pharmacopeia to keep them somnolent during their final days or weeks of gestation.

This is my reasoning, your vat-grown kids wouldn’t be constrained by the amount of nutrients their mother could supply. So they’d grow larger with more development.

The increased development would apply to their brains. They’d physically mature but lack sensory stimulation. The skull and brain would be larger at 12 months. But, would this mean they come out of the womb eager for exploring the world or would they be like an infant that hasn’t been touched for 3 mos — physically healthy but mental experience abandonment and isolation. If the exowombs provided the required intimacy and stimulation, then I think they’d be more advanced and pre-bonded with their mothers, would start learning at accelerated rates.


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