Smiles, laughter, giggles — as soon as the baby’s face lights up into a guileless smile, even the grumpiest passer-by melts and has to smile. Smiles are the reward for parents for all those sleepless nights and the manifestation of the connection which we yearn for from the first day of childbirth.
A smile tells us that everything is fine.
A smile makes us laugh back.
The smile makes us feel good.
When can a baby really start laughing? And why are they smiling?
What happens in the brain of a child and an adult when they laugh?
Does it have any effect on the development of the baby in the uterus and on the newborn, whether his mother often laughs or is depressed?
How can robotics help us to understand the effects smiles have on us?
Right after the delivery we take our babies and pack them into a cloth that holds their hands and legs close to their bodies, to let them feel hugged and safe. And so we tend to forget that they can already move, that back there in the womb, they were moving, touching, listening, observing. We greet every move of their hands and legs with huge applause. We observe how they start pseudorandomly move their hands around, kicking legs when they want to reach a toy as they are exploring options of their bodies. Like every mum, also I can spend many hours just watching how is the little baby exploring the world around. Slowly, as they touch by their hands and legs surrounding objects or themselves, they start to move more and more intentionally, and we focus on every step of their development with incredible attention. All this seems to be a continuous development with the starting point at delivery. We tend to forget about their first kicks in our belly, by which they were letting us know that they are already there, about those long nine months which they spent exploring the womb. How it was in there? How often they move, how important is their motor development inside the belly for their future motoric development at all?
Compared to other infrahuman primates (this means chimpanzees, apes, and others) human babies have delayed development [1, 2]. This means that for many weeks after the birth, the baby actually does not change much its behavior compared to what it was doing inside the womb. It is still not able to care for itself and needs long term support from the mother. It seems that there is a central movement pattern generator  in the brain, which creates various movements (either general movements of the whole body or isolated movements of the individual limbs) and this same pattern generator is serving the body both before and after birth . This gives us an amazing option to see, how was our precious bundle behaving inside our belly – which movements it used to do, how it sometimes accidentally touched its head by its hand, how it was sucking the amniotic water, how it was breathing, yawning, swallowing, kicking,… It takes up to 3 months after birth when these mainly random predefined motor patterns change to more intentional goal-directed movements, that are guided by the sensory system (which was also not fully developed in the first weeks after the delivery so the baby had to wait a bit longer to be able to make use of it) – and the baby can finally reach for a toy by hand or rotate in its direction…
Development of the motoric system
The motoric system is one of the first systems in the fetus’s body which starts to develop. It was shown that it is crucial for brain development that the motoric action provides an appropriate change in the sensorial world (e.g. we can feel that we touched something or we can see that something moved, etc.) (see e.g. Held and Hein  who performed a classic experiment with kittens). Thanks to modern ultrasound devices we can observe gradual changes in human fetus development in detail. First longitudinal studies were performed in the 1980s by Prechtl  and uncovered till that point many unknown phenomena about that secret world “inside”. From the studies of the motor patterns, we can nowadays observe also the brain connectivity of the fetus and see for example that good connectivity of some regions (prefrontal cortex, motoric network, supply motor regions, and temporal lobes) in the fetus brain is very important for later post-term motor development of the kids (Thomason, 2018). In this study, they found out that the connectivity also differs between female and male fetuses and discusses that this might be related to the later sex differences between infants. There are studies that show that female infants are better in fine motor skill development, while males in gross motor  or those female infants show more coordinated arm movements .
When do individual movements start?
As soon as in 8 weeks of pregnancy the fetus starts to move sideward its head . These first body movements are followed by generalized movements of the whole body in 9-10 weeks – the whole body is either moving slowly in a sequence (general movements) or all limbs, trunk, and neck are moved by quick phasic movements (startles) . It takes another week or two when we can (between 10-11 weeks) observe isolated local movements of one arm or leg. Isolated movements of some parts of the body are way more difficult to produce than whole-body movements both for the fetus as for the newborn. Teaching individual brain regions of the motor cortex to specialize for moving individual body parts will be under development for many years so it is no wonder that it is easier to generate in the fetus brain activity responsible for the whole-body movement. Just imagine when someone asks you to move one of your toes on your feet. Can you manage?
In the 10 weeks of pregnancy come hiccups. These movements are caused by repetitive short contractions of the diaphragm, which might last for several minutes and as you well know, they can be pretty annoying. Sometimes they might be so strong that they move the whole fetus in the womb.
If you wonder when the baby can already move its head to sign “no” or “yes” to your question by moving head back and forth or rotating it from side to side, it is actually as soon as in 11 weeks of pregnancy. At that time, the head becomes mobile and can move forward, backward, and rotate. It means that now we have to just find the way how to let the baby know that it can use it for communication with us and by observing the womb via ultrasonic devices, we can see if it likes or dislikes what we do 😊. What is great is, that this general pattern generator for limbs and head movements might create at this point accidental hand-eye contacts. These are totally not intentional, but still, provide important information for the fetus. These are the first self-contacts that enable later self-awareness of the baby and a better understanding of its own body. Same as we tried in our research where the robot was trying to touch itself to find out the length of its arms and torso as well as the position of its eyes (cameras) (Stepanova et al. , https://www.youtube.com/watch?v=zP3c7Eq8yVk&feature=emb_logo ).
In 11-12 weeks we can observe periodical breathing of the fetus and in 12 weeks we see stretches and yawns. It might impress you to observe your newborn yawning as it seems so mature. The fact is, that these movements which appear as soon as in 12 weeks of pregnancy will keep the same form and pattern for the whole life. Cool, right?
Sucking. You might be impressed by the newborn sucking reflex and then the strength of the sucking itself (at least some of the kids, some others need a lot of stimulation and their sucking is very weak). How quickly it finds the place to suck and how much it hurts when the baby actually sucks accidentally in the wrong place. No wonder, it has good training also for a few months before it comes to the world. After 12 weeks of pregnancy, the baby starts to drink the amniotic fluid, that is connected to first sucking and swallowing movements. As the sucking might happen in the womb all the time, after delivery, the baby will have to learn to connect this sucking behavior to feeding occasion – yet some of the kids would love to continue in the “sucking all the time” behavior 😊. Sucking reflex itself (meaning that the baby starts sucking as it gets nipple or something else to the mouth) develops around 32 weeks of pregnancy. (https://www.healthline.com/health/parenting/sucking-reflex#test).
At around 20 weeks, the baby starts to prepare for the outside world and first slow eye movements (20 weeks) followed by rapid eye movements (22 weeks) develop. 
As the fetus is growing and space is getting restricted, most arm movements end up not far from the face, and the amount of hand-face contact increases . The first movements are mainly unintentional, later there are also more and more non-reflexive responses to sensorial inputs – like to sounds, light (response to disturbances  or movements towards the source  (see also my earlier blog post about the language development), response to the maternal touch of the abdomen by an increase of arm, head and mouth movements  as well as changes in fetal heart rate. But still, most of the movements are only ‘‘motor babbling’’ – the spontaneous activity of the fetus.
By about week 21, the fetus begins to develop a regular schedule of movement  The startle reflex is present in half of all fetuses by week 24 and in all fetuses by week 28.
After the birth comes with sensory inputs also new options and new movements. The baby must deal with the gravity, it has to learn how to deal with the lung ventilation and so we can observe sneezing and coughing and so on.
The motor cortex of the fetus
It is believed  that the fetus is creating connections between motoneurons and muscles via these spontaneous movements when via general and isolated movements it receives various types of stimulations. In this way, specialized areas in the brain that are created to operate given body parts might be created. When individual body parts touches another body part or the outside world as well as when an outside stimulus triggers some sensation, all of these contributes in the creation of new neural connections and enable the fetus later to repeat any movement. You can see research about creating these somatosensorial maps in the brain of the humanoid robot (https://www.youtube.com/watch?v=ONiKEtIJc3Q&feature=emb_logo , Hoffmann ).
How often do babies change their position in the womb? And should you be worried if they do not kick enough?
I guess that every mother goes at some point through
that scary moment. Sitting on the sofa and thinking that the baby did not move
for too long. Starting to worry, counting seconds, getting scared if everything
is ok with the baby. Should I call a doctor? Should I worry? What is wrong with
this baby? Or when you come to the monitor before delivery and you everybody
around gets “a nice” monitor immediately, only you are the one staying there
longer, breathing deeply, sisters changing your position that the baby finally
moves…It is easy to get stressed.
Up to 16 weeks of pregnancy the frequency of movements gradually increases and around 20 weeks, calm periods (without any type of movements like general or isolated movement, hiccups, mouth movements, etc.) are very short (maximum 13 minutes, de Vries et al., 1985). One of the cool things about all those types of movements mentioned above is that our baby can change its position in utero. What is interesting, that this change in position happens way more frequently in the first half of the pregnancy (up to 25 changes per hour) than in the second half. So, when we can finally feel the first baby kicks (at about 20 weeks of the pregnancy), changes in position are way rarer . It is not that surprising if you consider that the baby does not have in the womb that much space anymore. It is believed, that this decrease in frequency is also connected to the emergence of inhibitory cortical influences . Second or third children may have more stretching room in the womb than first babies because a woman’s uterus is bigger and the umbilical cord longer after her first pregnancy. These children usually get more motor experience in utero and tend to be more active infants . Keep in mind that there are huge differences in movements and their strength. There are studies, which found out that boys might be kicking more than girls  with higher average movements at 20, 34, and 37 weeks. Anyway, the study was done only on 37 babies, which is really not a relevant sample (https://www.livescience.com/62928-why-babies-kick.html ). When we go for a monitor, you can see many mothers discussing if they should eat or not before it to make the baby move. What was found out is, that most of the movements of the fetus are not connected to the amount of glucose in the mother’s blood (it does not matter if she is after or before meal)? The only exception is breathing movements of the fetus which are easier observable after the meal .
So you do not have to be worried if your baby kicking patterns are changing if you feel its kicks some weeks later or earlier if sometimes it is kicking more and sometimes less, especially if you are distracted by your own activity. Anyway, by week 29, you should be feeling your baby moves well. On average, you should feel some type of their movements (kicking, rolling, stretching, even light movements count) at least 10 times within 2 hours . If you do not get these 10 kicks within 2 hours while being in a calm environment resting, you should change position, wait an hour or two, calm down and try to count once again. If you do not count a reasonable amount of movements even then, then it is a proper time to call your pediatrician, to make sure that everything is ok.
There is much more to tell about the motor development of the baby in the womb, especially about its brain development, but let’s continue some other time. There are still many secrets even when we have nowadays very good tools to look inside the womb. What we know for sure is that the movements of the baby in the womb (and all the sensorial inputs it gets thanks to them) are very important for its future development.
 Hadders-Algra, Mijna. “Early human motor development: From variation to the ability to vary and adapt.” Neuroscience & Biobehavioral Reviews 90 (2018): 411-427.
 Einspieler, Christa, Peter B. Marschik, and Heinz FR Prechtl. “Human motor behavior: Prenatal origin and early postnatal development.” Zeitschrift für Psychologie/Journal of Psychology 216.3 (2008): 147.
 PRECHTL, HF R. “Continuity and change in early neural development.” Clinics in developmental medicine 94 (1984): 1-15.
 Held, Richard, and Alan Hein. “Movement-produced stimulation in the development of visually guided behavior.” Journal of comparative and physiological psychology 56.5 (1963): 872.
 Prechtl, Heinz F., ed. Continuity of neural functions from prenatal to postnatal life. No. 94. Cambridge University Press, 1991.
 Touwen, Bert CL. Neurological development in infancy. London: Heinemann, 1976.
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 Lüchinger, Annemarie B., et al. “Fetal onset of general movements.” Pediatric research 63.2 (2008): 191-195.
 De Vries, Johanna IP, G. H. A. Visser, and Heinz FR Prechtl. “The emergence of fetal behaviour. II. Quantitative aspects.” Early human development 12.2 (1985): 99-120.
 Stepanova, Karla, Tomas Pajdla, and Matej Hoffmann. “Robot Self-Calibration Using Multiple Kinematic Chains—A Simulation Study on the iCub Humanoid Robot.” IEEE Robotics and Automation Letters 4.2 (2019): 1900-1907.
 Birnholz, Jason C. “The development of human fetal eye movement patterns.” Science 213.4508 (1981): 679-681.
 Fagard, Jaqueline, et al. “Fetal origin of sensorimotor behavior.” Frontiers in neurorobotics 12 (2018): 23.
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 Marx, Viola, and Emese Nagy. “Fetal behavioural responses to maternal voice and touch.” PloS one 10.6 (2015): e0129118.
 Vaughan, Christopher. How Life Begins. Dell Publishing Company, 1997.
 Hoffmann, Matej, et al. “Robotic homunculus: Learning of artificial skin representation in a humanoid robot motivated by primary somatosensory cortex.” IEEE Transactions on Cognitive and Developmental Systems 10.2 (2017): 163-176.
 Almli, C. Robert, Robert H. Ball, and Mark E. Wheeler. “Human fetal and neonatal movement patterns: Gender differences and fetal‐to‐neonatal continuity.” Developmental Psychobiology: The Journal of the International Society for Developmental Psychobiology 38.4 (2001): 252-273.
Language development is a topic that fascinates me for years and
it all started by observing my oldest daughter slowly responding and
developing her linguistic skills by interacting with the outside world.
Making funny but understandable errors, learning by trial and
error…Now when there is a small baby growing in my belly, which
response to touches and voices, I wonder how much it actually hears and
how much what it hears affects its future development…
of the people and research focuses on the brain of the newborn and the
language acquisition after the birth, but brain areas corresponding to
the language development appear in the brain already during the 30th
week of pregnancy, and as soon as from the 18th week of pregnancy, it
can ‘hear’ sounds of your body such as your heartbeat and since the 27th
week auditory learning becomes possible…There are studies that show
that a fetus in the womb reacts to the mother’s voice, to the music,
etc. There are also studies that show that when the baby is exposed to
one language during pregnancy and adopted at birth, it can afterward
still produce mother language sounds or distinguish some words from that
language. All these findings are impressive and bring up an interesting
question – how is the prenatal exposure to sounds and languages
affecting the later development of the language for the baby? Can we
improve kids’ linguistic or musical skills by prenatal exposure to
foreign languages, by talking to them or playing music to them? Or is
how much we talk to the kid affecting our bonding and connection to the
baby? Maybe we cannot answer these questions or not all of them, but we
can see a bit more, what is happening in the womb, we can explore the
life in the darkness and see how the small brain is a step by step
developing and responding to the outer world…
Neurophysiology of the fetus
First, let’s see, what happens with
the baby brain which enables it to hear and recognize the language, all
of which later leads to the fact that newborns might be soothed by
familiar sounds like an adult heartbeat or that they prefer mother’s
language to other languages…. The onset of hearing in humans is around 27 weeks of gestational age , but already since 18th or 19th week, the baby can respond to sounds of the body such as heartbeat or stomach rumbling 
as the human cochlea starts to be slowly functioning . That is the
time when external auditory inputs start to have an effect on the
reorganization of the auditory cortex . To test the onset of hearing,
 performed an experiment, where they exposed the fetus to pure auditory stimuli of different frequencies (100, 250, 500, 1000, and 3000 Hz) –
from 19 to 35 weeks of gestational age (GA). Measuring the responses by
loudspeaker on maternal abdomen and by ultrasound, they observed first
responses for 500 Hz at 19 weeks of GA, then responses to lower
frequencies appeared (At 27 weeks, 96% fetuses were responding to 250
and 500 Hz) and the latest ones were responses to higher frequencies
(responses to 1000 and 3000 Hz haven’t been observed till 33 and 35
weeks, respectively). As the baby brain matures, a big decrease (20-30 dB) in the intensity level required to elicit a response was
observed. This corresponds to the neurophysiological maturation of the
inner ear, which seems to be matured at the end of the 8th month when
all relevant neuronal synapses take their place .
In the 30th week, brain areas corresponding to language development are
developing ([5, 6]). As you maybe know, there is observed a left
hemisphere dominance for language processing, which seems to be
genetically given and we can observe asymmetric development of the brain already before birth.
For example, the temporal plane layer in the left hemisphere is larger
than in the right one. We can also observe that the left hemisphere has
different sensitiveness for speech already from birth (response was
measured by electrical activity – event-related potentials, Mehler).
Interestingly, the development of cortical regions that are connected to
language is slower in the left hemisphere than in the right one (e.g.,
right temporal plane develops at the 30th week of GA, but left one 7-10
days later) ([7, 5]). The fact that brain regions for language
development are distinct already at birth might be a partial
verification for Chomsky  hypothesis, that there exists a universal
innate grammar, which we just fill in with vocabulary and rules.
This above-mentioned development leads to the fact that after 32 weeks of gestation age, the baby may start recognize vowel sounds
from your language , which further leads to the findings which we
will mention later, that the newborn prefers the native language to
other languages .
Sound and music in the womb – is the baby partying there?
we measure what the baby actually hears? It is easy. You can just place
a microphone or hydrophone inside the vagina close to the baby’s head
You will hear a lot of background noise, body noise and mainly low frequencies around 500-700 Hz, all of which are highly attenuated
[10, 11, 12]. Nevertheless, mother voice and external speech will still
be clearly emerging above the background noise with well preserved
prosodic characteristics. [11, 12] found out that even some
phonemes/words are still recognizable (up to 30%). All these speech
connected sounds are quite silent as they are attenuated significantly.
Although you can hear all (close by) external speech, you will get
during your life in the womb most familiar with the mother’s voice,
because there is significantly better transmission of maternal voice
than of external voices – Querleu found out that there is 20dB attenuation of external voices and only 8 dB of mother voices
. How can this be explained? It seems that there are 2 pathways
transmitting the voice – one is the same for both maternal and external
speech, but the mother’s voice is transmitted also through body tissues
and bones which enables kids to get more used to this voice.
This is closely connected to the findings on the newborns, that mother’s voice has calming effects for < 2-week old kids and is more attractive for the newborn than other female voices. On the contrary, newborns do not show any preference for the voice of the father compared to other male’s voices,
even after 4-10 hours of exposure to the father’s voice after
delivery. [10a] Spence  went even further and found out that infants
prefer the maternal low-pass filtered voice, but not the maternal
What is another interesting finding is
that external auditory stimuli in general increases motor responses
(both long term and startle responses) as well as heart rate responses
, but the mother speech can decrease fetal heart rate – the most when the speech is in low frequencies and around 70dB. The responses of the fetus were
measured for tones, vibratory frequency noises, or EAL stimulations
during quiet and active sleep and during active and quiet wakefulness of
the baby – it has been found that although to tones the baby starts to
respond at 27-28th week of GA, to EAL stimuli motor responses appear
already in the 24th week . Bigger responses can be observed during
wakefulness than during sleep. Unborn babies might even start to cry if exposed to a sudden loud noise.
And how is it with the music? Feijoo  measured kids at delivery and 4-5 days old and found out that kids were soothed by the music which their mother listened regularly during last 3 months of the pregnancy way more than any other music.
Postnatal effects of prenatal stimuli
So you can see that it has
been found out, that familiar sounds might soothe crying newborn ,
including adult heartbeat, mother’s voice[13, 10], music , or soap
opera theme .
Question is, how can we find out what a newborn actually prefers? There is an experiment called the non-nutritive sucking behavior of
the newborn which is supposed to measure babies’ responses to
individual stimuli. What should this mean? It is easy, this technical
term hides an easy thing – behavior while sucking on a pacifier.
So basically we measure how much the baby is sucking, what are the
pauses between sucking and frequency of sucking. So easy :).
this method, it has been found that newborn babies exposed to the adult
heartbeat (72 beats/s) were sleeping earlier and gained weight quicker
. Also, intrauterine background noise had a short term pacifying
effect ([10a], Murooka ). Familiar stimuli were also preferred by a
child in selection tasks.
Back to mother’s
voice…DeCasper  found out that 2-3 days old babies preferred a
story that mother read 6 weeks prior to pregnancy to the one they never
heard. And have you ever heard about fetal ‘soap’ addiction? It
was described by Hepper in 1988 , . What they found out? That
there were mothers who regularly watched a soap opera ‘Neighbors’ during
the last weeks of pregnancy (some even twice a day). Maybe you can
already guess what they observed for these babies after delivery. A
crying baby who was ‘listening’ to the soap opera already in the womb,
is more likely to stop crying when the program begins than the baby of a
mother who was not watching it in her pregnancy.
So far I was mainly speaking about voice and sounds, but what about the actual languages? Moon [9a], measured 40 infants about 30 hours old in the nursery using the test for sucking behavior when listening to vowels from native and unfamiliar language.
They found out that babies were sucking longer for the foreign language
than for the native tongue (independent on time since birth, 7-75h),
which indicates that they can differentiate between these two languages
and it seems that the ambient language to which fetuses are exposed in
the womb affects their perception of the native language at phonetic
level. In another study, Moon et al.  measured 2 day old kids of
French and Russian mothers while the same bilingual woman was talking to
them. These kids again preferred the mother’s tongue to the unfamiliar
one and the same behavior was observed also for low-pass filtered
versions, which kept only the prosodic cues of the languages. On top
when they measured kids from families speaking neither French nor
Russian, they were not able to discriminate between these 2 languages.
Maybe you might be a bit skeptical about this
sucking behavior test…Then there is another study conducted by May et
al. , who measured a neural activity of the brain using NIRS (near-infrared
spectroscopy) study on 20 monolingual English 0-3 days old neonates.
She let them be exposed to low-pass filtered sentences of forward
English (familiar language), forward Tagalog (unfamiliar language), and
backward English and Tagalog (non-language) and measured neural
activation by NIRS. They found out bilateral (in both hemispheres)
activation connected to the familiarity of the language and observed
different activation for Tagalog (unfamiliar language). This indicates
that exposure to the language in uterus influences the brain responses of the baby to the native language after birth.
So it actually seems that babies in the womb really listen to us as soon as their hearing enables them so,
although what comes to them is highly attenuated and filtered for high
frequencies. After several months of this auditory experience, they
become attracted to the familiar sounds and patterns of the native language(s).
But it is possible that they actually learn even more from their
prenatal experience as they might become familiar with the prosody of
the languages heard in utero (‘prenatal prosodic bootstrapping’), which
might be crucial for later language acquisition . To conclude, we
can see that long-term premature exposure to auditory (or other sensory
stimuli) in utero might lead to both prenatal and postnatal responses to
And one last thing to mention, the
auditory and language system as a whole continues, of course, to develop
also after a birth – e.g., hearing develops for another 5-6 months
after birth and language areas keep developing for years, so it needs
continuous stimulation through speech, music, and other sounds,
otherwise we might miss the important times (so-called sensible periods)
for its development which might lead to its underdevelopment, as
observed for linguistically or socially deprived ‘wild kids’…but that
is a topic for some other time…
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 Pujol, Rémy, and Adini Uziel. “Auditory development: peripheral aspects.” Handbook of human growth and developmental biology 1.Part B (1988): 109-130.
 Chang, Edward F., and Michael M. Merzenich. “Environmental noise retards auditory cortical development.” science 300.5618 (2003): 498-502.
 Gazzaniga, Michael S. The new cognitive neurosciences. MIT press, 2000.
 Department of Biochemistry and Molecular Biophysics Thomas Jessell, Steven Siegelbaum, and A. J. Hudspeth. Principles of neural science. Eds. Eric R. Kandel, James H. Schwartz, and Thomas M. Jessell. Vol. 4. New York: McGraw-hill, 2000.
 Chi, Je G., Elizabeth C. Dooling, and Floyd H. Gilles. “Gyral development of the human brain.” Annals of Neurology: Official Journal of the American Neurological Association and the Child Neurology Society 1.1 (1977): 86-93.
 Chomsky, Noam. “Recent contributions to the theory of innate ideas.” A Portrait of Twenty-five Years. Springer, Dordrecht, 1967. 31-40.
 Querleu, Denis, et al. “Fetal hearing.” European Journal of Obstetrics & Gynecology and Reproductive Biology 28.3 (1988): 191-212.  Busnel, Marie-Claire, C. Granier‐Deferre, and J. P. Lecanuet. “Fetal audition.” Annals of the New York Academy of Sciences 662.1 (1992): 118-134.
During all my pregnancies I always wondered how are fetus sleep/non-sleep periods related to my own sleep. And how my own sleep is related to the baby brain development and affecting the kid in general. Now it is my third pregnancy. I have way more work as a researcher, two kids already occupying me during the day and waking me to prepare them breakfast in the morning (somehow always too early) and there are too many nights when I just get too little sleep. It seems as the proper time to finally explore the effects of my behavior in detail and try to understand this hidden secret which is happening somewhere inside my growing belly. Is it anyhow harmful for the kid when I do not sleep enough as it still can happily sleep its 90% of time, or is my tiredness affecting the kid’s development by different substances floating to the womb or via changes in hormone levels in my body? Does the kid’s brain develops differently during my sleep and during my awakened periods? Another interesting thing for me was that the small baby in my womb seemed to move more when I was resting and its movements seemed almost unnoticeable when I was hiking or being anyhow active. When and how it actually sleeps and how it might feel?
How sleep deprivation affects adults is quite known and there are many resources on this topic. It has been shown that prolonged sleep restriction (less than 6 hours per night) or prolonged extended sleep duration (more than 9 hours of sleep per night) are associated with increased mortality . But how it affects the fetus, is way more hidden secret. So let’s dwell to this fascinating topic…
Sometimes we think about a fetus and newborn as two totally separate beings. Or at least for me, the kid which is still in my womb is totally different from the newborn which will come out and start being hearable and touchable. There are those moments, which make the unborn baby more present for me – like the ultrasonic or when you feel the baby kicking. Anyway, at least for me, the baby in the womb is still very silent creature, which is difficult to understand. Sometimes I have a feeling that it is just the belly, sickness, tiredness and so on, which I have to deal with, forgetting, that inside is a new small human being growing. The current neuroscience research reveals more and more about what is happening inside the womb during the pregnancy. And it is indeed fascinating story. As measuring the fetus brain activity in the womb is very challenging (there exist fetus fMRI , or fetal EEG measurements from scalp of a baby during labor or from mother abdomen , but these measurements are very prone to noise and the interpretation of the data is very challenging), we are mainly restricted to external explorations. It seems that all the way long from the week first till the delivery, there is a continuous process of cognitive development of the kid – not only preparing the physical body, body and brain cells, not only developing digestion, training breathing and motorics, but also improving voice recognition, language development, learning and memory, other cognitive functions, and maybe even dreaming. This process continuously follows to a newborn stage. There is no strict border between a fetus and a newborn.
And same it is with the sleep. The baby in the womb spends almost all the time asleep. As it approaches 32 weeks, it still sleeps 90-95% of the day. Every week the amount of sleep is a bit reduced and at delivery time, they sleep around 85-90% of the day, which is the same time, as the newborn will sleep when coming out of the womb. It might be, that during sleep the fetus is even dreaming as it spends some time in REM phase of the sleep with eyes moving quickly back and forth. “Around the seventh month of a fetus’ development, the first rapid eye movements are seen. The brain of the developing embryo appears to cycle every 20 to 40 minutes between REM sleep, in which brain activity rivals that of consciousness, and non-REM sleep, in which the brain rests.” Swab  explored the fetus of a sheep and came to the conclusion that “Sleep does not suddenly evolve from a resting brain. Sleep and sleep state changes are active regulated processes,” How are these different stages of the brain activity important for the brain development is still a research question. “Cyclic changes in the activity of neurons, for instance, may stimulate the other nerve cells to find and connect with each other to set up complex networks in the brain.”
You can see visualisation of fetus sleep cycles by 26th to 30th week of pregnancy on this video:
It is known that sleep and its individual stages are important for fetal and early neonatal brain development, including development of the neurosensory and motor systems, for learning and memory in the fetus and neonate and for preserving the brain plasticity.That is why the brain of an infant or child is more active during some stages of sleep than during wakefulness and awake activities.  The importance of sleep and sleep cycles for the fetus in utero and the preterm infant in intensive care unit is known for more than 40 years.  REM sleep deprivation in kids might result in disordered sensory system, disordered learning and memory, disordered or disrupted learning and memory creation, loss of cortical plasticity into adult life and also smaller adult brain size. The deprivation of Non REM sleep might result in decreased learning and memory consolidation from sensory experiences, less ability to learn in childhood and adult life and loss of brain plasticity into adult life. 
The main question for me is how my behavior is actually affecting the sleep of the fetus? It seems that when I am more active, the kid can more happily sleep and when I am resting, it starts to wake up. . In  Kintraia et.al explored the daily rhythmicity of 2500 fetuses using the electrotachogram and they found out that “daily rhythmicity of fetal electrocardiogram resembles that of the mother; however, the phase of the rhythm is opposite to that of the mother. “Active” (from 9 a.m. to 2 p.m. and from 7 p.m. to 4 a.m.) and “quiet” (from 4 a.m. to 9 a.m. and from 2 p.m. to 7 p.m.) periods of activity were identified.” A baby may be more active about an hour after the mother eats. This is because of the increase in sugar (glucose) in the mother’s blood. Fetal movement normally increases during the day with peak activity late at night.”
Anyway, there is evidence that the mother activity might directly affect the fetus behavior “ultrasounds have shown a fetus bouncing up and down when the mother laughs.”  Also mother movements and activity actually might make it more pleasant for the kid to sleep then when she is in a calm position. What is interesting is that the baby’s brain won’t produce melatonin till the age of 3 months to develop its own circadian clocks. So in the womb it relies on signals from your body clock as melatonin can cross the placenta and after birth, some amount of melatonin can still be passed to the baby through breastmilk. Until circadian clock develops, newborn sleep patterns will be fairly irregular.  It is also interesting to see the research of the fetus activity based on the mother sleep position. In  they explored 36 pregnant women and found out that when the mother slept on her back, the fetus was less active. As the fetal activity is one measure of its well-being, it is suggested for women to sleep on their side during the later pregnancy (after 28 weeks) to reduce the risk of stillbirth.
You maybe would like to predict the sleep pattern of the newborn and other infant behavior from the fetus movements. Unfortunately, based on the DiPietro study on 52 healthy fetuses, there is no evidence for such predictions [14, 15],
How mothers sleep deprivation affects the fetus?
It might not be only due to the fact that you have a lot to do in the evening why you cannot have a really long night of well-quality sleep. I have to say that in this sense I was quite lucky as I sleep typically quite well. Maybe due to the fact that I typically go to bed later than I should, I have no problems to fall asleep directly and if I do not drink a liter of water before sleep, I can survive without toilet sometimes even till the alarm or kids wake me up. So my main problem is to find enough hours for sleep. Many women however have other reasons for sleep deprivation – insomnia, restless legs syndrome, frequent nighttime urination, etc.[16, 17] My concern is now about my night papers deadlines, when I do not get enough sleep, what then happens to the baby?
“Sleep deprivation during pregnancy has been associated with longer labor, elevated perception of pain and discomfort during labor, higher cesarean rates, preterm labor, and higher levels of pro-inflammatory serum cytokines. Limited research has also indicated a possible relationship between sleep deprivation and preterm births and postpartum depressive mood.”  However the studies are typically done on poorly controlled studies and non-representative samples. Study on more than 1000 women showed that Women with severe snoring were at high risk for low birth weight, and fetal-growth-restricted neonates and women with sleep deprivation (≤5 hours sleep) were at high risk for preterm births, with the highest risk observed for medically indicated preterm births [19,20].
The most interesting topic for me is if the mother sleep deprivation might actually also affect emotional and cognitive development of the baby. One of the effects on the cognitive development of the newborn might be the fact that the sleep deprivation during pregnancy increases the risk of postpartum depression, which in consequence increases the risk that the mother-child bonding is not created properly which in consequence can affect the kids emotional and cognitive development. Corresponding to the more direct effects on the cognitive development of the child, it is very challenging to perform the real experiment on humans as it is not really ethical to sleep deprive women and create meaningful controlled studies.
At least, there have been done several interesting studies using rats. In  they sleep deprived pregnant rats and then investigated the offsprings and found impaired hippocampal-dependent spatial learning and memory, and increased depressive- and anxiety-like behaviors. In  they observed “increased brain derived neurotrophic factor (BDNF) in the hippocampus of fetuses of sleep deprived mother rats, which indicates that sleep restriction of mothers during the final week of gestation (last trimester of rats pregnancy) may affect neuronal growth factors in a fetal brain structure, in which active neurogenesis occurs during the deprivation period. However, no changes in the total reactive oxygen species (ROS) in the cortex, hippocampus, or cerebellum of the fetuses were detected.” In  they found out that sleep deprivation during late pregnancy can produce hyperactivity and increased risk-taking behavior in rat offspring.
 Sleep and mortality: a population-based 22-year follow-up study. Hublin C, Partinen M, Koskenvuo M, Kaprio J Sleep. 2007 Oct; 30(10):1245-53.
 The article “Nonlinear analysis and modeling of cortical activation and deactivation patterns in the immature fetal electrocorticogram,” by K. Schwab et al was published March 31, 2009. [Chaos 19, 015111 (2009)]. The article is available at https://aip.scitation.org/doi/10.1063/1.3100546. Journalists can obtain a copy of the article by emailing
 Peter R. Stone, Wendy Burgess, Jordan McIntyre, Alistair J. Gunn, Christopher A. Lear, Laura Bennet, Edwin A Mitchell, John M. D. Thompson. An investigation of fetal behavioural states during maternal sleep in healthy late gestation pregnancy: an observational study. The Journal of Physiology, 2017; DOI: 10.1113/JP275084