It takes about 38 weeks for a fertilised egg to develop into a full term baby.
The changes that occur over this short time are quite amazing.
This page describes some of the things that a fetus can do, and when they start (see here for an animation on fetal development).
All of the fetus’s senses will be stimulated naturally during the course of pregnancy, except for vision. The fetus has the ability to detect stimuli from as early as 8 weeks, in the case of touch. The environment of the fetus is not one of sensory deprivation.
The older fetus learns, while in the womb, to recognize certain sounds or tastes, and this prepares them for life after birth.
Note: Pregnancy is usually measured from the date of the beginning of the last period, and the egg is fertilised about 2 weeks after that. So although pregnancy is said to last for 40 weeks gestation, for the first 2 weeks of the 40 weeks of pregnancy there is nothing there.
Ultrasound technology enables us to clearly observe the fetus in the womb
Pregnant women usually first feel their baby move between 16-20 weeks gestation
The first movements are seen on ultrasound at 8 weeks gestation
The fetus can suck his/her thumb from 20 weeks
Common patterns of behaviour seen in adults are also seen in the fetus – e.g. handedness. Fetuses that suck their right thumb rather than their left thumb are likely to be right handed children.
Fetal movements increase and become more complex as the pregnancy progresses.
It is important for the fetus to practice all the movements that will be needed at birth for two reasons:
- Firstly it helps the brain and nervous system to develop well
- Secondly it allows the joints, bones and muscles to form correctly
The fetus does not actually breathe in the womb. The mother breathes for the fetus, and essential oxygen is passed to the fetus through the umbilical cord.
The fetus does make breathing-like movements though. These begin at 9 weeks of pregnancy and allow the fetus to practice this breathing movement.
This means that when the baby is born, he/she will be able to breathe straight away.
The fetus begins to move his/her eyes during the 14th week of pregnancy.
Complex movements, similar to our eye movements are present by the 24th week.
In the last third of pregnancy, rapid eye movements have been seen in the fetus. In adults, these occur when we are dreaming. Perhaps the fetus is dreaming too.
The fetus begins to respond to sounds at about 20 weeks into the pregnancy. To begin with the fetus only hears low noises, but as development continues he/she starts to hear higher pitched noises too.
Louder sounds can make the fetus startle and move about..
The older fetus is able to discriminate between different voices, languages, and even individual speech sounds, e.g. “BABI” and “BIBA”.
A newborn can recognise music that he or she heard in the womb.
Urinating, Drinking and Tasting
The fetus starts to empty his/her bladder during the 10th week of pregnancy. Urine is passed straight into the amniotic fluid, the protective fluid surrounding the fetus in the womb.
About five weeks later, the fetus starts to drink this same fluid.
So, while in the womb, the fetus is exposed to different tastes through the amniotic fluid.
The fetus likes certain tastes more than others, and will drink more amniotic fluid if it tastes sweet.
Becoming conscious/Feeling pain.
People often wonder when the fetus starts to be aware of itself or of signals coming in from the outside world.
When does he or she start to hear sounds or feel pain? We know with each other when someone feels pain because we can ask them and they can tell us. We cannot do this with the fetus, so we have to study when the brain develops enough to make this possible, and make an informed guess.
It is not enough just to study physical responses. For example, if you touch the foot of a fetus at 12 weeks, he/she will move away, but it is extremely unlikely that the fetus is feeling anything. This is just a reflex response like a knee jerk.
At this stage there is no connection between the nervous system in the body and the higher levels of the brain, which we think are necessary for conscious experience.
These connections between brain and body, necessary for feeling pain or hearing sounds, do not begin to start until about 17 weeks at the earliest, and are in general well formed and functional by about 26 weeks.
From 26 weeks onwards it does seem likely that the fetus can hear sounds and feel pain too. From about 20 weeks they may hear or feel something but it is hard to be sure.
Prenatal stress- fetal responses
The older fetus can sense what the mother is feeling. If the mother feels stressed or anxious playing a computer game, scientists have shown that the fetal heart rate goes up while she is playing it (see Monk and colleagues, 2000 or click here for more information).
Try our Stroop game to see this .