How does prenatal development work? - Chapter 2

How does prenatal development work?

Throughout history, many different ways to view prenatal development can be found. Aristotle rejected the idea of epigenesis, the emergence of new structures and functions during development.

For example, the Beng in West Africa believe that every baby is a reincarnation of an ancestor. The spirit of the ancestor, the wru, does not yet want earthly life and retains a double existence, traveling back and forth between the present and the wrugbe, the spirit world. If the child dies before the umbilical stump has dropped of, there is no funeral because it is assumed that the child is not yet a person and has returned to the spirit world.

What is conception?

Gametes are reproductive cells (ovum or sperm) that contain only half of the genetic material of all other cells in the body. Gametes are produced by meiosis, a special type of cell division where the egg cell and sperm cell receive only one member from each of the 23 chromosome pairs. An egg cell and a sperm cell together form a complete set of 23 chromosome pairs.

Conception is the joining of an egg cell from the mother and a sperm cell from the father. During the ejaculation, the sperm cells travel through the uterus to the egg for 6 to 7 hours. Only 200 of the 500 million sperm cells survive this journey. It is a process like in Darwin's theory: survival of the fittest. There can be several reasons why sperm cells does not make it to the egg cell. First, there may be problems with the sperm cells themselves, which is sometimes based on a genetic defect. It is also possible that sperm cells get entangled with each other during the trip. Finally, it is possible that the sperm cells go into the fallopian tube that does not harbor an egg. One sperm cell fertilizes the egg cell. A fertilized egg is called a zygote. By a chemical reaction, which occurs when a sperm cell reaches the egg cell, a layer is formed around the egg, so that other sperm cells can no longer reach or fertilize the egg cell. In the first two weeks, the fertilized cell is a zygote.

What processes of development take place?

From 3 to 8 weeks the fertilized egg is called an embryo, from the 9th week on it is called a fetus.

The development process of the fertilized egg cell consists of four processes:

1. Mitosis: cell division, starts 12 hours after fertilization.
2. Cell migration: the movement of new shaped cells away from their original location.
3. Cell differentiation: all embryonic stem cells can develop in any type of cell, these cells will specialize in structure and function.
4. Apoptosis: cell killing, for example, the membranes between fingers and toes are removed.

For a long time it has been thought that more male than female embryos were conceived. Male fetuses are more vulnerable to early abortion and often have a lower birth weight than females. Recent research shows that the chances of a male and female embryo are the same.

What does prenatal development look like?

The fourth day after conception, the cells organize themselves in a hollow ball with a number of cells (inner cell mass) on one side. This is the stage where identical twins originate because the inner cell mass splits by half, so they have the same genes. Fraternal twins, on the other hand, result when two eggs are released from the ovary into the fallopian tubes and are both fertilized.

The inner cell mass (also called embryoblast) is eventually formed into a fetus. In the second week after fertilization, the inner cell mass folds into three u-shaped layers. The first layer contains the nervous system, nails, teeth, inner ear, eyes, and the upper skin layer. The second layer contains muscles, bones, the circular system, inner layers of the skin, and internal organs. The third layer contains the digestive system, lungs, the urinary tract, and the glands. Then the neural tube is formed, which consists of the brain and the spinal cord. The cells that do not belong to the inner cell mass (the trofectoderm) form the placenta and the amniotic sac. The placenta transports materials through the blood stream between mother and fetus, protects the fetus from toxins, and produces progesterone and estrogen. The amniotic sac is a membrane that is filled with water that protects the fetus. The blood vessels that connect the placenta and the embryo are collected in the umbilical cord. The development of the fetus is a so-called 'cephalocaudale' development, where the parts of the body close to the head develop faster than parts of the body that are further away from the head.

How does a fetus behave?

The fetus starts to move after 5 to 6 weeks. The first movements are hiccups and swallowing. After twelve weeks almost all movements are present that are present after birth. From 10 weeks onward, the fetus starts to 'breathe'. There is not really air in the lungs, but the fetus moves the chest up and down to kind of exercise.

The visual experience of the fetus is minimal. However, it appears that during the last trimester, fetuses have a visual preference for faces that look straight at them over faces that are upside down. The fetus also experiences tactile stimulation through its own movements, which affects its own body parts and the uterine wall. The amniotic fluid has different flavors, the fetus can detect it and also has a preference for different flavors. The amniotic fluid can also bring smells of what the mother has eaten, these smells give the fetus the opportunity of olfactory experience. The fetus also hears everything, the heartbeat of the mother, her breathing, her swallowing, but also her voice. In the last trimester the fetus can record sounds from the environment.

How does the fetus learn?

In the last three months, the fetus learns from experiences. At that time the central nervous system has been developed far enough to support learning. Habituation is a simple form of learning in which a decrease in response is caused by repeated or permanent stimulation. Dishabituation arises when there is a perceptual change in the stimulus, so that the infant is interested again. These two forms of learning both occur in the womb and memories of it continue to exist after birth.

Phylogenetic continuity is the idea that, because of our common evolutionary history, people share many characteristics, behaviors and developmental processes with other animals, especially mammals. This assumption is the basis for animal research. Thanks to research on mice for example, we know that alcohol can cause a fetal alcohol spectrum disorder during pregnancy. It has also become clear that baby mice can smell the amniotic fluid on the nipples of their mothers, that is how they find the nipples.

What kind of negative events can take place during prenatal development?

It is possible that something goes wrong during pregnancy, such as a miscarriage. Genetic factors can also play a role in a pregnancy that does not go well.

Environmental factors play an important role during pregnancy. Teratogens are external substances that can damage the unborn baby during pregnancy. It may even be the case that these harmful substances kill the unborn baby. However, it is a question of timing, because when these toxic substances come into the picture during the so-called sensitive period, they can cause more damage than when these toxic substances are present outside the sensitive period. The sensitive period is a period in which the development of the baby is most susceptible to the effects of external factors. Different sensitive periods exist for different systems. For example, the sensory period for the development of the central nervous system is mainly between 3 and 5 weeks, after which it develops further. Whereas, the sensitive period for the development of the palate is between 7 and 8 weeks, and also develops further after. In addition to timing, the duration of exposure and quantity of toxic substances is also important for problems with the pregnancy. Most teratogens show a dose-response relationship. This is a relationship in which the effects of exposure to toxic substances increase with the degree of exposure. In other words: the more exposure to teratogens the fetus has, the more serious the effect on the fetus are. The effects may also depend on individual differences. These effects sometimes only become visible after years.

Depression during pregnancy can lead to disability of the child, such as social and cognitive problems. However, drugs to treat depression, especially SSRIs, can have adverse effects on the baby, such as a later diagnosis of autism. This makes it very difficult. Behavioral interventions have promising effects to treat perinatal depression.

The use of opioids for pain can seriously damage the fetus. Fetuses can have the neonatal abstinence syndrome (NAS), where a form of withdrawal symptoms is seen, the fetus has become addicted to the opioids.

Illegal drugs are dangerous for prenatal development because they affect the developing brain of the fetus. Marijuana is a drug that is often used and associated with problems with attention, learning and memory in later life.

Smoking also has negative effects on the fetus. The fetus gets less oxygen. The child is more likely to have problems at a later age such as lower IQ, hearing problems, ADHD and cancer.

The consumption of alcohol during pregnancy may result in fetal alcohol spectrum disorder (FASD), which may lead to the fetal alcohol syndrome (FAS) where the baby is characterized by facial malformations.

Pollution of the environment can also cause damage to the fetus. For example, the bodies and blood of most American women contain a mixture of toxic metals, synthetic hormones, plastic, pesticides and herbicides that may be teratogenic.

Maternal characteristics can also influence prenatal development, including age, nutritional status, health and stress levels.

Children with teen mothers of 15 years or younger are 3-4 times more likely to die in the first year of life than children of mothers between 23 and 29 years of age. If a mother does not get enough of certain vitamins or nutrients, it can have serious consequences. Some diseases also affect the fetus. For example, HIV can be transmitted to the child. The Zika virus is another well-known example, this virus leads to microcephaly in the child. If the mother displays high stress levels during pregnancy, the risk the child shows behavioral problems is higher. It is difficult to determine whether this is only due to the stress, as there are often several factors involved. However, yoga and meditation prove to be good for both the child and the mother.

The sudden infant death syndrome (SIDS) is the sudden, unexpected death of a child younger than 1 year without identifiable reason. One hypothesis is that there is an inadequate reflexive response to blocking of the breath. Recommended is to let babies sleep on their back and ensure a firm mattress without a pillow. Parents should not smoke either. Children who are breastfed and / or using a pacifier are less likely to have SIDS. In addition, it may be wise to let the child sleep in the same room.

How does the process of birth take place?

The muscles of the uterus start to contract at about 38 weeks of pregnancy. It is called labor pain. Mothers are often treated with medication during birth to cope with the pain, this doesn't affect the baby. However it can extend the duration of the delivery and more tools may be needed. During the birth the flexing/ squeezing does not hurt the baby, but the mother experiences the stretching as painful. Squeezing removes the uterine fluid in the baby's lungs. This allows the baby to breathe right after birth for the first time. This is what babies do by crying.

There are many differences in behavior around birth between cultures. All cultures are focused on the survival and health of the child during birth, and the social integration of it.

How does a newborn baby behave?

The state of arousal involves the level of mental alertness or consciousness, such as very deep sleep or intense activity. There are two newborn 'states' that are mainly interesting: sleeping and crying. Sleep consists of REM sleep and non-REM sleep. REM sleep involves an active sleep characterized by rapid eye movements behind the eyelids. In adults, it is associated with dreaming. Non-REM sleep involves a quiet and deep sleep characterized by slow brainwaves, quiet breathing, a quiet heartbeat and absence of motor activity and eye movements. The older a child becomes, the less sleep the child needs.

Babies cry for various reasons, illness, pain and hunger are a few examples. A much used tranquilization technique is swaddling, where the baby is tightly wrapped in a blanket or clothing. This ensures continuous tactile stimulation and warmth. Putting something sweet in the baby's mouth also has a calming effect. Research shows that it does not matter whether an immediate reaction is made to the crying of a child or that the crying is ignored, in both cases the child will cry less in the future. When an infant cries excessively and inconsolably, without any reason, it is called colic.

What negative events can take place at birth?

In most cases, babies are delivered healthy into the world. Sometimes this is not the case. The most serious case is the death of a born baby in the first year of life. This is called infant death. Due to improvements in health care, however, this has become less and less prevalent over recent years. Another negative consequence of birth can be a low birthweight. This low birth weight (LBW) is characterized by a weight of 2.5 kg or less. Reasons for low birth weight can be: a premature baby (pregnancy of 35 weeks or shorter instead of 38 weeks, also called premature), or the baby is born too small (small for gestational age). This can have consequences in the longer term, for example social problems or learning disabilities. To prevent these consequences, physical contact with the newborn baby is often avoided because of the risk of infections. However, the majority of babies with low birth weight survive, without showing problems later in the development. Today, there is more consensus on this topic in science, and healthcare is committed to interventions that maximize physical contact between parents and the baby. Often babies with low birth weight receive massage therapy.

Another negative influence after birth is poverty or a low SES (socio-economic status). This can lead to a less positive development of the baby. According to the multiple risk model, the baby has more problems with development if several risk factors are present at birth. However, if there are different risk factors, this does not mean that there is always a negative development. This is the developmental force. In other words: successful development despite the multitude of risks that affect the birth.