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There are several terms to describe the different stages of pregnancy. When an egg and sperm meet, a zygote is formed and it begins to divide to become an embryo. As pregnancy progresses, the embryo becomes a fetus. The fetal period of prenatal development marks important changes in the brain. This developmental period begins at week nine and continues until birth, when the fetus becomes a newborn baby.
Fetus – stages of development
When cell differentiation is mostly complete, the embryo enters the next stage and becomes known as a fetus. The fetal period begins on the ninth week and continues until birth. This stage is characterized by changes in the body and growth of the fetus. The early embryonic systems and structures are still developing. The neural tube (or the neural tube) develops into the brain and spinal cord, and neurons continue to form. Once the neurons are formed, they begin to migrate to their proper locations. Synapses, or connections between neurons, also begin to develop.
Between nine and twelve weeks of pregnancy, reflexes begin to develop. The fetus begins to make reflex movements with the arms and legs. In the third month of pregnancy, the sexual organs begin to differentiate. By the end of the month, all parts of the body will have formed. At this point, the fetus weighs about a kilogram. It will continue to grow in both weight and length, although most of the physical growth occurs in the later stages of pregnancy.
The end of the third month also marks the end of the first trimester of pregnancy. During the second trimester, which is the fourth to sixth months, the heartbeat becomes stronger and other body systems continue to develop. Toenails and toenails, hair and eyelashes are formed. Perhaps the most noticeable thing is that the fetus grows in size by about six times. With the second trimester, or more precisely around the twenty-eighth week, the brain begins to mature faster.
In the seven months to birth, the fetus develops, gains weight, and prepares for life outside the womb. The lungs begin to expand and contract, preparing the muscles to breathe.
Also check: Zygote, embryo and embryo – the development of a child in the early stages after conception
Fetus – development of blood circulation
The fetal circulatory system uses three fistulas to direct the blood that needs oxygenation. The purpose of fistulas is to bypass the lungs and liver. This is because these organs will not be fully functional until you give birth. The fistula bypassing the lungs is called the foramen oval (Latin. foramen ovale). It carries blood from the right atrium of the heart to the left atrium. The arterial duct (lat. ductus arteriosus) carries blood from the pulmonary artery to the aorta. Oxygen and nutrients from the mother’s blood are sent through the placenta to the fetus. The enriched blood flows through the umbilical cord to the liver and is divided into 3 branches. The blood then reaches the inferior vena cava. It is the main vein connected to the heart.
Most of this blood is sent through the venous duct (Latin. ductus venosus). It is also a fistula that allows highly oxygenated blood to flow through the liver into the inferior vena cava and then into the heart’s right atrium. A small amount of this blood goes directly to the liver to provide it with the oxygen and nutrients it needs. Waste products from the fetal blood are carried back through the placenta into the mother’s blood.
The heart of the fetus
When blood enters the right atrium, most of it flows through the foramen ovale to the left atrium. The blood then travels to the left ventricle and then to the aorta (the large artery coming out of the heart).
From the aorta, blood is sent to the heart muscle itself, and to the brain and arms. After circulation, the blood returns to the right atrium through the superior vena cava. Very little of this less oxygenated blood mixes with the oxygenated blood. Instead of coming back through the foramen ovale, it goes to the right ventricle.
This less oxygenated blood is pumped from the right ventricle into the pulmonary artery. A small amount of blood flows into the lungs. Most of this blood flows through the arterial duct to the descending aorta. This blood then enters the umbilical arteries and flows into the placenta. In the placenta, carbon dioxide and waste products are released into the mother’s circulatory system. Oxygen and nutrients from the mother’s blood are released into the blood of the fetus.
After birth, the umbilical cord is tightened and the baby no longer receives oxygen and nutrients from the mother. With the first breaths of life, the lungs begin to expand. As the lungs expand, the alveoli in the lungs are cleared of fluid. An increase in the child’s blood pressure and a significant decrease in pulmonary pressure reduce the need for blood to be transfused through the arterial duct. These changes help close the fistula. These changes raise the pressure in the heart’s left atrium. They also lower the pressure in the right atrium. The pressure change stimulates the closure of the foramen ovale.
Closure of the arterial duct, venous duct and foramen ovale completes the transition from fetal to neonatal circulation.
See also: The 10 most common diseases of the circulatory system
The fetus – development of the immune system
The cells that are formed in the embryo will become cells of the immune system over time. These early cells of the immune system, called hemopoietic stem cells, have proteins on their surface that allow scientists to identify them as precursors to immune cells. In early pregnancy, these cells divide very quickly, but as the fetus matures, their rate of multiplication slows down and more of them become specialized cell types. Preterm babies tend to have higher numbers of these non-specialized cells than term babies.
These cells travel through the blood to organs related to the immune system, such as the liver, spleen and thymus. By the second or third month of pregnancy, some of them become T cells. Although these T cells are active in the third or fourth month of pregnancy, the sterile environment of the uterus does not require the fetal immune system to fend off potential pathogens.
It is worth emphasizing at this point that in the case of pregnancy, we are dealing, in a way, with two immune systems in one organism. It is still unclear exactly why the mother’s immune system does not attack the foreign element in the fetus. It is believed that this may be due to the fact that the fetal immune system does not have to work in the womb, it can be safely suppressed, and because the cells of the fetus pass through the placenta and circulate in the mother’s body. These cells can be detected in the mother between weeks four and five of pregnancy and remain for years or even decades after giving birth. The presence of genetically distinct cells in an individual, such as fetal cells found in the mother, is called microchimerism. This exchange of cells from the fetus to the pregnant woman provides another possible explanation for why the mother’s immune system does not reject the growing fetus.
And while it is important for the fetus to grow in an environment where it is not rejected, it is not without consequences for the developing immune system. These consequences become important when the baby leaves the sterile conditions of the uterus and encounters a bacterial-rich vaginal environment and a non-sterile world. Immediately after birth, the baby’s immune system has to start working, what is more, the baby who was previously in the womb had no contact with any pathogens, so he must gain experience. The mother’s body turns out to be helpful in both of these matters.
First, the mother’s body produces antibodies that begin to cross the placenta in the thirteenth week of pregnancy, but most of them cross the placenta in late pregnancy, in the third trimester. The result is that preterm infants tend to have lower levels of circulating antibodies in the blood and are therefore more prone to infection than term infants. Placental-borne antibodies are mainly immunoglobulin G, and although they provide important protection, they can sometimes cause harm, for example, it is not uncommon that maternal antibodies against fetal red blood cell proteins can cause anemia and jaundice in the newborn.
Secondly, breast milk is also crucial to provide protection in the form of antibodies, immune cells such as macrophages and other immune factors such as cytokines. This is especially true for milk produced in the first days after birth, known as colostrum. Studies have shown that each milliliter of colostrum contains up to 3 million cells, of which approximately 1,8 million are macrophages. Over time, the constituents of breast milk change, playing less a role in protective immunity and more in nutritional value. In the case of breast milk, the antibodies they carry are mostly immunoglobulins A. They are important in protecting mucosal surfaces such as the intestine. When a baby’s digestive tract processes breast milk, maternal antibodies coat the baby’s gut, helping to fight gastrointestinal viruses. The antibodies in both colostrum and breast milk, which later replace colostrum, contain about 90% of immunoglobulin A in humans.
Antibodies that protect the baby but were made by the mother offer what is known as passive immunity. This relatively short-term help gives the baby’s immune system a chance to start working and complete development immediately after birth. As these antibodies weaken during the first few months of life, the baby’s immune system speeds up. In this way, mom and baby work together to protect the baby from the many pathogens to which she is exposed in the days and weeks after birth.
Also read: How does the immune system work?
The fetus – developmental problems
In most cases, prenatal development is normal, but many things, usually caused by genetic or environmental problems, can go wrong during this time.
Fetal development – genetic problems
Sometimes in the fetal period, genetic problems can arise that can affect both the present and future development of the fetus.
- Down syndrome (trisomy 21) – is the most common genetic anomaly during prenatal development. Down syndrome is caused by an extra copy of chromosomes 21 (meaning there are three chromosomes instead of the usual two) and occurs in 1 in 1000 babies. Common features of Down syndrome include flattened facial features, heart defects, and mental retardation. The risk of having a baby with Down syndrome increases with the age of the mother.
- Inherited Diseases – Many diseases can be inherited if one or both parents carry the disease gene. Examples of inherited diseases include sickle cell disease, cystic fibrosis, and Tay-Sachs disease. In order to prevent the development of genetic diseases in a child, genetic tests are carried out in advance to determine whether the parent is a carrier of the genes for a specific disease.
- Genetic Defects – A third type of genetic problem involves sex chromosomes. These include conditions such as Klinefelter’s syndrome (associated with the formation of an extra X chromosome) and Turner syndrome (caused by the missing or incomplete development of one of the X chromosomes).
Fetal development – environmental problems
Environmental variables can also play an important role in prenatal development. Harmful environmental factors that can affect the fetus are known as teratogens.
- Consumption of various substances by the mother – maternal substances may have catastrophic consequences for the fetus. For example, smoking is associated with low birth weight, which can result in a weakened immune system, respiratory problems, and neurological disorders. Alcohol consumption, in turn, can lead to Fetal Alcohol Syndrome, which is associated with heart defects, body malformations, and intellectual disability. Drug use also affects the fetus, and cocaine and methamphetamine, for example, are also associated with low birth weight and neurological disorders.
- The disease the mother suffers from – many diseases that the expectant mother suffers from can affect the fetus. For example, it is believed that the herpes virus is one of the most common such diseases and can affect the fetus, leading to deafness, cerebral edema, or intellectual disability. Women with the herpes virus are often encouraged to get pregnant by caesarean section to avoid transmission of the virus to the baby. Rubella and AIDS are also mentioned among other diseases that affect the fetus.
Many factors can pose a potential risk to a developing fetus. Some of them, including environmental problems, can be prevented or the risk minimized. When it comes to genetic problems, sometimes there is simply nothing that can be done. But always, early prenatal care can help mothers and babies cope with potential problems with prenatal development.
From what week can a child live outside the mother’s body?
A fetus is considered viable when it has reached a stage of development in which it is able to live outside the womb.
In general, the longer a fetus is in the womb, the more developed it becomes when it comes into the world. However, there are several other factors that determine when the fetus may survive outside the mother’s body.
- Fetal weight – Babies weighing 600 grams or more at birth are considered to have a greater chance of survival compared to those weighing less.
- Gender and number of fetuses – Some studies show that girls are more likely to survive at a younger age than boys. Likewise, single premature babies do better than premature twins.
- The care a woman receives before birth – sometimes corticosteroids, antibiotics, or magnesium during pregnancy (often given just before birth) can help increase your baby’s chances of survival after birth.
- The care your baby receives right after birth – infants born in hospitals with advanced neonatal intensive care units are more likely to receive the life-saving treatment they need right away.
It is difficult to determine the age at which a very early born child can survive. It is assumed that infants born before the third trimester (before the twenty-seventh week of pregnancy) have a chance of survival. However, it should be noted that such babies require life-saving interventions immediately after delivery and receive advanced care in intensive care units to survive. Even with the best possible care, they can experience short- and long-term problems.
According to a study by the American College of Obstetricians and Gynecologists (ACOG), a fetus may survive outside the mother’s body at the age of:
- 26 weeks – When the fetus reaches the last week of the second trimester, the chances of being viable are 86 to 89 percent.
- 25 weeks – fetuses at 25 weeks of age have an approximately 67 to 76 percent chance of surviving.
- 24 weeks – Doctors consider 24 weeks as the end point of potential viability, although at this age survival is still not guaranteed. According to the ACOG, the viability of the fetus after 24 weeks ranges from 42 to 59 percent. Although some studies have shown that the chances of survival are as high as 68 percent.
- 23 weeks – Babies born on 23 weeks usually have a 23 to 27 percent chance of survival.
- 22 weeks or earlier – the chances of being viable before 23 weeks are low, at around 5 to 6 percent.
See also: When a premature baby is born, that is, the difficult beginnings of motherhood
The fetus and the mother’s diet
Diet and nutrition play a key role during pregnancy. The diet must be varied and balanced, and the amount consumed should be moderate, especially in the first 1-3 months. Pregnant women should eat a diet consisting of the 5 main food groups in moderation, with particular emphasis on foods rich in folic acid, as this substance plays a key role in the production of various organs and brain cells of the fetus. There are also certain foods that should be completely avoided during the first trimester of pregnancy, including raw foods, foods that contain monosodium glutamate, foods high in sugar and fats. In addition, all drinks containing caffeine and alcohol should be discontinued during pregnancy.
However, unsaturated fats have a positive effect as they provide the body with energy and help reduce the presence of cholesterol, thus reducing the risk of heart disease. More importantly, the following types of unsaturated fats are beneficial for the development of the fetus: Omega 3 and Omega 6 fatty acids, which are classified as essential fatty acids (EFAs) because the body is unable to produce them on its own, which means that the diet is the only way for the body to gain access to them. Ocean fish and seaweed products contain Omega 3 fatty acids, while Omega 6 fatty acids can be found in safflower oil, sunflower oil and corn oil.
Additionally, DHA and ARA, which are long-chain unsaturated fats, are also crucial for the development of the fetal brain’s and eyeball cells. Omega 9 fatty acids play a key role in the development of the brain’s neuronal fibers (axon and dendrite), as well as in the sheath of neuronal fibers. It can be found in a variety of foods, including butter, peanut oil, lard, and olive oil.
Pregnant women should increase their intake of vitamins to help maintain a strong and balanced body, as well as support the growth and development of the fetus. Fruits and vegetables are the best sources of vitamins, but if women want to take vitamin supplements like vitamin A, B, C, D, E, and K, they should consult their doctor first. Moreover, in cases where pregnancy causes bouts of constipation, it is recommended to increase the amount of high-fiber foods. The situation is similar with the intake of minerals such as iron, which is a key component of hemoglobin in the blood of mother and child. Foods that contain high levels of iron include liver, red meat, egg yolk, and milk. However, most pregnant women will need to take iron supplements because the levels of iron in the food they eat are often not enough to meet their needs.
Another ingredient in the mother’s diet and how important for the health of the fetus is folic acid. This substance is crucial for the growth of the brain and central nervous system. In the case of a deficiency of folic acid in the fetus, the bones of the skull or spine may not heal properly. Therefore, it is recommended that women begin increasing their folic acid intake at least 3 months before conception by choosing green vegetables, soybeans, oranges, bananas, and folic acid-infused milk in their diets. Future mothers should also not forget about calcium, which plays a fundamental role in the development of bones and teeth. It can be found in milk and foods such as cartilage and small fish, and calcium supplements are also available.
Pregnant women should reduce their carbohydrate intake from flour, rice, and potato-based foods, and avoid sugary foods, especially sweet fruit. You should also limit white sugar and sodas, because in addition to increasing the risk of obesity, these foods can also increase the risk of developing diabetes in both mother and baby.