Definition
Fetus or also fetus means translated “descendant”. A fetus is an unborn child in the womb. After fertilization, the developing child is called an embryo.
When the internal organs are developed, the official term is then fetus. The foetal period begins from the 9th week of pregnancy and ends with birth. After birth, the foetus is called an infant.
Development
Development of the embryoIn the first and second week of pregnancy there is no pregnancy in the classical sense. Although the egg is fertilised, it has not yet reached the uterus into which it is implanted. The implantation in the uterus occurs around the third week of pregnancy.
The chromosomes, on which the physical characteristics are stored, are already determined at this time. For example, the color of the eyes or hair, the sex is already genetically determined, but of course not yet recognizable. 2 weeks after fertilization of the egg, cell division is accelerated.
After fertilization in the 3rd week of pregnancy, the fertilized egg cell divides several times. Within a short time, a larger cell cluster is formed, while the body prepares the uterus for implantation of the egg. Once the cell cluster has reached the uterus, it divides into 2 different areas.
The placenta develops from one part. It burrows deep into the mucous membrane of the uterus. It is from the placenta that the embryo and later the foetus obtains its nutrients throughout the entire pregnancy.
The other part of the cell cluster develops bit by bit into the embryo. There is a vital connection between the developing child and the placenta: the umbilical cord. Parts of the placenta form the pregnancy hormone Beta HCG.
It signals to the body that pregnancy has occurred and that ovulation does not have to take place. Most pregnancy tests are carried out using this hormone. After implantation, the cell cluster is initially divided into two different layers, from which the organs are later formed.
This is called the outer and inner cotyledon. Endoderm and ectoderm. The outer cotyledon of the future fetus is used to form the nervous system, the sensory epithelium, from which eyes, nose and ears are formed, skin and hair systems, sweat glands, milk glands and enamel.
From the inner cotyledon, the thyroid gland, liver and pancreas, tonsils and thymus and the digestive tract are formed. After these two cotyledons are attached, a third middle cotyledon (endoderm) is formed. By appropriate invagination, the so-called neural tube is formed, from which the largest part of the brain and nerves are formed.
The middle cotyledon is divided into 2 larger symmetrical cell blocks. The following organs are formed from them: spine and vertebral bodies, bones and cartilage, the heart, muscles, connective tissue, blood and lymph vessels, urogenital system and most internal organs. The embryo is now about 2 mm in size and has already nested in the uterus.
From now on, growth and organ development begins. This stage of development is called the embryonic phase. From the 22nd day, i.e. in the 5th week of pregnancy, the heart of the embryo begins to beat.
Due to its small size, it must beat much faster than in adults. On average, it beats 120-160 times per minute. However, the heartbeat can only be detected on the ultrasound from the 8th week.
In addition, the head and trunk are already in place by the 5th week. The size of the embryo is about 4 mm. The neck and head can already be seen on the ultrasound.
Eyes and ears are dimly visible. Neck and thoracic vertebrae are clearly visible in the ultrasound during pregnancy. In the further course of the pregnancy, the child’s rib cage is formed from them.
The embryo now has a size of about 5 mm. In the following weeks, it will rapidly increase in size. At this time, eyes and nose can be clearly seen.
The mouth is also clearly visible as well as the brain system. Hands and feet look not yet fully developed and are not yet proportional to the rest of the body. Vessels shimmer through the thin skin (not visible in the ultrasound) and the attached muscles develop quickly.
At this point, the embryo begins to move. The embryo is in a bent position. The head towers above almost the entire body, which is relatively small compared to the head.
It now has a size of about 1.5 cm. The toes and fingers are now clearly visible and fully developed. The proportions begin to gradually adjust.Heartbeat and pulse are now clearly visible in the ultrasound.
Many other organs are already fully established and functional. For example, both kidneys are already in use and produce urine, which is released into the amniotic fluid. The stomach begins to take up its activity and the upper body slowly straightens up.
The joints of the upper and lower extremities begin to form and ensure that the embryo stretches and bends the legs and arms. At this stage of pregnancy, however, movements are still uncontrolled and uncoordinated. The embryo has survived the first stage of development.
The official term is now fetus. Despite the rapid development, the fetus is still in a vulnerable phase at this time. Abortions or miscarriages and recognizable malformations may occur.
Numerous complications can occur. During the 9-10 weeks, the internal organs are fully developed. The brain is completely covered by the skull bone.
With the formation of the brain and the nerve tracts, the foetus can perceive external sensory impressions. It can thus perceive vibrations, cold, heat and pain. Furthermore, the fetus is practically in constant movement and kicks with its arms and legs.
The size of the fetus is now about 4-5 cm. In addition to the complete organ system and training, the external sexual characteristics (testicles and penis in boys, the vagina in girls) have now also developed. This is a time that is probably longed for by all expectant parents, because from now on it is possible to tell by means of an ultrasound examination whether it will be a boy or a girl.
However, at this point in time this statement is not yet certain. You can see the sex more clearly in the 20th week of pregnancy. Further developmental stages of the 11th week of pregnancy are the enclosure of the rib cage around the internal organs to protect them.
At this time all organs are created and either still in development or the development is already completed. Tooth roots are located in the upper and lower jaws just like hair roots. This is the end of the first third of pregnancy (1st trimenon) and thus the “dangerous phase” for the foetus.
Statistically speaking, from now on the fetus is less threatened by serious events, such as an abortion or malformations. Miscarriages can still occur, but since the majority of miscarriages are due to chromosomal damage, which particularly affects the first stages of development, the risk is significantly reduced. In most cases, the expectant parents also inform their relatives and friends at this time.
It is still important to have appropriate preventive medical checkups during pregnancy with an ultrasound and to continue to secure the pregnancy in order to recognize dangerous progressions at an early stage. The fetus is now about 5 cm long, moves energetically and is active. It uses its arms and legs to move and moves its head.
The size of the fetus is measured by an ultrasound examination using a connecting line between the skull and the rump (buttocks of the fetus) (skull-rump length). The weight of the fetus is also calculated by ultrasound and is usually about 16 grams in the 12th week of pregnancy. Although the head is still disproportionately large, it slowly begins to adapt to the body.
The eyes also move to the front of the head. At this time of pregnancy, the fetus is still completely blind. Throughout the pregnancy, the umbilical cord, which is connected to the mother via the placenta, supplies nutrients and oxygen.
Although the placenta is also a filtering organ, some toxins are allowed to pass through. It is therefore very important that the expectant mother does not consume alcohol or smoke. Even if the mother is taking various medications, a doctor should be consulted beforehand and asked about the safety of taking them.
On the one hand, the amniotic fluid in the amniotic sac acts as a protective buffer and thus protects the fetus from knocks and movements, but it also serves as a “waste water container”, so to speak, because the fetus’ urine is released into the amniotic fluid. At the time of the 12th week of pregnancy, the female external sexual organs also become visible. Here, too, no definite diagnosis can be made as to whether it will be a boy or a girl.
The gynecological check-up during pregnancy takes place every 4 weeks until the 32nd week of pregnancy. After that, the interval is shortened to every 2 weeks. Within one pregnancy, 10-12 examination appointments are thus scheduled.In addition to the ultrasound examination of the fetus, urine and blood pressure checks of the mother are performed, as well as weight checks and general physical examinations of the mother.
Furthermore, in advanced pregnancy, heart sounds and the position of the child are also determined. A total of three major ultrasound examinations are planned during pregnancy. The first takes place between the 9th and 12th week of pregnancy.
This is the basic examination. The second examination, which can also be performed as an extended ultrasound examination, should be performed between the 19th and 22nd week of pregnancy. The last one should be carried out between 29 and 32 weeks of pregnancy. In case of problems or complaints, an ultrasound can of course be performed at any time.
