After the formation of the internal organs in the ninth week of pregnancy, it becomes human embryo until birth also as fetus designated. During this time the so-called fetogenesis takes place. Various complications can arise during fetogenesis.
The term fetus is defined according to the gestational age and the development of the internal organs. Even so, the beginning of fetogenesis is not clearly established. Some authors see their onset in the thirteenth week of pregnancy. Others speak of a fetus as early as the ninth week of pregnancy.
The time limits for the corresponding terms can also vary depending on the level of development. It is also criticized that there is no umbrella term for the same issue. One and the same living being is called a zygote, morula, blastocyst, embryo, fetus or child, depending on the stage of development from the beginning of pregnancy to the birth process.
In general, the term embryo applies to the unborn womb from fertilization to birth. In humans, however, as already mentioned, the embryo is also called a fetus or from the formation of the internal organs fetus designated.
During pregnancy, the shape of the fetus changes. From the beginning it already owns all internal organs, which however only fully mature during fetogenesis. From the 15th week of pregnancy, the fetus begins to look increasingly human. Gradually all sense organs develop.
The fetus is then fully developed by the 34th week of pregnancy. He only gains weight until birth. At this time the unborn child is already reacting to light and sound. It recognizes the mother's voice. The taste buds are already fully developed. The fetus can also smell. At birth, all of the brain's nerve cells have already differentiated.
The brain is still small. Its size after birth is approximately 0.35 liters.By the time it reaches adulthood, however, it reaches a size of 1.35 liters. This then no longer happens through the increase in brain cells, but only through the insulating sheathing of the nerve lines with myelin fat. The prenatal bloodstream of the fetus is connected to the maternal bloodstream via the placenta.
Even before the start of fetogenesis, the organs develop from the fifth to the eighth week of pregnancy. After it has been differentiated, the embryo is called a fetus from the ninth to eleventh week of pregnancy. In the 15th week of pregnancy, as already mentioned, his increasingly human form emerges.
During this time it is even possible to determine the gender visually. From the 18th week the fetus opens its mouth and swallows amniotic fluid. The digestive system begins to work. At the same time, the sense of taste also develops. From the 19th to the 24th week of pregnancy, the mobility of the fetus, heart activity, iris, cerebral cortex and the alveoli develop one after the other. Hearing is fully developed by the 26th week. The fetus can hear the heartbeat, breath sounds, and speech of the mother. He also learns to assign the mother's voice.
From the 28th week the fetus can smell and from the 30th week a surface film forms on its alveoli, which enables the child to breathe after birth. By the end of the 34th week of pregnancy, all organs are fully developed, so that the fetus only grows and gains weight until birth.
The development of the fetus does not always go smoothly. The rapid formation of new body cells and differentiation of the body organs requires well-functioning regulatory and control mechanisms. Harmful environmental factors, hormonal malfunctions and genetic causes can lead to complications during pregnancy.
As a result, miscarriages, high-risk pregnancies and illnesses can occur in both mother and child. The main harmful environmental influences include alcohol and nicotine. Often the children tend to have mild to severe developmental disorders, depending on the degree of stress and genetic factors. The environmental factors also include exposure of the mother to environmental toxins, radiation or stress. Some drugs can also be harmful.
In the early 1960s, for example, the so-called Contergan scandal occurred when it was discovered that the drug Contergan against pregnancy sickness caused deformities in the fetuses. Therefore, if you are taking medication during pregnancy, you should always consult a doctor to assess the risk. Some infectious diseases such as rubella, toxoplasmosis or listerosis are also very dangerous for the fetus during pregnancy. As a result, the child may suffer from physical and mental limitations for life.
It is also important for pregnant women to ensure that the body is adequately supplied with nutrients, vitamins and minerals. Malnutrition can lead to delayed development in the child. Chronic maternal illnesses are also sometimes responsible for high-risk pregnancies and developmental disorders in the child.
In addition, genetic disabilities and developmental disorders such as trisomy 21 (Down syndrome), trisomy 13 (Pätau syndrome), Marfan syndrome (connective tissue disease), Turner syndrome and many other diseases occur again and again. The children require lifelong care. But complications are still possible in the last phase of pregnancy. For example, the fetus can be seriously damaged during birth from an insufficient oxygen supply. In this case, urgent emergency measures are required.