After the formation of internal organs in the ninth week of pregnancy, a human embryo is also called a fetus until birth. During this time, what is known as fetogenesis takes place. Various complications can occur during fetogenesis.
What is the fetus?
The term fetus is defined according to the gestational age and the formation of internal organs. Nevertheless, the beginning of fetogenesis is not clearly defined. Some authors consider its beginning in the thirteenth week of pregnancy. Others speak of a fetus as early as the ninth week of pregnancy. Moreover, the temporal limits for the corresponding terminology may vary depending on the stage of development. Another criticism is that there is no umbrella term for the same circumstance. Thus, one and the same living being is referred to as 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 is used for the unborn foetus from fertilization to birth. However, in humans, as mentioned above, the embryo is also referred to as the fetus or fetus from the formation of the internal organs.
Anatomy and structure
In the course of pregnancy, the shape of the fetus changes. From the beginning, it already has all the internal organs, but they do not fully mature until fetogenesis. From the 15th week of pregnancy, the fetus acquires an increasingly human appearance. Gradually, all sensory organs are formed. By the 34th week of pregnancy, the fetus is fully developed. It only continues to gain weight until birth. At this time, the unborn child already reacts to light and sound. It recognizes the mother’s voice. The taste buds are already fully developed. Furthermore, the fetus can also smell. At birth, all the nerve cells of the brain have already differentiated. The brain is still small. Its size after birth is about 0.35 liters. By adulthood, however, it reaches a size of 1.35 liters. This then no longer occurs through the increase of brain cells, but only through the insulating coating of the nerve conduits with myelin fat. The prenatal blood circulation of the fetus is connected to the maternal blood circulation via the placenta.
Development
Even before the onset of fetogenesis, organs are formed from the fifth to the eighth week of gestation. After its differentiation, the embryo is then called a fetus from the ninth to the eleventh week of pregnancy. In the 15th week of pregnancy, as mentioned above, its increasingly human shape becomes apparent. At this time, it is even possible to visually determine the sex of the fetus. 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 develops. From the 19th to the 24th week of pregnancy, fetal motility, cardiac activity, iris, cerebral cortex and the alveoli develop successively. By the 26th week, hearing is fully developed. The fetus can hear the mother’s heartbeat, breathing sounds and speech. It also learns to match the mother’s voice. By the 28th week, the fetus can smell, and by the 30th week, a surface film forms on its alveoli, allowing the baby to breathe after birth. By the end of the 34th week of pregnancy, all organs are fully formed, so the fetus only grows and gains weight until birth.
Diseases
The development of the fetus does not always proceed smoothly. The rapid formation of new body cells and differentiation of body organs requires well-functioning regulatory and control mechanisms. Complications can arise during pregnancy due to harmful environmental factors, hormonal imbalances and genetic causes. As a result, miscarriages, high-risk pregnancies and diseases in mother and child may occur. Harmful environmental influences primarily include alcohol and nicotine. Often the children tend to have mild to severe developmental disorders depending on the level of exposure and genetic factors. Environmental factors also include exposure of the mother to environmental toxins, radiation or stress. Some medications can also have a damaging effect.In the early 1960s, for example, the thalidomide scandal broke when it was discovered that thalidomide, a drug used to treat nausea during pregnancy, caused malformations in the fetuses. For this reason, a doctor should always be consulted to assess the risk when taking medication during pregnancy. 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 supplied with sufficient nutrients, vitamins and minerals. Malnutrition can lead to delayed development in the child. Chronic diseases of the mother are also sometimes responsible for risk pregnancies and developmental disorders of the child. Furthermore, 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 conditions occur repeatedly. The children require lifelong care. However, complications are still possible even in the last stage of pregnancy. For example, the fetus can be severely damaged during birth due to hypoxia. In this case, rapid emergency measures are required.
