Fetogenesis
The Fetogenese (of lat. Fetus , breeding, progeny 'and Alt Gr. Γένεσις (Genesis), creation, development') is the further development of the embryo after formation of the organs ( organogenesis ) to the birth, in which the development of organs ( morphogenesis ) and the differentiation of the tissues ( histogenesis ) takes place. In humans, it begins on the 61st day of pregnancy and thus replaces embryogenesis . In the 40th week of pregnancy, the signs of maturity of the fetus are fully detectable.
The period from the beginning of the 3rd month is called the fetal period, since the child is called the fetus from the end of the 8th week. It is characterized by rapid growth of the body. Development delays during this time can be made up later. This phase also reduces the risk of miscarriages and deformities of the fetus.
During the 3rd month the proportions of the face change as the eyes and ears gradually reach their final position. The limbs lengthen and the first muscle activities become possible, but the mother has not yet noticed them. From the 12th week post conceptionem (after fertilization) the sex of the fetus is visible.
In the 4th and 5th month there is a strong increase in length. Lanugo hairs are formed on the surface of the body . To date, it is not entirely clear whether this hairiness is an evolutionary relic or has a functional meaning. In addition, the sebum glands become active and the heart sounds can be heard. At least now, in the 5th month, the movements of the child are clearly perceived by the mother.
In the 6th month, the fetus is a little wrinkled: This is due to the fact that the skin is growing and the layer of fat under the skin is only slowly formed. The umbilical cord, around 50 centimeters long, is twisted in a spiral so that the fetus has sufficient freedom of movement in the amniotic sac. Above all, growth is now in the foreground, since the differentiation of the organs has largely been completed. This month the maturation of the sense of balance also begins.
In the 7th month the lungs become functional, so the fetus is viable as a premature birth at the 28th week.
Gradually the birth is approaching. In the last few weeks, the main focus is on growing the fetus and completing the vital organs.
In the 8th month, there is a strong increase in fat in the sub-conjunctival tissue, which tightens the previously wrinkled skin. In some cases, a special fat tissue, so-called brown fat tissue, is created especially in the area of the shoulder blades. Brown adipose tissue can convert fat into heat very quickly if necessary and is used to regulate the heat balance postnatally (i.e. after birth).
The olfactory sense is now also maturing. The liver grows faster and stores iron-containing compounds.
In the 9th month, the fetus sinks deeper into the maternal pelvis and thus reaches the corresponding birth position. Finally, after 280 days or 40 weeks, calculated from the first day of the last menstruation, or 266 days or 38 weeks, calculated from the time of fertilization, the birth takes place.