The average duration of pregnancy is about 280 days. During this period, a small
fertilized egg increases in size, is constantly divided into segments, from which organs and systems further develop. Organ systems at different stages of human embryo development undergo constant changes and ultimately the child becomes able to live outside the mother's body. But it takes a long nine months before a human embryo becomes viable for the environment.
Before the embryo begins to develop, fertilization of the egg must occur . For this, the follicle must mature, from which a suitable fetal egg will come out . During this period, called ovulation, fertilization must occur. Only after this begins the phased development of a new person. The stages of development of a human embryo are rather arbitrary, in fact, development occurs every second for nine months, but doctors conditionally divided the pregnancy into trimesters, each of which has its own formation cycle.
Developmental stages
1 month (1-4 weeks). The whole period there is a constant division of the cells of the fetal egg and its increase in size. From the cells, the internal organs are laid, and at the end of the period, blood circulation begins. The human embryo at this stage has the size of a grain of sand.
2 month (5-8 weeks). The umbilical cord develops and the formation of external organs and body segmentation into arms, legs, head occurs. The face of the baby begins to be indicated.
3 month (9-12 weeks). The embryo begins to move. The embryonic period is ending, the first trimester is coming to an end. From this moment it can be called the embryo of a person. He already has all the organ systems that will only further develop. He can now only determine the head section, the tail and the kidneys of the arms and legs, from which the limbs will further develop.
Month 4 (week 13-17). The second trimester begins . The face is more and more like a human: the ears are in place, the eyes continue to be closed. The limbs are already quite developed, but the fingers are still in their infancy.
5 month (18-21 week). The cartilaginous skeleton gradually hardens, and bones develop. The fetus begins to hear sounds, and subcutaneous fat begins to accumulate in it. Hands and feet develop, the baby has fully developed limbs.
6 month (22-26 weeks). The skin begins to function, hair appears on the head and face, the formation of nails. The genitals that are already developed are clearly visible. A human embryo becomes viable.
Month 7 (week 27-31). The kid can open his eyes. Now he is very mobile and mom can feel it. His hair grows fast and he is gaining weight. All organs continue their development, but he is already ready for life in the outside world.
8 month (32-36 weeks). The brain is actively developing, the stage of formation is completing. The nervous system becomes full and fully functional. Receptors in the tongue are gradually formed. Subcutaneous fat at this stage averages about 8 percent of body weight.
9 month (37-40 weeks). The baby is in the final position for the upcoming birth. Now he is ready and can be born at any moment.