The baby develops in the womb in about 40 weeks. In the early stages, the human embryo bears many similarities to animal embryos. In its further development, it undergoes a small evolution.
First week: the embryo intensively divides and descends into the uterus, implanted in its wall, connecting with the blood vessels of the organ. At 2 weeks, the umbilical cord, placenta and neural tube begin to form. At 3 - the respiratory organs, digestion, secretions, circulatory and nervous systems begin to form. By the end of 3 weeks, the heart may be pulsating. At 4 weeks, a notochord appears - the future spine, the neural tube is formed. The limbs are highlighted, muscle tissue is gradually formed.
At week 5, organ formation continues. There is an upper lip, nasal cavity on the face. At 6 - the brain continues to develop, eyes that are not covered by eyelids are visible. The upper limbs are extended. The heart has already been divided into chambers, there are primary kidneys, the gastrointestinal tract is gradually divided into sections. At 7 - the umbilical cord is formed, and blood circulation is established between the embryo and the placenta. On the upper limbs there are connected fingers, the eyes are protected by eyelids. The nose and ears begin to form.
At 8 - the improvement of organ systems continues. The body of the embryo grows rapidly. At week 9, the musculoskeletal system develops, joints and cartilage tissue are formed. There are only erythrocytes in the blood, the brain is improving, the endocrine system is developing. At week 10, the tail disappears, buttocks are formed. The fetus responds to stimuli with movements, the formation of the diaphragm ends.
At week 11, the organ of vision improves. At 12 - the genitals develop, the intestines are stretched, the brain is close in structure to the brain of an adult. White blood cells appear in the blood, the fetus imitates breathing movements. At 13 weeks, the body becomes more proportional. At 14 - a face is already visible, a fluff appears on the body. The excretory system has been formed, the endocrine and reproductive systems are being improved, it is already possible to determine the sex of the baby.
At the 15th week, blood vessels grow and strengthen, fingers are formed. At 16 - all organs and systems complete their formation. The child's skin is very thin, there are eyebrows and eyelashes, nails, and facial muscles are developed. At 17 weeks, the fetus reacts to sound. At 18 - a sleep and wakefulness regime is formed, basically the fetus is asleep. At 19 - the body overtakes the head in growth, the fetus often moves, the blood composition improves. At week 20, the blinking reflex appears, the fetal movements are already more coordinated.
At 21 weeks, the layer of subcutaneous fat increases, the fetus sleeps less. At 22 weeks, his body becomes proportional, the spine is already fully formed. At 23 - skin pigment is produced, the skin is covered with lubricant. The fetus actively swallows amniotic fluid. At week 24, hearing and vision are well developed, an emotional connection with the mother is established. On 25 - the skin is elastic, fewer folds, more subcutaneous fat. The bone marrow develops, the lungs are formed. At the 26th week, the sense of smell appears, the girls' genitals finish forming.
At week 27, metabolism begins to work. At 28 weeks, a prematurely born fetus is considered viable. The fluff remains on the back and shoulders, the hair darkens. One of the cerebral hemispheres functions more actively. At the 29th week, the child begins to experience a deficit of free space, the improvement of organs continues. At 30 - he occupies a certain position, the lungs and cerebral cortex continue to develop.
At 31 weeks, the fetus again sleeps a lot, the volume of its brain increases. At 32 - the skin brightens, folds disappear. At 33 weeks, the layer of adipose tissue continues to increase, the brain completes its formation. At 34 weeks, hair grows intensively, bones are strengthened.
At 35 weeks, the baby is rapidly gaining weight. At 36 - all his organs and systems are completely ready for extrauterine existence. At 37 - the skin thickens, there is more and more fatty tissue. Cartilage is more elastic. At 38 weeks, the baby is ready for birth. At 39 - the lowering of the fetus begins, metabolic processes in the placenta worsen. Weight gain - 30 g per day. Childbirth occurs at 40 weeks.