The fetus is a human embryo in the period of intrauterine development , starting from the 9th week and up to the moment of birth. At the 9th week of development, the fetus in appearance takes on the features of the human body. In its structure, the head, body, rudiments of limbs, eyes, nose, and mouth are clearly distinguished. Fruit length 3-4 cm.
By the end of the 3rd obstetric month (obstetric month - 4 weeks, or 28 days) of fetal development, the length of the fetus reaches 8-9 cm; his weight - 25-35 g. The head is about half the length of the fetus. Well differentiated limbs. Differences in the structure of the external genitalia are revealed.
By the end of the 4th month the length of the fetus is 15-16 cm; weight - 120 g. Clearly distinguishable gender . The skin is thin, shiny, there is no subcutaneous fat layer. The umbilical cord is attached to the abdominal wall above the bosom.
By the end of the 5th month the length of the fetus is 25 cm; weight 300-320 g. On the skin appears fluff; in some places, subcutaneous fat is deposited; slightly emitted a cheese lubricant. Nails are distinguishable on the fingers.Go
By the end of the 6th month, the length of the fetus reaches 30 cm, weight - 600-650 g. The fetus is not viable outside the mother's body. By the end of the 7th month, the length of the fetus is 35 cm, weight within 1000 g. The skin is red, wrinkled, which gives the fetus a “old” look; subcutaneous fat layer is still poorly developed. Hair is up to 0.5 cm long on the head. The umbilical cord is attached below the middle of the distance between the xiphoid process and the symphysis. Auricles are soft. Nails do not reach the end of the fingers. In boys, the testicles did not descend into the scrotum. Girls have small labia not covered with large lips. The fetus is premature and physiologically immature, usually dies after birth; survives only in isolated cases with particularly good care (see Cuvez).
By the end of the 8th month, the length of the fetus reaches 40 cm; weight - about 1600 g. The fetus after birth is viable, but requires special care.
By the end of the 9th month, the length of the fetus reaches 45 cm, weight - 2400 g. The skin is pale pink; the fluff almost completely disappears; the nails reach the tips of the fingers; the subcutaneous fat layer is well developed. The testicles usually descend into the scrotum. The fruit is quite viable. By the end of the 10th month, the fetus becomes full-term, born mature (see Newborn ).
The size of the head of a ripe fetus
1. The direct size (from the nose to the occiput) 12 cm long, the circumference of the head in the direct dimension is 34-35 cm.
2. Large oblique size (from the chin to the most distant point of the occiput) —13.5 cm, circumference, respectively 39–41 cm.
3. Small oblique size (from the suboccipital fossa to the middle of the large fontanel) - 9.5 cm, circumference - 32 cm.
4. The vertical size (from the region of the hyoid bone to the middle of the large fontanel) is 9.5 cm, the circumference is 32 cm.
5. Large transverse size (distance between parietal mounds) - 9.5 cm.
6. Small transverse size (the distance between the most distant points of the coronal suture) - 8 cm.
On the body of a mature fetus, the following dimensions and circles are distinguished: 1) the transverse size of the hanger is 12 cm long and 35 cm in circumference in this dimension; 2) the transverse size of the buttocks is 9–9.5 cm, with a circumference of 27–28 cm, respectively.
To determine the age of a born fetus by its height, one can use the Haase formula. According to it, in the first half of pregnancy, the length of the fetus in centimeters corresponds to the number of months of pregnancy squared, and from the 6th obstetric month to the product obtained from multiplying the number of months by 5.
A fetus is a human embryo in the period of intrauterine development, starting from the 9th week and up to the moment of birth.
Fig. 1. Typical age-related changes in the proportions of different parts of the body: 1 - in an embryo up to 2 months; 3 - at the fetus of 4 months; 3 - in the newborn.
Fetal development . By the end of the 8th week after fertilization, the embryo length from the crown to the buttocks reaches 20 mm, and it becomes characteristic of
human traits: distinct parts of the head, torso and limbs are clearly defined. The head in the embryonic period has the same length as the torso; further, these ratios change (Fig. 1), complete organogenesis occurs.
There appear centers of skeletal ossification, which are often defined in the lower and upper jaws, in the spongy part of the occipital bone, in the clavicles, in the diaphysis of the thigh and shoulder. During the fruit period, the growth of parts already formed in the first two months of development occurs. The length and weight of the fetus - the main indicators of its age (Fig. 2).
Fig. 2. Curves of body height, increase in its surface and weight during antenatal life (according to Boyd).
By the end of the 3rd obstetric month (the obstetric month is 4 weeks or 28 days), the fetal intrauterine development is 8–9 cm long and weighs up to 40 g, almost half of the body length falls on the head. The external genitals begin to differentiate. On the fingers of the upper and lower extremities are determined by the beginnings of nails. There are very weak movements of the limbs, which the mother has not yet felt.
By the end of the 4th month, the fetus has a length of 16 cm, weight up to 120 g. According to external signs, its sex is clearly visible. The skin is red, thin, smooth, and superficial vessels shine through it. The ossification of the skull occurs. Ends the formation of the muscular system. The navel is located at the pubis.
By the end of the 5th month, the length of the fruit is 24–26 cm, of which one third is on the head, the weight is 280–300 g. The skin is dark red in color, and fat is deposited in places in the subcutaneous tissue. The sebaceous glands appear, the discharge of which, mixing with the exfoliating epidermis, is deposited on the forehead, back and limbs, forming a whitish, so-called cheese-like lubricant. The skin, starting from the head and face, especially in the eyebrows, is gradually covered with thin delicate hair. In a five-month-old fetus, intestinal-colored feces (meconium) are formed in the intestines. During auscultation of the abdominal wall of a pregnant woman, it is possible to listen to fetal heart sounds. At 18-20 weeks, the examination determines the energetic movements of the fetus; they are felt by the mother herself. If the fetus is born during this period, then it makes weak respiratory movements.
By the end of the 6th month, the length of the fetus reaches 30–31 cm, weight 600–700 g. The head is disproportionately large.
A six-month-old fetus makes breathing movements, moves limbs energetically, but usually dies soon. During this period of intrauterine life, all the organs of the fetus are so developed that in rare cases, under exceptionally favorable conditions, it can develop even in utero.
By the end of the 7th month, the length of the fetus is 35 cm, weight is 1000 g. It has a senile appearance due to insufficient development of subcutaneous fatty tissue. The skin is red, covered with cheese-like grease and downy hair. On the head, hair is 0.5 cm long, the eyelids are somewhat glued together, the pupillary membrane exists as a residue at the edge of the pupil, the auricles are soft and tight to the head, the nails do not reach the tips of the fingers. In boys, the testicles did not descend into the scrotum, in girls, the labia majora are poorly developed, and between them the clitoris and the labia majora significantly protrude. A fetus born during this period can survive with the creation of particularly favorable conditions.
By the end of the 8th month, the length of the fetus reaches 40 cm, weight is 1500-1600 g. The skin is still red, covered with fuzz, but smoother than that of a seven-month-old fetus. The pupillary membrane is absent. Prematurely born fruit of this period with proper care can survive.
By the end of the 9th month, signs of prematurity disappear, and signs of maturity are becoming more pronounced. The skin loses its red color and becomes pink. Due to the abundant deposition of subcutaneous fat, body shapes are rounded, the face loses its wrinkled appearance, the skin becomes smooth, the fluff thins, the hair on the head becomes longer, the edge of hairiness on the forehead protrudes. The cartilages of the nose and ears become denser, the nails reach the end of the fingers. In boys, both testicles are descended into the scrotum. A fetus born during this period is completely viable, screams loudly at birth, opens its eyes; clearly expressed sucking reflex.
During the 10th month, signs of prematurity finally disappear and the full development of the fetus begins. The fetus becomes full-term. Its length is 49–50 cm, weight is 3200–3500 g. The skin is pink, smooth and covered with fuzz only in the region of the shoulder girdle. The nails protrude beyond the edges of the fingers. The length of the head is a quarter of the entire length of the fetus. Born mature fruit is very active, moves its limbs, makes a loud cry. Respiratory, circulatory and digestive organs are developed to such an extent that they fully provide for the possibility of extrauterine existence.
To determine the age of the fetus by its length (growth), measured on a horizontal stadiometer with the baby extended, various schemes have been proposed. The most accepted is the Haase scheme, in which in the first 5 months the length of the fetus in centimeters corresponds to the number of months of pregnancy squared, and in the last 5 months - multiplied by five.
Numerous factors affect the height and weight of the fetus: age and physical condition (height, weight) of parents, repeated pregnancy, sex of the fetus, nutrition and living conditions of the mother. With the age of the mother and the number of pregnancies, the size of the fetus also increases. The average weight and height of boys is more than girls. Increased nutrition of a pregnant woman, especially with increased use of vitamins, contributes to weight gain and fetal growth.
The age of the fetus can be determined by radiography of the points of ossification in its skeleton. On the 2nd – 3rd month of intrauterine life, the fetus develops most of the ossification centers (Fig. 3).
The human embryo's nervous system begins to develop early, at the end of the first month of life there are main sections of the brain. In the same period, the laying and formation of the spinal cord and the autonomic nervous system are observed. In the future, there is a complex process of differentiation.
The body of the fetus is extremely rich in water; its content in a six-week embryo is 97.5% of the total body weight. The water content in the tissues of the fetus at the time of birth is 73.9%.
Breath of the fetus . Oxygen from mother to fetus is transmitted through the placenta. In the fetus, intrauterine respiratory movements are observed under physiological conditions of development, which can be determined by the vibrations of the abdominal wall of a pregnant woman, starting from the 6th month, or recorded using a kymograph. These respiratory movements are superficial, they occur with a closed glottis, and aspiration of amniotic fluid does not occur. Intrauterine respiration as a result of the known negative pressure that forms in the chest cavity of the fetus during each respiratory movement promotes aspiration of blood from the placenta toward the right half of the heart. Intrauterine respiratory movements prepare the neuromuscular mechanism of fetal respiration to the conditions of extrauterine life. The lungs of the fetus begin to function only from the moment of the first extrauterine breath.
The metabolism between the mother and the fetus is carried out using the placenta (see) due to the action of very complex mechanisms.
Excretory activity of the kidneys in the fetus begins with the 5th month. Urine is poured into the cavity of the amnion, being one of the sources of amniotic fluid. However, the excretory function of the kidneys is not necessary, since decay products are eliminated through the placenta. Fetal urine is hypotonic, contains 130-170 mg% of chlorides, a small amount of urea and uric acid.
During the period of intrauterine life, especially in the first 7–9 weeks of pregnancy, various pathogenic factors (hypoxia, overheating, hypothermia, ionizing radiation, various chemical compounds, pathogenic microbes and their toxins, etc.) can affect the fetus directly subject to penetration through the placental barrier damaging factors or exerting an indirect effect through the mother's body. These factors cause a variety of changes in the fetus that may violate the conditions of its development and vital activity (see Asphyxia, Fetopathy, Embryopathy).
See also Germ.