The birth of a child is a very complex and responsible process. Every expectant mother wants to know how the embryo develops week by week. After all, this action is reliably hidden from human eyes, but has been carefully studied by scientists.

So, embryo development week by week

The first few hours after conception. The sperm penetrates the egg and fertilization occurs. Until eight weeks, the resulting fetus is called an “embryo.”

1-2 weeks. Something active is happening. The embryo moves along the fallopian tube, enters the uterus and by the end of the second week is fixed on its mucous membrane. already at this stage, and it depends on the set of chromosomes that contained the sperm that fertilized the egg.

3-4 weeks. Despite the fact that the fetus is very tiny, its heart is already beginning to pulsate. The nervous system, skeletal and muscular, gradually emerges. As a rule, during this period a woman begins to guess about her pregnancy, since there is no menstruation.

5th week. The length of the embryo is about 6-9 millimeters. His brain and spinal cord are already developing, and the formation of the central nervous system is taking place. The heart becomes detached, arms, legs, and a head appear with holes for the eyes, mouth and nose.

6th week. The placenta is formed. During this period, it serves the baby as the liver, lungs, kidneys, and stomach.

7th week. The length of the embryo already reaches 12 millimeters, and the weight is 1 gram. The fetus has its own and begins to move, but due to its tiny size the woman does not feel the movement in any way.

8th week. pregnancy proceeds dynamically and systematically. The embryo has already formed a body. You can distinguish the face, nose, ears. The nervous system continues to improve and the skeleton continues to grow. The first rudiments of the genital organs appear.

9th week. The baby's entire body already has sensitivity. He can touch himself, the umbilical cord.

10-13 weeks. This stage is one of the most important in the process since the nervous system and most organs are actively developing. The fetus begins to make the first swallowing movements. As a result of the active development of the skeleton, its size rapidly increases, which entails the growth of the pregnant woman’s tummy. During this period, the baby can already hear and the vocal cords are formed.

14-16 weeks. The kidneys and bladder begin to function, the fetus takes its first breaths and exhales, and opens its eyes. Significantly increases

17-20 weeks. Photos of the embryo week by week during this period show that all parts of the body are already clearly visible. The baby opens his mouth and blinks. Due to the fact that its dimensions already exceed 14 centimeters, the expectant mother begins to feel light tremors.

21-25 weeks. The weight of the fetus increases rapidly, and the first fat deposits appear. The baby's lungs are quite developed, and if he is born prematurely after 23 weeks, there is a high chance of survival with intensive care. The baby's heartbeat begins to be heard if you put your ear to the pregnant woman's belly.

26-30 weeks. The development of the embryo week by week during this period is very active. Thus, a sucking reflex is formed, the first hairs on the head and eyelashes may appear, and nails grow.

31-35 weeks. The baby's skin becomes thicker. When he is awake, he opens his eyes and closes them when he sleeps. The brain is actively developing, the number of convolutions is increasing. The lungs are fully formed and the grasping reflex is developing.

36-40 weeks. The period of waiting and preparation for childbirth. Starting from this moment, you can expect the first contractions - harbingers. the cervix shortens. The body is preparing for childbirth. At this stage, the development of the embryo is completed by weeks. The baby becomes quiet and pushes less, because due to its significant size it becomes cramped for him. From 38 weeks the baby is considered full-term.

There are 4 periods in human embryogenesis:

1. Beginner(1 week of development, until the implantation of the embryo into the uterine mucosa).

2. Embryonic(2-8 weeks).

3. Prenatal(9-12 weeks). =larval in animals

4. Fertile(13th week – birth). =metamorphosis

During the embryonic period, gastrulation, blastulation, and neurulation occur. Intense organogenesis and anatomical formation of organs take place in the prefetal stage. The fetal period is characterized by the creation of a fetus under the protection of the membranes.

In the initial period there is zygote– 1 cell of the embryo, in which individual sections of the cytoplasm are determined, DNA and proteins are synthesized. The zygote has a bisimitric structure. Gradually, the relationship between the nucleus and the cytoplasm is disrupted, resulting in stimulation of the process of division - crushing

The cleavage stage is a period of intense cell division. The size of the embryo does not increase, and synthetic processes are active. Intensive synthesis of DNA, RNA, histone and other proteins occurs.

Crushing performs the following functions:

A sufficient number of cells necessary for the formation of tissues and organs are formed.

Redistribution of yolk and cytoplasm between daughter cells. The 1st and 2nd fission furrows run along the meridian, and the 3rd along the equator. Closer to the animal pole.

The plan of the embryo is determined - the dorsal-ventral axis, the anterior-posterior axis.

Nuclear-cytoplasmic relationships are normalized. The number of nuclei increases, but the volume and mass remain the same.

Gradually, division slows down.

In a woman, one day after fertilization, fragmentation begins in the second third of the oviduct. Simultaneously with this process, the zygote moves along the oviduct to the uterine cavity. Two types of cells are formed: smaller ones, which later give rise to auxiliary tissue - trophoblast, and larger cells - embryoblast - “embryo rudiment”, which will give rise to all the cells of the body and the cells of some auxiliary parts.

On 6-7 day After fertilization, the human embryo measures 0.5 mm and consists of 200 cells. It begins to attach to the inner wall of the uterus, penetrates the uterine mucosa, and implantation occurs. Within 24 hours, it is half immersed, and after another day, it is completely immersed. Then the trophoblast develops powerfully - villi and outgrowths are formed that come into contact with the mother’s blood, receiving nutrients and supplying them to the embryo.

On 2 weeks extraembryonic parts grow, i.e. those parts that are formed by the embryo, but first play an auxiliary role - amnion, chorion, yolk sac. These are provisional organs - coenogenetic structures that do not take part in the formation of an adult organism. The cellular material from which the embryo develops is the embryonic shield. In the early stages, preparatory work is underway; it is not the embryo itself that develops, but parts that create the necessary conditions for the existence of the embryo and provide the functions of respiration, nutrition, excretion of metabolic products, creating a liquid environment around the embryo to protect it.

3 week– the placenta is formed, Greek. "Cake". Consists of 2 parts - embryonic and maternal. Germinal – trophoblast and some other tissues (chorion – Greek “shell, afterbirth”). Maternal - highly modified uterine mucosa. In it, blood vessels are destroyed, connective tissue is loosened, and the epithelium is destroyed. The chorionic villi “bathe” in maternal blood. The area of ​​the placental plexus is 5 square meters, and the total length of the chorionic villi is 5 km. The maternal and embryonic organisms do not have a common blood flow, the blood does not mix. Nutrients pass through the walls of the chorion. In a 3-week-old embryo, umbilical vessels appear, growing into the walls of the chorion and performing functions. Food.

4 week. The dimensions of the embryo together with the chorion are 5-7 mm. A new stage begins. The body of the embryo is separated from the extraembryonic parts. The embryo rises above the amniotic fluid, with which it is then connected only by the umbilical vessels. During embryonic development, a yolk sac appears early in humans - the first hematopoietic organ that stores and processes yolk, the first organ of respiration and nutrition. Primary germ cells begin to form in the yolk sac. There is an intestine that is blindly closed on both sides. The liver is a hematopoietic organ. The heart is beating. By the end of 4 weeks there is a rudiment of the respiratory system. Sizes up to 30mm.

The intestines grow in length, do not fit in the straightened state and begin to bend. By the end of 4 weeks, shoulder blades appear on the sides. Nerves and muscles grow into them - future arms and legs. By the end of the week, there is differentiation into parts; by the 5th week, sections of the embryo protrude on the sides of the back of the head and neck - 4 pairs of gill slits are formed, parts of the foregut protrude from the inside, forming 4 gill pouches. There is no connection between the gill slits and the gill pouches. The middle ear is formed from 1 pair of gill slits. The rest are the thyroid and thymus glands.

From 4 weeks the nervous system begins to form. Formation of the neural tube (neural plate - neural groove - neural tube). At the anterior end of the neural plate, 3 brain vesicles appear; at week 6, there are already 5 brain vesicles that correspond to parts of the brain; auditory vesicles, optic cups, and olfactory pits appear. Mesoderm differentiation occurs. A tail is formed (day 34) up to 10 mm.

At 2 months The primary sex glands are formed, where the primary sex cells migrate from the yolk sac.

On 8 weeks rapid development of the amniotic membrane and accumulation of fluid occurs.

9-10week– kidney formation, nephrons are formed throughout embryogenesis and another 20 days after birth.

week 7– formation of dental plates.

Start 3 months. The fruit is formed. Within a month, the tail disappears (cell death under the influence of lysosomal enzymes), leaving rudimentary vertebrae. The head is ahead of the body in development, then the proportions are restored.

Start of 4 months. Sizes 20-22cm. the muscular system is formed and begins to move.

5 month. The entire body is covered with hair.

The upper limbs grow faster than the lower ones and appear earlier.

Division of the zygote and formation of germ layers. a - fertilization: 1 - sperm, 2 - egg; b,c,d - fragmentation of the zygote; e, f - blastula: 1 - embryoblast; 2 - trophoblast; g.e.i - formation of germ layers: 1 - endoderm, 2 - ectoderm, 3 - mesoderm.

Individual development, or development in ontogenesis, occurs during all periods of life - from conception to death. In human ontogenesis, two periods are distinguished: before birth (intrauterine, prenatal; from Greek natos - born) and after birth (extrauterine, postnatal). During the prenatal period, from conception to birth, the embryo (embryo) is located in the mother's body. During first 8 weeks the basic processes of formation of organs and body parts occur. This period is called embryonic, and the body of the future person - embryo(embryo). Beginning from 9th week, when the main external human features have already begun to appear, the organism is called fruit, and the period is fertile.

After fertilization (fusion of sperm and egg), which usually occurs in the fallopian tube, the fused germ cells form a single-celled embryo - a zygote, which has all the properties of both sex cells. From this moment the development of a new (daughter) organism begins.

First week of embryo development- This crushing period(division) of the zygote into daughter cells (Fig. 23). During first 3-4 days the zygote divides and simultaneously moves along the fallopian tube towards the uterine cavity. As a result of division of the zygote, a multicellular vesicle - blastula with a cavity inside (from the Greek blastos - sprout). The walls of this vesicle consist of two types of cells: large and small. From outer layer of small light cells the walls of the bubble are formed - trophoblast. Subsequently, trophoblast cells form the outer layer of the membranes of the embryo. Larger dark cells ( Blastomeres) form a cluster - embryoblast(embryonic nodule, embryonic rudiment), which is located medially from the trophoblast. From this accumulation of cells (embryoblast) the embryo and adjacent extra-embryonic structures (except the trophoblast) develop. A small amount of fluid accumulates between the surface layer (trophoblast) and the germinal nodule.

By the end of the 1st week of development (6-7th day of pregnancy) the embryo is implanted ( implanted) into the uterine mucosa. The surface cells of the embryo, forming a vesicle - trophoblast (from the Greek trоphe - nutrition, trophicus - trophic, nourishing), secrete an enzyme that loosens the surface layer of the uterine mucosa. The latter is already prepared for the implantation of the embryo into it. By the time of ovulation (the release of an egg from the ovary), the uterine mucosa becomes thicker (up to 8 mm). The uterine glands and blood vessels grow in it. Numerous outgrowths - villi - appear on the trophoblast, which increases the surface of its contact with the tissues of the uterine mucosa. The trophoblast turns into the nutritious membrane of the embryo, which is called the villous membrane, or chorion. At first, the chorion has villi on all sides, then these villi are retained only on the side facing the wall of the uterus. In this place, a new organ develops from the chorion and the adjacent mucous membrane of the uterus - placenta(children's place). The placenta is an organ that connects the mother’s body with the embryo and provides its nutrition.

Second week of embryo development- this is the stage when embryoblast cells are divided into two layers(two plates), from which two bubbles are formed. From outer layer cells adjacent to the trophoblast is formed ectoblastic (amniotic) vesicle filled with amniotic fluid. From inner layer cells of the germinal node of the embryoblast is formed endoblastic (yolk) vesicle. The anlage (“body”) of the embryo is located where the amniotic sac comes into contact with the yolk sac. During this period, the embryo is a two-layer shield, consisting of two germ layers: the outer - ectoderm (from the Greek ektos - outside, derma - skin) and the inner - endoderm (from the Greek ektos - inside). The ectoderm faces the amniotic sac, and the endoderm is adjacent to the yolk sac. At this stage, the surfaces of the embryo can be determined. The dorsal surface is adjacent to the amniotic sac, and the ventral surface is adjacent to the yolk sac. The trophoblast cavity around the amniotic and vitelline vesicles is loosely filled with strands of extraembryonic mesenchyme cells. By the end of the 2nd week, the length of the embryo is only 1.5 mm. During this period, the embryonic shield thickens in its posterior (caudal) part. Here, the axial organs (notochord, neural tube) subsequently begin to develop.

Rice. Formation of the embryo and embryonic membranes in the early stages of human development.A - 2-3 weeks. B - 4 weeks: 1 - amnion cavity, 2 - embryo body, 3 - yolk sac, 4 - trophoblast. B - 6th week. G - fetus 4-5 months: 1 - body of the embryo (fetus), 2 - amnion, 3 - yolk sac, 4 - chorion, 5 - umbilical cord.

Third week of embryo development- period of education three-layer shield. The cells of the outer, ectodermal layer of the embryonic shield are displaced towards its posterior end, resulting in the formation of a roller elongated in the direction of the axis of the embryo. This cellular cord is called primitive streak. In the head (front) part of the primitive streak, cells grow and multiply faster, resulting in the formation of a small elevation - primary nodule (Hensen's node). The primary streak determines the bilateral symmetry of the embryo body, i.e. its right and left sides. The location of the primary nodule indicates cranial (head) end of the embryo's body.

As a result of the rapid growth of the primitive streak and primary nodule, the cells of which grow laterally between the ectoderm and endoderm, forming the middle germ layer - mesoderm. The mesoderm cells located between the sheets of the scutellum are called intraembryonic mesoderm, and those that migrate beyond its boundaries are called extraembryonic mesoderm.

Part of the mesoderm cells within the primary nodule grows especially actively forward, forming head (chordal) process. This process penetrates between the outer and inner layers from the head to the tail end of the embryo and forms a cellular cord - the dorsal string ( chord). The head (cranial) part of the embryo grows faster than the tail (caudal), which, together with the region of the primary tubercle, seems to retreat back. At the end of the 3rd week anterior to the primary tubercle in the outer germ layer, a longitudinal strip of actively growing cells is distinguished - neural plate. This plate soon bends, forming a longitudinal groove - neural groove. As the groove deepens, its edges thicken, move closer and grow together, closing the neural groove in neural tube. Subsequently, the entire nervous system develops from the neural tube. The ectoderm closes over the formed neural tube and loses connection with it.

During the same period, from the posterior part of the internal (endodermal) layer of the embryonic shield, a finger-like outgrowth penetrates into the extra-embryonic mesenchyme (into the so-called amniotic leg). allantois, which does not perform certain functions in humans. Along the allantois, blood umbilical (placental) vessels grow from the embryo through the amniotic pedicle to the chorionic villi. A cord containing blood vessels that connects the embryo with the extraembryonic membranes (placenta) forms the abdominal stalk. Thus, by the end of the 3rd week, the human embryo looks like a three-layer shield. In the region of the outer germ layer the neural tube is visible, and deeper - the dorsal chord, i.e. the axial organs of the human embryo appear.

Fourth week of embryo development is the period when the embryo, which looks like a three-layer shield, begins to bend in the transverse and longitudinal directions. The embryonic shield becomes convex, and its edges are delimited from the amnion by a deep groove - trunk fold. The body of the embryo turns from a flat shield into a three-dimensional one; the exodermis covers the body of the embryo from all sides.

Endoderm, once inside the body of the embryo, curls up into a tube and forms an embryonic rudiment future guts. The narrow opening through which the embryonic intestine communicates with the yolk sac later turns into umbilical ring. From the endoderm they are formed epithelium and glands of the digestive tract and respiratory tract. The ectoderm forms the nervous system, the epidermis of the skin and its derivatives, the epithelial lining of the oral cavity, anal rectum, and vagina. The mesoderm gives rise to internal organs (except for endoderm derivatives), the cardiovascular system, organs of the musculoskeletal system (bones, joints, muscles), and the skin itself.

The embryonic (primary) gut is initially closed in front and behind. At the anterior and posterior ends of the body of the embryo, invaginations of the ectoderm appear - the oral fossa (future oral cavity) and the anal (anal) fossa. Between the cavity of the primary intestine and the oral fossa there is a two-layer (ectoderm and endoderm) anterior (oropharyngeal) plate (membrane), between the intestine and the anal fossa there is a cloacal (anal) plate (membrane), also two-layer. The anterior (oropharyngeal) membrane breaks through in the 4th week of development. At the 3rd month, the posterior (anal) membrane breaks through.

As a result of bending, the body of the embryo is surrounded by the contents of the amnion - amniotic fluid, which acts as a protective environment that protects the embryo from damage, primarily mechanical (concussion). The yolk sac lags in growth and in the 2nd month of intrauterine development it looks like a small sac, and then is completely reduced. The abdominal stalk lengthens, becomes relatively thin and later receives the name umbilical cord.

During the 4th week, the differentiation of its mesoderm, which began at the end of the 3rd week of embryo development, continues. The dorsal part of the mesoderm, located on the sides of the notochord, forms paired projections - somites. Somites are segmented, i.e. are divided into metamerically located areas. Therefore, the dorsal part of the mesoderm is called segmented. Segmentation of somites occurs gradually in the direction from front to back. On the 20th day, the 3rd pair of somites is formed, by the 30th day there are already 30 of them, and on the 35th day - 43-44 pairs.

Rice. Diagram of the location of the axial organs in the body of the embryo (cross section through the body).1 - neural tube; 2 - chord; 3 - aorta; 4 - sclerotome; 5 - myotome; 6 - dermatome; 7 - primary gut; 8 - primary body cavity (whole); 9 - somatopleura; 10 - splanchnopleura; 11 - ectoderm.

The ventral part of the mesoderm is not divided into segments, but is represented on each side by two plates (the unsegmented part of the mesoderm). The medial (visceral) plate is adjacent to the endoderm (primary gut) and is called the splanchnopleura; lateral (outer) - to the wall of the body of the embryo, to the ectoderm, and is called somatopleura (Fig.). From the splanchno- and somatopleura the epithelial cover of the serous membranes (mesothelium), as well as the lamina propria of the serous membranes and the subserosal base develop. The mesenchyme of the splanchnopleura also goes to the construction of all layers of the digestive tube, except for the epithelium and glands, which are formed from the endoderm. The endoderm gives rise to the glands of the esophagus, stomach, liver with bile ducts, glandular tissue of the pancreas, epithelial lining and glands of the respiratory organs. The space between the plates of the unsegmented part of the mesoderm turns into the body cavity of the embryo, which is divided into the abdominal, pleural and pericardial cavities.

The mesoderm at the border between the somites and the splanchnopleura forms nephrotomes (segmental legs), from which the tubules of the primary kidney develop. Three primordia are formed from the dorsal part of the mesoderm - somites. The ventromedial portion of the somites - the sclerotome - is used to build skeletogenic tissue, which gives rise to the bones and cartilages of the axial skeleton - the spine. Lateral to it lies the myotome, from which striated skeletal muscles develop. In the dorsolateral part of the somite there is a dermatome, from its tissue the connective tissue base of the skin is formed - the dermis.

At the 4th week, in the head section on each side of the embryo, the rudiments of the inner ear (first the auditory pits, then the auditory vesicles) and the future lens of the eye, which is located above the lateral protrusion of the brain - the optic vesicle, are formed from the ectoderm. At the same time, the visceral parts of the head are transformed, grouping around the oral bay in the form of the frontal and maxillary processes. Caudal to these processes, the contours of the mandibular and sublingual (hyoid) visceral arches are visible.

Rice. Human embryo – 7th week of development.

On the anterior surface of the embryo's body, the cardiac tubercles are distinguished, followed by the hepatic tubercles. The depression between these tubercles indicates the place of formation of the transverse septum - one of the rudiments of the diaphragm.

Caudal to the hepatic tubercle is the abdominal stalk, which includes large blood vessels and connects the embryo to the placenta (umbilical cord).

The period from the 5th to the 8th week of embryo development- period of development of organs (organogenesis) and tissues (histogenesis). This is the period of early development of the heart, lungs, complication of the structure of the intestinal tube, the formation of visceral and gill arches, and the formation of capsules of the sensory organs. The neural tube closes completely and expands in the cerebrum (the future brain). At the age of about 31-32 days (5th week, embryo length 7.5 cm), fin-like rudiments (buds) of the arms appear at the level of the lower cervical and 1st thoracic segments of the body. By the 40th day, the rudiments of the legs are formed (at the level of the lower lumbar and upper sacral segments).

At the 6th week, the buds of the outer ear are noticeable, from the end of the 6th-7th week - the fingers, and then the toes (Fig.).

By the end of the 7th week, the eyelids begin to form. Thanks to this, the eyes are outlined more clearly. At the 8th week, the formation of embryonic organs ends. From the 9th week, i.e. from the beginning of the third month, the embryo takes on the appearance of a person and is called a fetus.

Starting from the third month and throughout the entire fetal period, growth and further development of the formed organs and body parts occur. At the same time, differentiation of the external genitalia begins. The nails on the fingers are laid. From the end of the 5th month, eyebrows and eyelashes become noticeable. In the 7th month, the eyelids open and fat begins to accumulate in the subcutaneous tissue. In X month the fetus is born.

Related information.

A woman is created by nature in such a way that at least once in her life she can give the world a new person. The period of waiting and birth of a child is the brightest and at the same time alarming time. But the expectant mother should not worry unnecessarily. She should know that a normal pregnancy is the key to the proper development of her child.

If a woman has a clear idea of ​​how the baby’s body is formed throughout pregnancy, then it will be quite easy for her to do everything necessary to avoid the development of pathologies.

Should a woman know how her child is developing?

Knowing how intrauterine development of the fetus occurs week by week, the expectant mother can correctly organize her diet and daily routine. Also, having complete information about what changes are considered normal, a woman will avoid a state of unreasonable anxiety.

Calculating the intrauterine development of the fetus by week, it should be noted that it lasts 40 of these calendar periods. In other words, a woman’s pregnancy lasts 280 days. During this time, the child undergoes a complete process of formation and development of all organs and systems.

Gynecologists examine the intrauterine development of the fetus by week and by period, of which there are two: embryonic and fetal.

The first lasts from the moment the egg is fertilized until the 8th week of pregnancy. During this period, after fertilization, an embryo is formed, which descends into the cavity and attaches to it. The fetal period lasts from the beginning of the 9th week until the moment of birth. The embryo transforms into a fetus, develops and grows.

It is also common to divide pregnancy into trimesters:

• First trimester (1 - 12 weeks).
• Second trimester (13 - 27 weeks).
• Third trimester (28 - 40 weeks).

Now we can take a closer look at how intrauterine development of the fetus occurs week by week.

What happens during the embryonic period?

The most important thing from this period of development is the formation of the embryo. Over time, he begins to take on the shape of a person. The embryo is formed from the moment the egg is fertilized. This usually occurs in the fallopian tube.

From the moment the egg is fertilized, the development of the fetus begins.
According to the weeks of pregnancy, a morula is formed in the first seven days. It is a multicellular organism, a prototype of an embryo. The morula attaches to the wall of the uterus, and its outer cells form the umbilical cord and the outer membranes of the fetus. From the cells that are located inside it, the organs and tissues of the unborn child are formed.

How does the woman feel?

In the first week of pregnancy, a woman’s body temperature is slightly elevated, it is close to 37˚C. There are no hormonal changes in the body yet, but the expectant mother instinctively feels the changes taking place. From this moment on, a woman should be very careful about her diet and lifestyle, eliminate bad habits and follow the doctor’s recommendations.

Every expectant mother will be very interested in how the fetus develops over the weeks of pregnancy. This information will help a woman prevent many dangerous conditions. The third week of pregnancy is alarming because it is during this period that there is the greatest risk of fetal rejection. The woman's immune system tries to reject the embryo. However, in response, a special protein is released that suppresses this protective reaction, and the unborn child has a greater chance of survival.

What happens to the embryo in the first weeks of pregnancy?

This period is also characterized by the formation of the placenta. The unborn child at three weeks is a ball with a diameter of 0.2 mm. But during this period, the lungs and respiratory organs, cardiovascular system, spinal cord and brain are actively formed, and the baby’s face and gender are also formed.
The woman begins to feel mood swings, drowsiness and fatigue, and early toxicosis may occur.

Further development of the fetus (this is already the fourth week of pregnancy) occurs very intensively. The unborn child develops three germ layers:

• endoderm - the basis for the development of internal organs;
• mesoderm is what the skeleton and bones will be formed from;
• ectoderm - material for the formation of the nervous system.

The embryo already has a pulsating tube that develops into a heart. During this period, a heartbeat can be heard on an ultrasound. The respiratory organs and brain continue to form, and the face emerges more clearly. The embryo develops limbs, and by the end of the week they are already bending. The embryo is located in the placenta and maintains contact with the mother through this organ.

His heart is already beating!

During this period, many women are just learning about their pregnancy, especially if it is the first. Having found out this fact for herself, the expectant mother is interested in the main question: how does the fetus develop?

In terms of weeks of pregnancy, this is already the fifth calendar period. At this time, the embryo still bears little resemblance to a human being, but its heart already beats, its sex is clearly defined, and its kidneys, liver, pancreas and thyroid glands are formed.

Already at the 8th week, the future baby acquires the outlines of a person, his height is 3-4 cm. His arms and legs are already formed, his forehead is clearly visible, and the outlines of his eyes, lips and nose have been outlined. Internal organs are actively formed and developing. The stomach is already able to produce juice, the heart is formed, the intestines are growing, the trachea and bronchi have appeared. The spine, brain and limbs are actively developing.

By the end of the eighth week of pregnancy, the embryonic period of development ends, but the first trimester still continues. The unborn child has already acquired a human appearance, the placental-uterine blood circulation has been formed.

Fetal period

This stage begins from the 9th week of pregnancy and lasts until birth. The fetal period is divided into two parts:

• early (9 - 28 weeks);
• late (29 - 40 weeks).

During the early fetal stage, fetal development continues. In terms of weeks of pregnancy, this is the ninth. At this stage, fetal growth is 40-50 mm. He begins to show activity: bends his arms and legs, turns his head, brings his fingers to his mouth. But the mother is not yet able to feel this, the fetus is still too small.
Externally, the future baby looks like a little man with a big head. The eyes are still closed, and the skin is transparent. The genital organs begin to form, and this process will continue until the 20th week. The cerebellum and pituitary gland develop. The heart has four chambers. The tail disappears, being replaced by the tailbone.

The embryo turns into a fetus

At the tenth week of pregnancy, the embryo is already called a fetus and weighs 5 grams. His photographs already show isolated fingers, neck, elbows, knees, eyelids and upper lip.

There are taste buds on the tongue, the thickness of the umbilical cord increases.

The eleventh week of pregnancy is characterized by further development of the fetus. He already has eyelashes and baby teeth. The rectum is formed. The spinal cord is already producing red blood cells. The intestines are ready to go.

During this period, many mothers are referred by a gynecologist for a routine ultrasound. When undergoing this procedure, women are interested in the main question: is fetal development normal?

According to the weeks of pregnancy, the twelfth period begins. During this period, the child’s phalanges of fingers and earlobes are formed, he opens and closes his eyes. The intestines are already contracting, and the liver is able to secrete bile. The baby’s circulatory system is functioning, leukocytes appear.

At the twelfth week, the first trimester of pregnancy ends and the second begins.

The baby is actively growing

During this period, all fetal systems are formed, their development and growth are underway. At the thirteenth week, which marks the beginning of the second trimester, the baby reaches up to 80 mm in length and weighs about 20 g. At this time, the skeleton of the fetus is intensively formed, the pancreas begins to produce insulin.

The gynecologist will refer the expectant mother for the first genetic test. After studying the results of the ultrasound, the doctor will be able to tell you how the intrauterine development of the fetus occurs by week of pregnancy, and whether the indicators correspond to the norm.

At the 14th week, the baby’s face continues to form, facial expressions, eyebrows and hair appear on the head. On the body of the fetus, fluff and cheese-like lubricant are formed. The thyroid gland begins to work and its own hormonal levels develop.
The excretory system is functioning, the child is making breathing movements.

In the antenatal clinic, you probably saw a stand that depicted the intrauterine development of the fetus by week.

A table with this kind of information will be useful to every woman.

At the fifteenth week of pregnancy, the child develops hearing, the intestines form original feces, and the placenta thickens. The fruit weighs about 50 g, its height is 60 mm.

The expectant mother feels the baby's first movements

The sixteenth week of pregnancy is marked by an increase in the volume of amniotic fluid. The baby is actively moving, and the mother begins to feel it. The muscles on the face are developed and the child at this stage is characterized by facial expressions. The bones and nails are almost completely formed, the skin is very thin and the blood vessels are clearly visible through it.

During this period, the gynecologist refers the woman to a second genetic screening. To do this, the expectant mother will have to undergo a second ultrasound. It clearly shows the intrauterine development of the fetus week by week. Photos that can be taken at this stage are presented below.

We count fetal movements

The third trimester begins from the 28th week of pregnancy, and the late fetal period begins from the 29th week. At this time, the baby is a little cramped in the womb, and his movements are not so active. Nevertheless, the woman must clearly monitor the tremors, their number should be at least 10 per hour. The brain is actively developing, and furrows appear on it. The teeth are covered with enamel, the eyes are capable of focusing. The baby's weight is about 1250 g and height is 37 cm.

At 30 - 31 weeks of pregnancy, the baby already takes its final position in the uterus. The fetus actively gains weight by increasing muscle mass and subcutaneous fat. If a child is born during this period, he has every chance of survival.

Further intrauterine development of the child (week by week this is already the 32nd calendar period) is characterized by the improvement of the immune and nervous systems. The child has his own waking and sleeping schedule, he has his own temperament. The baby weighs 1800 g and is 42 cm tall.

At the 33rd - 34th week of pregnancy, the baby actively trains the lungs and perceives the entire environment to the fullest. The skin of the fetus becomes smooth, the bones of the skull become stronger.

Baby getting ready for birth

At 36 - 37 weeks of pregnancy, the fetus is preparing to be born. He’s already cramped in his mother’s belly and it’s becoming more and more difficult for him to move.

His body has enough fat reserves for thermoregulation after birth, his lungs are ready to breathe. There is no longer any fuzz on the body, but the hair on the head and nails are growing back.

At 38 - 40 weeks, all mothers expect childbirth. This can happen at any time. The child lowers and the mother begins to breathe easier. The woman carefully monitors the passage of the mucus plug and the appearance of contractions.

And finally, it happened! Mom and baby are now together. The baby is still very small, but full of strength to explore the new world. Now his status is a newborn.

Table of intrauterine development of the fetus by week of pregnancy

This article provides a full description of how the intrauterine development of a child occurs week by week. The table below will serve as a kind of conclusion to all of the above and will serve as a reminder for the expectant mother.

Intrauterine development of the fetus by week of pregnancy

Gestational age in weeks	Fruit length, cm	Fruit weight, g	Development of organs and systems
4	0,1		Fertilization of the egg, its implantation, embryo and organ rudiments.
5	0,15 - 0,2		Layer of the liver, pancreas, upper respiratory organs, heart.
6	0,4 - 0,6		The appearance of limb buds, hearing the heartbeat, the neural tube closes, and parts of the larynx and middle ear are formed.
7	0,7 - 0,9		The trachea, esophagus, small intestine, adrenal glands and sternum develop. The brain is actively developing.
8	0,9 - 1,2		The embryo has a clearly distinguishable body and head, which are equal in size. The rudiments of the nose, eyes, mouth and reproductive organs are formed.
9	1,3 - 1,5	1	The cerebellum develops, fingers on the limbs form.
10 - 11	2,7 - 3,5	4	Joints, upper lip, ears, external genitalia, and the beginnings of baby teeth develop.
12	9	20 - 25	The face is formed, the intestines contract, the liver produces bile, the child moves.
13	10	28	The limbs are fully formed. The pancreas produces insulin.
14 - 15	12,5	50 - 90	The excretory system is active, the child produces urine.
16	16	120	Let's distinguish the sex of the fetus. The skin is very thin, muscles are forming. The child does not move so chaotically, the mother feels the first tremors.
20	25	280 - 300	There is fluff and cheese-like lubricant on the baby's skin. The intestines form original feces. The child is able to hear.
24	30	600 - 800	The work of the kidneys is activated, the fetus dynamically gains weight.
28	35	1200	The muscles and reproductive system of the child are formed.
32	40	1500 - 1600	The sensory organs and nervous system are actively developing: the baby is able to see light and feel taste.
36	45	2400 - 2500	The child quickly gains weight and his activity decreases.
40	50-52	3200 - 3500	The baby is ready to be born.

Of course, it is best to study this information when you are just planning a pregnancy. Then a woman has a better chance of properly organizing her diet, regimen, and taking the necessary vitamins and minerals. However, information about the intrauterine development of the baby will always be timely and interesting for the expectant mother, regardless of the duration of her pregnancy.