The emergence of the human embryo. At what stage does the embryo become a person? Factors influencing embryo development

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 the 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 are actively formed, the cardiovascular system, spinal cord and brain, as well as the face and gender of the baby.
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. Actively formed and developed internal organs. 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, its own hormonal background.
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.

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.

A fetus (synonymous with an embryo) is an organism that develops inside the egg shells or in the mother's body. Embryonic, or embryonic, development in humans is understood as the early period of development of the body (up to 8 weeks), during which a body is formed from a fertilized egg that has the basic morphological characteristics of a person. After 8 weeks, the developing human body is called a fetus (see).

Embryonic development divided into a number of periods.
1. The period of a one-cell embryo, or zygote, is short-term, occurring from the moment of fertilization until the beginning of egg fragmentation.

2. Crushing period. During this period, cells occur. The resulting cells are called blastomeres. First, a bunch of blastomeres is formed, resembling a raspberry in shape - a morula, then a spherical single-layer blastula; the wall of the blastula is the blastoderm, the cavity is the blastocele.

3. Gastrulation. A single-layer embryo turns into a two-layer one - a gastrula, consisting of an outer germ layer - ectoderm and an inner one - endoderm. In vertebrates, already during gastrulation, the third germ layer, the mesoderm, appears. During evolution in chordates, the process of gastrulation became more complicated with the emergence of an axial complex of primordia (the anlage of the nervous system, axial and musculature) on the dorsal side of the embryo.

4. The period of separation of the main rudiments of organs and tissues and their further development. Simultaneously with these processes, the unification of parts into a single developing whole is intensified. The skin, the nervous system, and partly from the endoderm - the epithelium of the digestive canal and its glands are formed from the ectoderm; from mesoderm - muscles, epithelium genitourinary system and serous membranes, from mesenchyme - connective, cartilaginous and bone tissue, vascular system and blood.

When conditions change, the course of development of individual parts of the embryo may change and the germ layers may give rise to organs and tissues that should not develop from them under normal conditions. Factors that change development conditions may be environment(its chemistry, temperature, etc.), interaction between parts (cells, rudiments) of the embryo itself, as well as heredity. All these factors are closely interconnected.

Rice. 1. Scheme of the early stages of development of the human embryo: a - stage of the inner cell mass; b - eight-day embryo; c - twelve-day embryo; d - thirteen, - fourteen day embryo. 1 - trophoblast; 2 - blastocele; 3 - amnion cavity; 4 - endoderm cells; 5 - amnion; 6 - embryo; 7 - yolk sac; 8 - mesoderm cells; 9 - stalk; 10 - chorionic villus; 11 - extraembryonic coelom.

Rice. 2. The embryo and its membranes in the early stages of development (a - c - successive stages): 1 - chorion; 2 - allantois; 3 - yolk sac; 4- amnion; 5 - extraembryonic coelom; 6 - umbilical cord; 7 - umbilical vessels; 8 - amnion cavity.

Rice. 3. Human embryo: a - by the end of the 4th week; b - by the end of the 5th week; c - by the end of the 7th week after fertilization.

In humans, fertilization occurs in the oviduct. The crushing process takes place within 3-4 days, when the embryo moves along the fallopian tube to the uterus. As a result of fragmentation, a shell is formed from the surface blastomeres, which participates in the nutrition of the embryo - the trophoblast. The central blastomeres form the embryoblast, from which the body of the embryo develops. For 4-6 days the embryo is in the uterine cavity. With the beginning of the second week, the embryo immerses into the wall of the uterus (implantation). In a 7.5-day-old embryo, an amniotic sac forms, the part of which facing the endoderm is the ectoderm of the embryo. During this period, the embryo has the shape of a shield (disc). From it, cells of extraembryonic mesenchyme migrate into the cavity of the blastocyst and fill it (Fig. 1). Together with the trophoblast, it forms the villous membrane of the embryo - the chorion (see). By the end of the second week, a yolk vesicle forms. As a result of mesenchyme overgrowing the amniotic and yolk sacs, the amnion and yolk sac are formed.

"Extraembryonic" parts play an important role in the development of the embryo. The yolk sac in the human embryo functions only in the early stages of development, participating in the nutrition of the embryo and performing a hematopoietic function. In oviparous higher vertebrates, the allantois acts as a urinary sac; in humans, it is a finger-like outgrowth of the hindgut, along which it grows to the chorion. The amnion - a water membrane - forms a closed sac around the embryo, filled with liquid - amniotic fluid. It protects the embryo from harmful influences and creates favorable conditions for its development (Fig. 2).

At the 3rd week of development, a dense cord of growing cells stands out on the dorsal side of the embryo - the primary streak, the head section of which thickens and forms the primary (Hensen's) node. The cells of the primitive streak are immersed in the primary groove, penetrate into the space between the ectoderm and endoderm and give rise to the middle germ layer. In the 3rd week, the dorsal chord and neural tube are formed.

At the 4th week, the embryo separates from the extra-embryonic parts and, as a result of increased growth, curls into a tube. At the same time, the mesoderm differentiates and body segments - somites - are formed (Fig. 3, a). In parallel with segmentation, the initial processes of organogenesis (see) and histogenesis occur. At the 5th week, the rudiments of the arms and then the legs appear, on the 6th they are divided into main sections, and on the 7th the rudiments of the fingers appear (Fig. 3, b and 3, c). At the age of 8 weeks, the embryo acquires the basic morphological characteristics of a person in appearance and internal organization. Its length (from the crown to the coccyx) is 4 cm, weight is 4-5 g. By the end of the 8th week, the laying of the embryonic organs ends.

Every woman who dreams of adding to her family, seeing the long-awaited two lines on the test, becomes indescribably delighted. Literally from the first days of pregnancy, she begins to show concern for the unborn baby: she refuses bad habits, follows a diet, reduces physical exercise. However, not all ladies delve into the intricacies of the development of a tiny organism, limiting themselves to only studying ultrasound images. Meanwhile, while in the womb, the embryo goes through a long journey before turning into a full-fledged little person. In this article we will look at the difference between a fetus and an embryo.

Definitions

Fetus- developing in the mother's womb human body after the laying of the main systems and organs. This term is used exclusively in relation to an unborn child. The period of development of the body under consideration is called fetal and begins when it reaches 8-9 weeks of age. This stage is characterized by intensive growth, tissue differentiation, development of organs and systems, and the completion of the formation of the fetal membranes and placenta. A 38-week baby is considered fully term. At this point, the fetus acquires signs of maturity: length from 47 cm, weight from 2500 g, convex breasts, pale pink skin without wrinkles, etc. Babies born between 28 and 37 weeks are considered premature, but at the same time quite viable. They require very careful care and are sometimes under the supervision of doctors for a long time. The most effective method Ultrasound examination is recognized for fetal diagnostics.

Embryo– a human embryo at the initial stage of its development until it emerges from the membranes. During this stage, a body with certain morphological characteristics is formed from the egg. This period lasts 8 weeks, after which the embryo is usually called a fetus. The embryo results from the fusion of the nuclei of the egg with the sperm. At the end of the third week of development, the embryo develops a head and a primitive heart, and after a few more days it begins to pump blood throughout the body and placenta. During the formation of the embryo, limbs and eyes, ears and the beginnings of teeth are formed, the tail gradually decreases, and then completely disappears. By the end of the eighth week, the process of laying the main vital organs is almost complete.

Comparison

Both of these terms refer to a growing organism at different stages of development. An embryo is a fetus from the moment of conception until the 8th week of pregnancy. A microscopic body appears in the fertilized egg, which is an oval or round formation several millimeters in size. The yolk sac inside provides nutrition to the embryo. The fertilized egg increases in size along with the embryo. On initial stage formation, the embryo bears little resemblance to a human. It looks like a tiny crooked “worm” with a tail and no clearly defined head. Closer to 8-9 weeks, the embryo develops limbs, eyes, the heart begins to beat, and other vital organs are formed. The head becomes visible, but disproportionately large in relation to the body. Maximum size the embryo reaches only 3-4 cm, and weighs about 5 g.

The main difference between a fetus and an embryo is the intrauterine age of development. As mentioned above, the embryo is the organism that forms during the first eight weeks. Upon reaching this age, the embryo begins to be called a fetus. From now on, its nutrition is provided not by the yolk sac, but by the placenta, an organ located inside the uterus that communicates between the mother and the unborn baby. As he develops, he becomes more and more human-like. The body lengthens and acquires normal proportions, the limbs increase in size, the ears take their place on the sides of the head, etc. The fetus is actively growing and gaining weight. The weight of a full-term toddler is at least 2.5 kg, and the height is 47 cm.

Let's summarize what is the difference between a fetus and an embryo.

A person is born when a sperm, a male reproductive cell, enters a woman’s body, merges with her egg and forms a single cell. A new cell develops by division. At some time, the embryo appears and then disappears the signs inherent in representatives of the animal world: gill arches are formed in the image and likeness of fish, the jaw joint that reptiles have, a tail and thin hair grow. These ancient forms do not exist for long and then either change or disappear.

Germ It seems to quickly pass through all stages of evolution. This process is called recapitulation(repetition).

German biologists Fritz Müller and Ernst Haeckel formulated in the 19th century. biogenetic law: “The individual development of each individual is a short and rapid repetition historical development the species to which this individual belongs."

Developing in the mother's womb, the human embryo goes through the entire evolution of the living. This four-week-old embryo (its length is only 4 mm) has clearly visible gill apparatus, like a fish, and a tail. They will disappear in a few weeks. Russian biologist A.N. Severtsov (1866 - 1936) established that in individual development The characteristics of not adult ancestors are repeated, but their embryos.

A child develops in the mother's womb for approximately 266 days, or 38 weeks (the first eight weeks are called an embryo, then a fetus). During the embryonic period, an embryo gradually forms from a shapeless accumulation of cells, which in general terms already resembles a human being. By the end of these eight weeks, all the main internal and external human organs have been formed. True, according to appearance The sex of the embryo cannot yet be determined - this will only be possible after another two weeks.

At the ninth week, the fertile, or fetal, period begins - the time of growth and maturation of the body. From this time on, the tiny child, lying in a special water shell, begins to bend and move his arms and legs. His skin, initially transparent as glass, becomes cloudy and loses its transparency. By the end of the fourth month, the baby's heart becomes noticeably stronger. Every day it pumps more than 30 liters of blood through its blood vessels. Now the fruit reaches 16 cm in length and weighs 170 g. In the fifth month unborn child He is already quite noticeably pushing, dangling his arms and legs. He already feels and hears movement. Loud noises make his heart beat faster. And here’s something else that happens at this time: a pattern of thin twisted lines appears on the fingertips. This pattern “sticks” to your fingers forever. Having touched any object, a person leaves his fingerprints on it. They are unique: you won’t find two people on Earth with the same fingerprints.

By the beginning of the sixth month, the fetus weighs 600 g. If the baby is born in the sixth month of pregnancy (i.e. ahead of schedule), then - with good care from doctors - he will survive. And if everything goes well, he will be born at the end of the ninth month. Such newborns weigh at least 3200 g, with an average height of 50 cm.

The development of an embryo week by week is a lifelong journey. Only 300 days separate a tiny egg from becoming a newborn baby, a full-fledged person in whom all organs and systems are formed. Every mother wants to know more about what is happening in her tummy now, but the development process there does not stop day or night. No subsequent stage of development is as stormy and rich in transformations as the perinatal stage. Today we want to take a closer look at the development of the embryo week by week, so that you can have a good idea of ​​the complex path your baby goes through even before birth.

The beginning of the way

Often the expectant mother at this stage does not yet know that she is pregnant, but amazing events are already happening inside her. Pregnancy begins with fertilization, when the egg fuses with the sperm. Only a few hours will pass, and the cell will already begin to divide and descend into the uterus in order to be implanted there and remain for the next 9 months. We will begin to consider the process of embryo development week by week a little later, but for now the egg has approximately 5 days for its journey to the uterine cavity. After seven days, it is no longer a cell, but a multicellular organism that is implanted into the endometrium of the uterus, and the first transformations begin.

The embryo is in its 2nd week of development, now it is securely attached to the wall of the uterus, due to which its nutrition and development will occur in the next 9 months. The most important event of this week is the formation of the neural tube. This is the rudiment of the brain and spinal cord.

We continue to look at the development of the embryo week by week. The third week begins. It is at this time that a wide plate is formed - this is the baby’s brain, and at 21 weeks the tiny heart begins to beat. This brings us to the fourth week, which concludes the first month. Now the baby develops the rudiments of all the main internal organs: lungs and liver, intestines. It is the 4th week of embryo development that is characterized by the formation and development of the spine.

Second month

The first important stage is ending. Most often, a woman already realizes that she is pregnant, but sometimes this is still hidden even from the expectant mother. These are very important days on which the further development of the embryo depends. The first weeks are decisive in many ways, so if you are planning to become parents, you need to monitor your diet and lifestyle. The embryo is still very small, its length is only 4 mm, but very important processes take place inside this tiny organism. In the fifth week, sensory organs are formed. Think about this if you are planning to terminate your pregnancy. The foundations of the gastrointestinal tract and circulatory system are laid. The formation of the little man's face has already begun.

6th week of embryo development

Another important milestone in your baby's development. By the end of this week, the division of the heart into chambers will be completed. It’s only the second month of pregnancy, and the atria and ventricles are already forming. The digestive system is also improving, the liver and pancreas are already fully formed and are completing their development.

In addition, the brain is now actively forming and developing. At this time, it is very important to eat properly so that the baby’s body does not lack microelements. Facial muscles are actively developing. The upper limbs change, they become similar to those that we are used to seeing in newborns.

From the seventh to the eighth week

Now the expectant mother is already interested in what is happening in her tummy, and the best reference is a table of embryo development by week. It is especially interesting to study each week only the information that relates to the current stage. This way you go the whole way with your baby.

In the seventh week, the formation of the umbilical cord is completed. Now until birth, the baby will receive nutrition from her. Now the little man has grown up, he is already 15 mm in length, he can open his mouth and even make the first movements with his hands. The eyes and fingers are formed, the brain is growing and developing rapidly. By the beginning of the eighth week, the fetus begins to straighten. The baby’s face becomes completely human, the nose and eyes, ears and lips are already formed. What previously connected us with distant ancestors, namely the membrane between the fingers, is already lost at this stage of development.

Third month

Another important milestone is the development of the embryo at 9 weeks of pregnancy. At this stage, the fetus is actively growing and gaining strength. The mass is rapidly increasing, and soon he will become quite similar to a small person. Now the baby is actively learning to clench his fingers and make various movements. Another important point characterizing the development of the embryo (9 weeks) is the formation of the endocrine system. The endocrine glands begin to produce their secretions, and the body now produces norepinephrine and adrenaline. The baby may already experience various emotions.

Continuing to look at the development of the human embryo week by week, we smoothly move on to week 10. The embryo is in a fairly free position in the uterus, right now it has a sucking reflex. Despite the fact that the baby is still very small, he can not only make chaotic movements, but also consciously react to external stimuli. He turns his head, moves his fingers and pushes to the side. Therefore, now you can and should communicate with your baby.

The eleventh week is coming. Considering the development of the embryo by week of pregnancy, we cannot help but note this stage, because the placenta has reached its full development and independently provides nutrients and oxygen, removes metabolic products and carbon dioxide. At this time, the child’s eyes quickly change, an iris appears, which is responsible for their color, although even after birth they will be blue for some time, like all babies.

The twelfth week will please the mother with one more event: now the first breathing movements appear. Rib cage begins to prepare for implementation respiratory function, while in aquatic environment. The digestive and nervous system, the development of the reproductive system according to the female or male type is now clearly visible.

Fourth month

The first trimester of pregnancy has come to an end, the most difficult and dangerous, since most miscarriages occur at this moment. During the first three months, all vital organs and systems were laid down; now they will only grow and develop. And we will continue to look at the stages of embryo development week by week, so that you can get information about what happens to the baby at later stages. Now not yet full force, but still everything starts working digestive system. Even the intestines, in which the production of original feces, which is commonly called meconium, is included in the work. Your baby has already grown significantly, his length is about 11 cm, and his weight is only 28 g.

Fourteenth and fifteenth weeks

All stages of the development of a human embryo week by week are very important, since the baby in a short time goes from one cell to a complex organism, and all this miracle happens in just 9 months. These two weeks are characterized by the continuation of the development of all organs and systems that are already fully formed. Now not only the kidneys, but also the entire excretory system are involved in the work. The baby begins to produce urine and pee. Now the changes that the brain undergoes are clearly visible. The formation of hemispheres, convolutions and furrows continues. It is at week 15 that the baby’s endocrine system begins to produce hormones for the first time. The thymus gland and adrenal glands are directly involved in this process.

Embryo 16 weeks: fetal development

The fourth month of pregnancy ends. First-time mothers will soon feel their baby moving for the first time. A smile appears more and more often on a small face, hair, eyebrows and eyelashes begin to form. The external genitalia are now fully formed. It is at this stage that the ultrasound specialist will be able to reliably tell you who you are expecting: a boy or a girl. However, it happens that the child turns away or covers himself with his hands. Then you will have to wait to determine gender until the next screening.

Fifth month

Now you can rest assured that your baby hears and understands absolutely everything that happens around him. With various sharp sounds, he begins to actively move, so you can slowly open up the world of music and sounds for him. Spend more time in the forest, in nature, and turn on classical music. The fruit changes its position to vertical. The heartbeat becomes clear, and a woman can already determine how her baby’s heart is beating without a stethoscope.

Continuing to consider the stages of embryo development week by week, we move on to the eighteenth. The woman still lives in her usual rhythm, goes to work, but the growth of her baby does not stop for a minute. It is at this time that the pancreas and thyroid glands, as well as the pituitary gland, begin to work. The coordination of the baby’s movements also continues to improve; he is already dexterous enough to push off from the walls, but at the same time, his body size still allows him to travel in the womb. Every day the woman feels these movements more and more clearly, which gives the expectant mother a lot of joy.

The nineteenth week is the period when the baby begins to express his own attitude to the world, he smiles or squints with pleasure, and if he is dissatisfied or offended with something, he curls his lips. Now the baby feels your mood more than ever, so if the mother is upset or excited about something, this will definitely affect the baby’s mood. In addition, the vestibular apparatus begins to form, which is responsible for the position of the body in space.

The twentieth week ends the fifth month. You have already passed more than half of the journey, the golden stage of pregnancy is ahead. Toxicosis and fear for the child’s life are already behind us; at this stage, miscarriages occur much less frequently. The baby begins to play with his mother, constantly reminding him of his presence with active movements. But at the same time, his body weight is not too large, and his mother does not yet experience serious discomfort.

Sixth month

Considering the stages of embryo development week by week, it is necessary to note further important events. Let's see what happens to the baby in the sixth month. By 21 weeks, his weight is already about 300 g, and his height has reached half the length of the newborn’s body - 25 cm. The doctor calmly listens to his heartbeat. Now the child spends more time in a state of wakefulness. By week 22, the cardiovascular and respiratory systems, as well as breathing and swallowing reflexes, become much more advanced. The baby constantly swallows amniotic fluid and increases the frequency of respiratory movements.

By the beginning of the 23rd week, the sensory organs complete their formation. The child already sees well, he reacts to bright light, squints if the sun or a lamp shines on the woman’s stomach. Loud noises frighten the baby, so it is better to avoid noisy ones public places. During this period, the emotional connection with the mother becomes closer, the child experiences all the emotions that a woman experiences. The baby sleeps approximately 16 hours a day, but the period of his wakefulness will not go unnoticed by the mother.

Seventh month

Now if the baby is born, it will be quite viable, albeit premature. However, normally pregnancy runs its course, and we will continue to look at the development of the human embryo week by week. At week 25, the baby continues to grow, body weight increases and the layer of subcutaneous fat grows. Important Processes occur in the lungs: lung tissue appears here and the production of a special substance, surfactant, begins. The lungs are ready to begin their gas exchange functions.

The 26th week is approaching, the baby has already taken on the appearance familiar to a newborn. Now is the time for active growth muscle tissue, while the bones are strengthened and the rudiments of teeth are formed. In addition, another important event occurs this week: the world of smells opens up to the child.

The twenty-seventh week becomes the final week for the formation of individual metabolism. The body can now regulate body temperature. Already at week 28, functional asymmetry of the brain is established, that is, if the leader becomes left hemisphere, then the child will be born right-handed, and vice versa.

Eighth month

At week 29, the baby is already so consciously performing various movements that he can not only suck a finger, but also scratch behind the ear, stick out his tongue or smile. It is very interesting to observe him using a modern ultrasound machine. The brain and metabolism continue to actively develop. At week 30, the circulatory system improves, and the immune system begins to work. It is thanks to this that antibodies are produced in the blood, which will help protect the body from a variety of infections. The child's height at this stage is approximately 36 cm and weight is about 1.2 kg.

At week 31, the child’s functioning of all organs and systems improves, and the brain and metabolism continue to actively develop. The endocrine system actively produces hormones; they regulate metabolism, as well as the baby’s sleep and wakefulness patterns. In addition, a special hormone begins to enter the mother's blood, which stimulates the production of estrogen. It is thanks to him that the mammary glands begin to prepare for milk production. Finally, at 32 weeks the baby turns head down. It will remain in this position until the end of pregnancy.

Ninth month: from 33 to 36 weeks

No matter when your baby is born, he is completely ready to function independently. At week 33, the brain completes its formation, all internal organs work as a harmonious organism. At this time, the skin becomes light, and the nails have almost acquired a normal appearance. The baby's lungs are fully formed, and at the beginning premature birth it will not be much different from children born at 37 weeks.

At 34 weeks, the baby's hair begins to grow rapidly. The bones of the skeleton are also strengthened, which is why mom needs more calcium. By the beginning of the 35th week, the embryo has already reached a height of 42-46 cm, and its weight is about 2500 kg. The liver begins intensive work, it accumulates iron reserves. By the 36th week, the baby takes a position in the uterus that ensures maximum free passage through the birth canal. The head is bent, the limbs are compressed - this position is due to nature, so the baby accepts it, obeying the biological clock. The bones of the skull become soft. This is necessary for normal childbirth. But all the other bones are already fully formed. By the end of the week, intrauterine development is completely completed, and now the embryo is ready to be born at any moment.

From 37 to 42 weeks

Things for the maternity hospital should already be collected, since the baby can be born at any moment. Now the child is only accumulating subcutaneous fat, becoming more and more like those plump babies they like to show in videos. Doctors believe that birth on any day during these five weeks is normal. Only if the period exceeds 42 weeks will doctors resort to drugs that induce labor. For the expectant mother You need to rest as much as possible, as difficult times will soon come. At this time, the baby moves quite little, there is not enough space for him, and the position is not conducive to activity. As soon as the uterus begins to contract, painful sensations appear, you need to go to the hospital, where doctors will provide the necessary assistance.

So, we looked at the main stages of human embryo development week by week. We hope this material will give you the necessary information about your future baby.