Development Of An Embryo - From Week To Week

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Development Of An Embryo - From Week To Week
Development Of An Embryo - From Week To Week
Video: Development Of An Embryo - From Week To Week
Video: Fetal Development Week by Week Overview 2023, February
Anonim

This is how an unborn child develops

It takes around nine months to develop from a microscopic germ cell to a mature child. A period in which all vital organs and tissues are formed. Here you will find a description of important developmental steps for each week of pregnancy - from the fertilization of the egg cell, the development of the first organs of the embryo and the steady growth to the birth of the child.

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  • How are pregnancy weeks counted?
  • What happens from the first to the fourth week of pregnancy (1st month)?
  • What happens in the fifth and sixth week of pregnancy (2nd month)?
  • What happens in the seventh and eighth week of pregnancy (2nd month)?
  • What happens in the ninth and tenth week of pregnancy (3rd month)?
  • What happens in the eleventh and twelfth week of pregnancy (3rd month)?
  • What happens from the 13th to the 16th week of pregnancy (4th month)?
  • What happens from the 17th to the 20th week of pregnancy (5th month)?
  • What happens from the 21st to the 24th week of pregnancy (6th month)?
  • What happens from the 25th to the 28th week of pregnancy (7th month)?
  • What happens from the 29th to the 32nd week of pregnancy (8th month)?
  • What happens from the 33rd week of pregnancy to the birth?

How are pregnancy weeks counted?

A normal pregnancy lasts a total of 40 weeks or 280 days. The first day of the last menstrual bleeding is used as the start of pregnancy. However, ovulation and fertilization do not take place until around two weeks after this day, which means that, strictly speaking, there is no pregnancy in the first two weeks of pregnancy. Nevertheless, this counting method has proven itself, since most women know the exact date of their last menstrual bleeding, but the exact time of fertilization cannot be clearly determined. More on the topic: How does fertilization occur?

Calculate the due date

Based on the first day of the last menstrual bleeding, the expected due date can also be calculated. The formula for this is called Naegele's rule:

Day of the last menstruation + 7 days - 3 months + 1 year = due date

Note Only very few children are born on the exact date calculated, a deviation of a few days is quite normal. In addition, the child's growth and development are regularly monitored using ultrasound and included in the determination of the gestational age.

What happens from the first to the fourth week of pregnancy (1st month)?

Ovulation occurs around the middle of a woman's monthly cycle. The expelled mature egg is absorbed by the fallopian tube and can be fertilized for around 24 hours. If a fusion with a sperm cell (fertilization) occurs during this period, a new organism is created. This is initially called a zygote. By combining the genetic information of the mother's egg cell and the father's sperm cell, the blueprint for the new life is complete and a new person can develop. More on the topic: A pregnancy begins

Shortly after fertilization, the zygote begins to divide several times and to migrate towards the uterus with the help of rhythmic contractions of the fallopian tube. About six days after fertilization, it nests there (nidation, implantation). Some women experience slight vaginal bleeding, known as implantation bleeding. Once implantation has taken place, the next menstrual period will not occur.

At the time of implantation, several cell nuclei and cell layers have already formed, from which the individual organs and tissues will later develop. One speaks now of a blastocyst. Towards the end of the fourth week of pregnancy, the cells begin to specialize: some develop into the approximately two millimeter large germinal disc, from which the actual embryo later develops, while others develop into the placenta (placenta).

The first amniotic fluid also begins to form; at the end of the fourth week of pregnancy, the embryo is completely surrounded by it. It protects it from dehydration and injuries, ensures its good mobility and also has immunological functions. By the last trimester of pregnancy, the amount of amniotic fluid will increase to up to 1,000 ml; physiologically, it will decrease somewhat before birth.

What happens in the fifth and sixth week of pregnancy (2nd month)?

The hormonal changes in the woman's body have long since begun. It forms the basis for the requirements for pregnancy to be created and for the embryo to develop correctly. Some women are already noticing early signs of pregnancy. These include a lack of menstrual bleeding, a tearing feeling in the breasts, fatigue, frequent urination and slight pelvic pain.

The germinal disc continues to develop and now consists of three layers, from which all the organ systems and tissues of the body are created later in countless further division steps.

During the sixth week of pregnancy, the first organs begin to take shape, and the head, trunk and attachments of the limbs can also be seen. This week represents a milestone in the development of the embryo: the heart begins to beat and the embryo develops its own circulatory system. The embryo is now around five millimeters in size.

What happens in the seventh and eighth week of pregnancy (2nd month)?

By the eighth week of pregnancy, the embryo is around 15 millimeters in size. In addition to the heart, other organs such as the kidneys and stomach are created and begin to work. With the mouth, nose and eyes, the sense organs now also begin to develop. The head and upper extremities dominate the body shape of the embryo. First movements of arms and legs can be seen.

In early pregnancy, the embryo is supplied with nutrients via the yolk sac. The placenta continues to develop and the umbilical cord can now also be recognized. By the end of pregnancy, it will be 50 cm long and an inch or two thick.

What happens in the ninth and tenth week of pregnancy (3rd month)?

Nerve cells and muscles are so well developed that the embryo can move around in an unspecified manner. However, the mother cannot yet feel these movements. The embryo's body measures around 25 millimeters from head to rump and weighs around 15 grams.

The fingers are now clearly visible on the hands. The elbows, feet and toes have also started to develop. Facial features such as ears, nose, mouth and eyes take on more and more shape. The eyes of the embryo are still permanently open at this point, the eyelids only develop completely later. The head is getting rounder.

What happens in the eleventh and twelfth week of pregnancy (3rd month)?

The unborn child is no longer called an embryo, the so-called fetal period has begun. The nerve tracts have become more networked so that the embryo's movements can be more and more targeted; it can now make a fist, for example. The nervous system develops extremely quickly, every day countless new nerve cords and connections are formed.

The systems for all organ systems have already been set up, and they will increasingly mature in the coming weeks and months. The head is still the largest part of the fetus, making up about half the total height. The systems for the milk teeth are already in place in the jaw. The external sexual characteristics of the fetus will become visible, but they cannot yet be seen on the ultrasound image.

In the twelfth week of pregnancy, the placenta takes on the task of supplying the approximately five centimeter embryo with oxygen and nutrients from the mother's blood. The yolk sac recedes.

What happens from the 13th to the 16th week of pregnancy (4th month)?

The eyelids have formed and the fetus's eyes are now closed. The soft cartilage of the skeletal structure begins to ossify. The skin is almost completely developed. So-called lanugo hair forms, which only slowly regresses around the due date. The lanugo hairs together with the so-called cheese smear form a film on the skin of the fetus, which protects against external influences.

The fetus is able to swallow from around the 15th week of pregnancy and begins to drink amniotic fluid. The kidneys have started to work and excrete the absorbed amniotic fluid in the form of urine. The first breathing movements are also practiced and support the development of the lungs.

The unborn child moves a lot in the amniotic fluid and can now, for example, put its fingers in its mouth. Sleeps only briefly and irregularly. At the end of the 16th week of pregnancy, the fetus is around 18 centimeters tall.

What happens from the 17th to the 20th week of pregnancy (5th month)?

The senses develop. The fetus can distinguish between light and dark and the first eye movements are possible. Another milestone concerns the ears: the inner ear is now so well developed that the unborn child can perceive the first acoustic stimuli, initially noises from the mother's body, later from outside.

The movements of the unborn child become stronger, it twists and turns and “does somersaults”. Most mothers can feel the baby's small bumps for the first time during these weeks. The external genital organs can be recognized by a doctor during an ultrasound examination. The proportions of the fetus change, the head no longer appears as large as before compared to the body. The legs are now longer than the arms, and the facial features are also becoming more childlike. By the end of the fifth month, the fetus is just over eight inches.

What happens from the 21st to the 24th week of pregnancy (6th month)?

Half of the pregnancy is now over. The brain grows particularly quickly, and the nervous system and reflexes keep developing. This also includes the sucking reflex, which the fetus regularly exercises in the form of thumb sucking. In addition, the fetus now clearly reacts to noises from outside.

The intestines are also working, and the first stool accumulates. This is called meconium and is excreted in the first few days after birth. In stressful situations (e.g. infections, contact with harmful substances, stress at birth) it can happen that the first stool is passed on while still in the uterus. This can have dangerous consequences for the child (e.g. severe pneumonia due to meconium aspiration during the birth process).

The skin of the fetus is still pale and translucent in the 6th month of pregnancy. The previously missing fatty tissue is now increasingly formed, which means that the currently very thin fetus is steadily gaining weight. The so-called brown adipose tissue, which is particularly present in unborn and newborn children, also supports the heat balance. The first hairs as well as the beginnings of eyebrows and eyelashes are now there, and fingernails and toenails have formed.

At the end of the 24th week of pregnancy, the fetus is about 26 centimeters tall and about three quarters of a kilo.

What happens from the 25th to the 28th week of pregnancy (7th month)?

The organs of the fetus are largely developed and functioning, only the lungs are not yet fully developed, this lasts until shortly before the due date. The bronchial system and the lung cells are already so developed by the 25th week of pregnancy that in the event of a premature birth with appropriate intensive medical support, the first realistic chances of survival would exist. Around the 26th week of pregnancy, the lung cells also begin producing what is known as surfactant, another important step towards survival: Surfactant is a substance that surrounds the alveoli like a film and ensures that their surface tension is reduced. This is an important prerequisite for functioning breathing,this is the only way for the alveoli to develop sufficiently while breathing.

The fetus's eyes can always open briefly. He's now also having regular hiccups. These rhythmic contractions of the diaphragm support the development of the respiratory muscles. The whole body of the fetus "bounces" up and down, the pregnant woman can perceive these movements.

The child begins to sleep for several hours and to develop a sleep-wake rhythm. It can be woken up by movements or loud noises. At the end of the 27th week of pregnancy, the fetus is around 36 centimeters tall.

What happens from the 29th to the 32nd week of pregnancy (8th month)?

The fetus is now gaining weight rapidly and continuing to mature. Fat continues to accumulate under the skin, and the skin becomes smooth. The fingernails and the hair as well as the eyelashes and the eyebrows have grown significantly. At the end of the eighth month, the child weighs around two kilograms.

The further the pregnancy has progressed, the less space the unborn child has in the uterus. Extensive movements are no longer possible. In this phase the fetus turns into the birth position, later a complete turn is only possible with difficulty. Most births take place in what is known as the skull position, which means that the child lies head down in the mother's pelvis. This is the optimal location for a natural birth. More on the topic: The natural process of childbirth

Towards the end of the pregnancy or when the child slips deeper into the pelvis, the pregnant woman can repeatedly go into pre- or pelvic labor. These are a sign that the body is slowly preparing for birth. More on the subject of labor and delivery

What happens from the 33rd week of pregnancy to the birth?

In the last few weeks before birth, the child continues to mature. The brain in particular takes further important developmental steps and the lungs get ready for the first breath. From around the 35th week of pregnancy, surfactant is produced in the child's lungs in such large quantities that breathing would be possible without assistance. At an earlier point in time, surfactant production can be stimulated with medication if there is a threat of premature birth.

The senses are now also largely mature. However, clear vision is not yet possible even at birth; newborns only perceive their surroundings in a shadowy manner. At first you can mainly recognize light-dark contrasts, patterns and shapes. Spatial vision develops at around three months and by one year the child has achieved around 50 percent of the visual acuity of an adult.

The height with which the child will be born is reached some time before the due date, in the last few weeks the focus has been on weight gain. The lanugo hair disappears as the pregnancy continues. The amount of amniotic fluid also decreases continuously.

From the 37th week of pregnancy, the child is so developed that it is no longer considered a premature birth when it is born. Very few children are born exactly on the calculated due date. If the deadline is exceeded by 14 days, one speaks of a transfer. A pregnancy that is too long goes hand in hand with the risk of complications (e.g. difficult birth due to excessive birth weight of the child, underactive placenta), which is why the birth is usually initiated in these cases.

There are some signs that indicate that giving birth is not long in coming. More on the topic: The birth is announced.

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