What are the stages of fetus formation in the third month?

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 What are the stages of fetus formation in the third month?


What are the stages of fetus formation in the third month?


Fetal development stages by weeks


A typical pregnancy lasts about 40 weeks; It starts from the first day of the last menstrual cycle until birth and is divided into three phases or seasons in which the fetus grows and develops in a certain way, The first trimester or trimester begins from the first week of pregnancy and ends with the end of the thirteenth week, followed by the second trimester, which starts from the fourth week The tenth and continues until about the twenty-sixth week, then ends with the third trimester that extends until birth, i.e. the fortieth week, and the following is a description of these chapters in some detail:

first trimester


The following is a description of the stages of fetal development in the weeks of the first trimester of pregnancy:



  1. In the first week: in which the body prepares for pregnancy by increasing the thickness of the lining of the uterus (Uterus) so that it can harbor and nourish 
  2. the fertilized egg as soon as it is implanted in its lining. Depending on the first day of a woman's last menstrual period.
  3. The second week: Ovulation occurs at the beginning of this week, and the egg is fertilized approximately 12-24 hours later by the sperm, 
  4. and once fertilized, it begins to divide into multiple cells through a series of complex processes, 
  5. and that is during its transit down the fallopian tube, Then it enters the uterus and begins implantation in its lining.
  6. The third week: in which the fertilized egg implants in the lining of the uterus rich in nutrients, then it is called the blastocyst or blastocyst (English: Blastocyst), 
  7. as it is a very small ball consisting of hundreds of cells that multiply rapidly and develop into a fetus, 
  8. and to stop the ovaries from releasing more From the eggs, these cells later produce the pregnancy hormone (pregnancy hormone), which is scientifically known as human chorionic gonadotropin, or hCG.
  1. Fourth week: The fetus is now attached to the wall of the uterus, and the cells continue to divide that will form its organs in the near period, 
  2. and it may be seen by ultrasound, but it is smaller than a grain of rice, and here begins the formation of the amniotic sac, 
  3. or what is known as the pregnancy sac (English: Amniotic sac It is more like a fluid-filled pillow that surrounds and protects the fetus during its growth, 
  4. and the sac is connected to the yolk sac or umbilical sac (in English: Yolk sac) to provide the fetus with nutrients during the first weeks.

  • The fifth week: It may be possible to notice the fetal heartbeat during the ultrasound, but it cannot be heard at this stage. It consists of three distinct layers that develop over time to later form its organs and tissues, and these layers are:

  1. The ectoderm (Latin: ectoderm), will form the nervous system and many connective tissues, the two ears, the inner ear, and the eyes.
  2. The endoderm or the inner layer will grow into internal organs such as the bladder, lungs, and intestines.
  3. The mesoderm will form the circulatory system, heart, and later reproductive organs, kidneys, muscles, and bones.
  4. the Sixth week: At the end of the sixth week, the size of the fetus will have tripled, two hemispheres of the brain will be formed, 
  5. and brain waves can now be recorded. As for the heart, it beats regularly at a rate of about 150 beats per minute, 
  6. which is equivalent to twice the average heart rate of adults However, the pulse is still weak, so it cannot be heard with a stethoscope.
  7. Seventh week: The brain of the fetus at this stage is growing more complex, and the doctor may be able to clearly see it inside the transparent skull. 
  8. For the fetus, dark spots indicate the location of the eyes and nostrils, and a small part of the mouth and ears also begins to form.

  • The eighth week: Several developments occur, as follows: 

  1. The fetus's facial features are slowly but clearly defined, including its upper jaw and nose, small bumps are formed where the ears will form, eyes become more prominent, and the folds of the eyelids that partially cover them appear, and for its size, it is about the size of a bean, and the size of its head is larger than its body so that Bend toward the chest.
  2. The limbs appear more clearly, and the fetus’s hands develop bumps where the fingers will be. The fetus’s legs and feet develop after about five days of the growth of its arms and hands, and the shape of its feet begins to appear, but the fingers are not formed in them.
  3. The part responsible for the sense of smell is forming in the brain, in addition to the fact that nerve cells in the brain begin to branch out to form early neural pathways.
  4. The embryonic tail nearly disappears to form the coccyx bone.
  •  “The ninth week:” in which the heart is almost divided into four chambers and all the basic organs of the fetus are in their correct place to some extent, and by the end of this week it will become the size of a grape, as it will reach about 2.3 centimeters in length and weigh about 2 grams, and as the tail of the fetus approaches to disappear He will look more human, and the following developments will occur in him: 

  1. The placenta has developed enough to be responsible for its growth after that, it will be almost ready to deliver the nutrients the fetus needs and remove waste from its body, and it is noteworthy that until this stage the ovaries were responsible for producing the hormone progesterone necessary for its growth.
  2. The genitals begin to form, but it is not possible to know the sex of the fetus by ultrasound at this stage.
  3. His nose and sense of smell are developing, the little ears are more defined and will move into place soon, and his gums will develop buds that will develop into milky teeth later in pregnancy.
  4. His ankles and wrists are more developed, and his fingers and toes are more clearly defined.
  5. His arms can be bent at the elbows and long enough for his hands to rest on his chest but not meet, plus his legs are getting longer and in proportion to the rest of his body, and his knees and ankles are also visible.
  6. the Tenth week: In the past weeks, the fetus was in its embryonic stage in which the cells necessary to form its main organs, limbs, brain, and nervous system are formed, and this week it will move to a stage in which it grows clearly and continuously until it is ready to exit the uterus, and in this week the yolk sac, which It provided the fetus with nutrients before the growth of the placenta, and it is indicated that its weight here is about 4 grams, and its length is about 3.1 from head to rump so that it is about the size of green olive, and you will notice the following developments on the fetus: 
  7. His heart is fully developed and beating at a rate of 180 beats per minute.
  8. Other vital organs, including the brain, intestines, kidneys, and liver, which are responsible for making red blood cells, begin to function instead of the yolk sac, and it is worth noting that they will continue to grow throughout pregnancy.
  1. The fetus moves its arms and legs in a circular motion at the shoulder and hip joints, and its hands may meet above the area of ​​its heart, as the limbs at this stage have developed very well, although it is still a small fetus, it is very active.
  2. His head becomes more rounded and straight, the development of the ears on the outside is almost complete, and his eyelids are joined and will remain that way until the 27th week of pregnancy.
  3. Eleventh week: The fetus becomes more active, although the pregnant woman may not feel any of its movement, and this week the iris grows, its eyes, and fingernails, and its length from the front of its head to its buttock is approximately 5 centimeters, and most of its length is caused by The length of its head, which constitutes about half of its entire body, and here it is about the size of a peach.
  4. Twelfth week: The muscles of the fetus grow in this week, which enables it to start opening and closing its fingers and toes, bending its toes, kicking its arms and leg, in addition to the development of its reactions, as the doctor may notice it when the mother places her hand on her stomach, and the fetus vibrates in response to that. , but until this stage, the pregnant woman may not feel his movement yet.
  5. the Thirteenth week: During this week, the fetus becomes able to put his thumb in his mouth, and day after day his face looks more human-like, as his eyes move from the sides of his head to the front of his face, and they may appear blue, brown or green, and his ears move to their place, and he grows His torso is faster, and his arms are getting longer to fit more in proportion to his body.


second trimester

By the beginning of the second trimester, the size of the fetus is still small, and it is worth noting that by skipping the first three months, the risk of miscarriage decreases, 

and the early pregnancy symptoms that the pregnant woman experiences such as fatigue and morning sickness begin to disappear, 

and she may feel more energetic and can exercise Exercise after referring to her doctor to take medical advice about 

the appropriate sport for the pregnant woman in general and for her health condition in particular, and the following is a description of this stage of pregnancy in detail:




  • The fourteenth week: At this stage, the length of the fetus from the top of its head to its rump has reached about 10 cm, its weight is about 127 grams, and its size is the size of a small peach. By the time of birth, in addition to this, 
  • his fingerprints, including his thumb, develop this week, and he begins to swallow a small amount of amniotic fluid, and it passes through the stomach to begin the work of the kidneys, and this fluid is excreted again into the amniotic fluid in the form of urine.
  • The fifteenth week: Although the fetus's eyes are still closed at this stage, they become sensitive to light, as they may sense bright light outside the abdomen, and the fetus also begins to hear some sounds made by the digestive system and the outside world, and the mother's voice and heartbeat. 
  • Sixteenth week: The continuation of the development of the fetus's nervous system enables it at this stage to bend its limbs, and the meeting of its hands may also be possible.
  • Seventeenth week: The weight of the fetus in this week is approximately 150 grams, and he can now open and close his mouth, in addition to having a strong fist, as for his eyes, they begin to move even though they are still closed, and the growth of eyebrows and eyelashes also begins. 
  • The eighteenth week: The weight of the fetus is now 200 grams, its length from head to buttock is approximately 14 centimeters, and its eyes are directed forward while the ears take their place on either side of his head, and his digestive system begins to work.
  • The nineteenth week: If the fetus is a female, the formation of the uterus and vaginal canal will begin. In general, the fetus in this week develops a protective fatty layer similar to a cheese called Vernix caseosa, 
  • which helps protect its thin skin from erosion and cracking as a result of exposure to liquid. Amniotic.
  • Week 20: This week in the middle of the pregnancy period. The length of the fetus from its head to the buttock is about 16 centimeters and weighs more than 320 grams,
  •  and its movement accelerates at this stage, and it sleeps and wakes up regularly, and it may be awakened by its mother’s movements or external noises.
  • The twenty-first week: The sucking reflex has now developed, which enables the fetus to suck its thumb, and by the end of this week, 
  • the fetus's body will be completely covered with fluff, as the fluff also helps it to install a greasy coating on its skin.[9]
  • Twenty-second week: The length of the fetus from head to rump is now 19 centimeters and weighs approximately 460 grams, and his hair and eyebrows begin to appear, 
  • and brown fat is formed responsible for the production of heat for the fetus, 
  • and if the fetus is male, then his testes begin to descend into their natural position.
  • Twenty-third week: This week, the edges may form in the palms of the fetus’s hands and the soles of its feet, which will later develop into fingerprints and footprints, and the mother may notice vibrating movements when her fetus suffers from hiccups, in addition to The fetus begins to move its eyes rapidly.
  • The twenty-fourth week: In this week of pregnancy, the length of the fetus from head to buttock will be approximately 21 centimeters, 
  • and its weight will be more than 630 grams. The result of visible blood in the capillaries.
  • Twenty-fifth week: At this stage, the fetus spends most of its sleep time in what is known as rapid eye movement (REM) sleep with its eyelids closed, 
  • and it may be able to respond to familiar sounds such as its mother's voice.
  • Week 26: The fetus may be 23 centimeters long from head to rump and weigh 820 grams, and its lungs will now begin to produce what are known as surfactants or surfactants, 
  • the substance that allows the air sacs in the lungs to inflate and prevent them from attaching to each other when they contract.

third trimester



In this last stage of pregnancy, the weight of the fetus will increase rapidly, and every week of its growth will help the fetus prepare for birth, and the following is a description of this stage in detail:

  • The twenty-seventh week: The pregnant woman will now feel the movements of her fetus resulting from the hiccups, 
  • and it is worth noting that the hiccups usually appear as a result of involuntary movements of the diaphragm (in English: Diaphragm), 
  • and because the trachea of ​​the fetus is filled with water, the hiccups are not accompanied by sound. 
  • The twenty-eighth week: In this week, the length of the fetus from its head to the buttock may reach 25.4 centimeters, its weight is approximately 1.13 kilograms, and its eyes become partially open.
  • Week 29: The fetus can now stretch and kick and simulate a grasping motion.
  • The thirtieth week: This week, the fetus will be more than 27 centimeters long from head to buttocks and weigh approximately 1.3 kilograms, 
  • and red blood cells will begin to form in its bone marrow, and its lungs will be able to breathe, but they may need medical help outside the womb, 
  • so it will remain Almost all fetuses born during this period are alive if they receive intensive care services and in addition to this, 
  • the hair of the fetus will increase in thickness, and it will be able to cry and open its eyes completely. 
  • Thirty-first week: At the end of this week, the fetus will have completed most of the main stages of its development, and will begin to gain weight rapidly.
  • Thirty-second week: The length of the fetus from its head to its buttock will be 28 centimeters, its weight is approximately 1.7 kilograms, and the fluff that covered its body will begin to fall off, and its toenails will appear. 
  • Thirty-third week: During this week, his bones harden, but the skull bone remains soft and flexible, and the size of his pupil may change in response to light.
  • Thirty-fourth week: The fetus is now about 30 centimeters long, weighs about 2 kilograms, its nails are as far as the tips of its fingers, and its skin is smooth and pink.
  • Thirty-fifth week: His limbs are full, and his skin is smooth and free of wrinkles. 
  • The thirty-sixth week: The length of the fetus from its head to its buttock is about 31.7 centimeters, and its weight is approximately 2.5 kilograms.
  • 37th week: The fetus is now ready to be born, and its length from head to heel is about 48.6 centimeters, 
  • and its weight is more than 2.9 kilograms. His growth for several years after his birth, and the length of his toenails are complete, 
  • In addition to the continued movement of his facial muscles, so he can frown, and his sense of hearing has now become more sensitive, 
  • as the mother notices his movements in response to certain sounds, 
  • and it is indicated that the doctor should be consulted in case the pregnant woman notices a change in the pattern His movement is more than usual. 
  • The 38th week: The weight of the fetus may be more than 2.9 kilograms, and a large part of this weight is a layer of fat that contributes to keeping it warm when it comes out of the womb and activates its reactions such as grasping hands and sucking, 
  • which helps it to breastfeed later. As for its organs, 
  • all of them work; As the brain has now begun to control all body functions, including breathing and regulating the heartbeat, but in return its growth rate has slowed.
  • Thirty-ninth week: The length of the fetus from head to heel is 50.7 centimeters, and it weighs more than 3.3 kilograms, and in this week, the thickness of its skin increases and becomes pale, and it is indicated that the lungs will produce more surfactants, and thus the child is ready to breathe outside the womb. 
  • The fortieth week: This week is the expected date of birth, 
  • and the fetus is in full size and is estimated at an average of 50.8 centimeters in length, 
  • and approximately 3.2 kilograms, but it is noteworthy that these remain estimates and there is a difference in the sizes of newborns, as well as the date of birth, 
  • which may be delayed in some cases For the scheduled appointment, therefore, it is recommended to see a doctor to determine the appropriate procedure.


birth stage


By the end of the third trimester of pregnancy, the pregnant woman’s body will begin to show signs of imminent delivery, and the process that leads to the birth of the fetus is known as labor or labor, and here are some of the symptoms that precede its occurrence and indicate its approach, noting that each labor and birth include certain stages, Each birth differs from the one before it and the one that follows it:


  • Vaginal mucous discharge containing blood.
  • Feeling of increased pressure in the uterus and pelvic area.
  • Changes in the energy level of a pregnant woman.