Pregnancy is a sweet yet difficult time. However, knowing the developmental stages of the fetus in the mother’s womb and what happens during this period makes us spend this period with more awareness and we can better create the necessary conditions for this period. 

Pregnancy,  In this article, we intend to describe the developmental stages of the fetus from fertilization to birth using valid and approved information by experts and examine the developmental process of the fetus in the mother’s womb on a weekly, monthly and quarterly basis. 

In this review, we provide information including what condition the baby is in at each stage and what changes we should expect in the mother’s body.

Beginning of pregnancy, from fertilization to diagnosis

Start of pregnancy

The onset of pregnancy is the first day of the most recent menstrual period . This is called the gestational age or menstrual age, which is about 2 weeks ahead of the fertilization time. The date of the first day of the most recent menstrual period is an important date that will be important in determining the approximate time of delivery.

Each month, the body goes through a reproductive cycle that ends with either menstruation or pregnancy. This cycle occurs continuously during the reproductive years (from puberty in adolescence to menopause around the age of 50).

How to fertilize

There are several stages in the cycle that leads to pregnancy. First, a group of eggs are prepared to leave the ovary and ovulate. These eggs grow in small, fluid-filled cysts called follicles. One of these eggs matures and continues the cycle. The follicle of this egg suppresses all the other follicles in the group and stops the growth of other follicles. The mature follicle opens and releases the egg from the ovary. This process is called ” ovulation “. Generally, ovulation occurs about 2 weeks before the start of the next menstrual period (mid-cycle).

After ovulation, the open follicle becomes a structure called the corpus luteum. The corpus luteum secretes the hormones progesterone and estrogen . Progesterone helps prepare the endometrium (the lining of the uterus). This cover is where the fertilized egg settles for growth. If you do not become pregnant during the cycle, the lining of the uterus will collapse and be destroyed during menstruation.

On average, fertilization occurs about 2 weeks after the last menstrual period. When sperm penetrates the egg, changes occur in the egg’s protein coat to prevent other sperm from entering.

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After fertilization

Within 24 hours after fertilization and fertilization, the egg cell begins to divide rapidly into large numbers. These cells remain in the fallopian tube for about 3 days after fertilization. The fertilized, divided egg, now called a blastocyte, continues to divide as it passes slowly through the fallopian tube and reaches the uterus. When the blastocyst reaches the uterus, it attaches to the endometrium. This is called implantation.

The blastocyst comes out of its protective covering before implantation. When a blastocyst comes in contact with the endometrium, they both exchange hormones to help the blastocyst attach. Some women notice spotting (partial bleeding) within 1 or 2 days of implantation . Spotting is normal and there is no reason to worry. At this point, the endometrium thickens and the cervix or cervix (the opening between the uterus and the birth canal) closes with cervical plaque mucus .

Within 3 weeks, the blastocyst cells form a small ball called an embryo. During this time, the baby’s first nerve cells are formed.

Time to diagnose pregnancy and see a doctor

From the moment of fertilization, hormone H. سی. GC (hCG) or Human Chorionic Gonadotrophin is present in the blood. Cells make this hormone that forms the placenta, or baby’s food source, in the womb. اچ. سی. G is a hormone that is detected in a pregnancy test. Although this hormone is present from the beginning, its increase in the body takes time. It usually takes 3 to 4 weeks after the first day of the most recent menstrual period for the H hormone. سی. Increase as much as can be detected in pregnancy tests.

You should see a doctor when your pregnancy test is positive. If etched. سی. If there is enough J in the bloodstream, the pregnancy test will be very accurate. Usually a few weeks after fertilization, the etching level. سی. Blood is enough to test for pregnancy.

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Child development timeline

The baby changes a lot during pregnancy. Pregnancy is divided into three stages called trimesters, each lasting about 3 months. The doctor usually talks about the developmental stages of the fetus on a weekly basis; So if you are 3 months pregnant, about 12 weeks have passed since your pregnancy. During each trimester, you will notice certain changes in your baby and yourself.

Normally, pregnancy is considered a nine-month process; But this is not always the case. A full-term pregnancy is 40 weeks or 280 days. Depending on what months you are pregnant (some months are shorter and some are longer) and in which weeks you give birth, your gestation period may be 9 or 10 months. This is perfectly normal and not a problem.

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Stages of human embryo development week by week, monthly and quarterly

First three months

After fertilization and implantation, the baby is initially just an embryo: two layers of cells that make up all the organs and parts of the body. The baby, which grows rapidly, will soon be the size of a red bean that is constantly moving. His heart beats fast and his intestines form. The earlobes, eyelids, mouth and nose of your growing child are also slowly forming.

First month (weeks 1 to 5)

As the fertilized egg grows, an impermeable sac forms around it, which gradually fills with fluid. This sac is called the amniotic sac and is effective in trapping and protecting the growing embryo. During this time, the placenta also forms. The placenta is a round, flat organ that carries nutrients from mother to baby and carries waste products from the baby’s body. The placenta is the baby’s food source during pregnancy.

In the first few weeks, the baby has a rudimentary face in which the eyes are large, dark circles. The mouth, jaw, and throat are also forming. Blood cells form and blood flow begins. By the end of the fourth week, the fetal heart tube is beating 65 times per minute.

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At the end of the first month, the baby is about 6 mm long, which is smaller than a grain of rice.

• second week

The second week of pregnancy is an important week. You ovulate this week and if the egg encounters sperm, you will become pregnant.

• Third week

The baby is a small ball, called a blastocyst, made up of several hundred cells that multiply rapidly.

• forth week

Your baby is an embryo deep in the womb that is made up of two layers and the initial placenta is forming.

• Fifth week

Your little embryo is growing crazy and you may experience discomfort from pregnancy such as breast pain and fatigue.

Second month (weeks 6 to 9)

Child facial features are still taking shape. Each ear begins as a small crease in the scalp. Small buds also form that eventually grow into limbs. The toes and eyes are also forming.

The neural tube (brain, spinal cord, and other central nervous system tissues ) is now well formed. The formation of the gastrointestinal tract and sensory organs also begins. The conversion of cartilage to bone also begins. At this point, the baby’s head is larger than the rest of the body. The baby’s heartbeat is usually recognizable around the sixth week. After the eighth week, the baby is called an embryo instead of an embryo.

At the end of the second month, the baby is about 2.5 cm long and weighs about 37 grams.

• Week Six

The baby’s nose, mouth, and corners begin to form. You may experience morning sickness and spotting.

• Seventh week

The baby’s arms and legs, which are still embryos with small tails, are forming and the size of the uterus has doubled.

• Eighth week

The child is constantly moving; But you can not feel it. In the meantime, you may be deciding on pregnancy tests.

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• Ninth week

The fetus, which is now about 2.54 cm long, looks more like a human. You have probably noticed an increase in the size of your waist.

Third month (weeks 10 to 13)

The arms, hands, toes and feet are fully formed. At this point, the child begins to explore and do a little curiosity by doing things like opening and closing the fists and mouth. The formation of toenails begins and the outer corners are formed. Tooth buds form under the gums. The baby’s reproductive organs also grow; But the sex of the fetus is difficult to determine on ultrasound.

By the end of the third month, the baby is fully formed. All organs and organs (arms and legs) are created and continue to grow to function. The baby’s circulatory and urinary systems also work, and the liver produces bile. Because the most critical stages of fetal development have taken place, the risk of miscarriage is significantly reduced after 3 months .

At the end of the third month, the fetus is 10 cm long and weighs 28 grams.

• Tenth week

The most important part of the fetal development period is over. The organs and structures are in place and ready to grow.

• Eleventh week

Soon the fetal arms open and close in fists, and tooth buds appear under the gums.

• Twelfth week

Your little toes can bend. His brain grows frantically and his kidneys begin to urinate.

• Week 13

This is the last week of the first quarter. Your baby now has delicate fingerprints.

Second trimester of pregnancy

Usually the second trimester or mid-pregnancy is the best part. By this time, morning sickness has probably gone away and the discomfort of early pregnancy is gone. During this period, the development and formation of fetal facial features begin. During this time, her unique little fingerprints are formed, and her heart pumps 25 quarts (about 25 liters) of blood daily.

As the weeks go by, the fetal skeleton forms. Also, the soft cartilage gradually hardens and turns into bone, and the fetus acquires the ability to hear. You will probably feel him kicking and shaking soon; Of course, if you have not felt it yet.

During this trimester, many people become aware of their baby’s gender. The sex of the baby is usually determined by an anatomical scan around the 20th week. Anatomical scan is an ultrasound that examines the physical development of the fetus.

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Fourth month (weeks 14 to 17)

The fetal heartbeat may be audible with a device called a Doppler. The toes are perfectly marked. Eyelids, eyebrows, eyelashes, nails and hair are formed. Teeth and bones also become denser. The fetus can even suck on its thumb, yawn, stretch, and change the shape of its face.

The nervous system begins to work. The limbs and genitals are now fully formed and the doctor can see on the ultrasound if your baby is a girl or a boy.

By the end of the fourth month, the fetus will be about 15.2 cm long and weigh 113 grams.

• Fourteenth week

The small, delicate face of the fetus takes on different states, and you may feel more energetic and less nauseous.

• Fifteenth week

The fetus can sense light and taste buds are forming. Do you have nasal congestion and runny nose? This is one of the strange side effects of pregnancy.

• Week 16

Be prepared for a leap in your child’s development. In the next few weeks, the weight of the fetus doubles and several centimeters increase in length.

• Seventeenth week

The skeleton of the fetus changes from soft cartilage to bone, and the umbilical cord becomes stronger and thicker.

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Fifth month (weeks 18 to 21)

At this point, you may feel the fetus move around. The fetal muscles are forming and he is using them. The first fetal movements are called quickening, which creates a feeling of fullness. Hair grows on the fetal head. The shoulders, back and temples of the fetus are covered with thin, soft hair called fetal hair . These hairs protect the fetus and usually fall out at the end of the first week of life.

The skin of the fetus is covered with a white coating called Vernix caseosa. This “cheese-like” substance is thought to protect fetal skin from prolonged exposure to amniotic fluid. This cover sheds just before the baby is born.

At the end of the fifth month, the fetus is 25 cm long and weighs about 250 to 500 grams.

• 18th week

The fetal reproductive system is so large that it can be seen on ultrasound. Are you hungry? An increase in appetite is normal at this time.

• Week 19

The fetus can probably hear you! If your sides hurt, it may be due to round ligament pain.

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• Week 20

Congratulations. You are now half pregnant. The fetus swallows more nutrients and produces meconium .

• Twenty-first week

Do you feel the fetus moving? Those initial shocks have now turned into full-fledged kicks and he now has eyebrows!

Sixth month (week 22 to 25)

If you could look inside the uterus, you would see that the skin of the fetus is red and wrinkled, and the veins can be seen from behind the translucent skin of the fetus. The fingerprints of the fetus’ toes can also be seen. At this stage, the eyelids separate and the eyes open.

The fetus responds to sounds by shaking or shaking. When the fetus is hiccuping, you may notice rapid movements. If a baby is born prematurely, it may survive after 239 weeks with intensive care.

At the end of the sixth month, the fetus is about 30 cm long and weighs 900 g.

• Twenty-second week

The fetus looks like a miniature baby and your abdomen is enlarged.

• Twenty-third week

When you move, the fetus can feel it. You may soon notice swelling in your ankles and feet.

• Twenty-fourth week

Your baby is like a bunch of corn, tall and thin, and your growing uterus is the size of a soccer ball.

• Twenty-fifth week

Your small body fat will increase and you will lose more hair. Your hair may also be very shiny.

Third quarter

By the beginning of the third trimester, the fetus weighs about 1 kg. He can blink and now his eyes have eyelashes. As fat accumulates under the fetus’s wrinkled skin, its skin gradually becomes smoother. Hand nails and real hair (or at least some fluffy hair) also form, and billions of neurons form in his brain.

During the third trimester, the fetus gains weight rapidly and body fat increases, which is beneficial after birth. In the full term, each baby averages more than 48 cm in length and weighs approximately 3.2 kg.

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Do not forget that pregnancy can last up to 10 months. A typical full-term pregnancy is 40 weeks, which may enter the tenth month. The delivery date may also be 1 or 2 weeks (41 or 42 weeks) after the approximate time of delivery. Your doctor will monitor you closely as you approach the time of delivery. If the due date expires and the spontaneous labor is not performed, the doctor may use induced labor; That is, to prescribe drugs to induce labor. Be sure to talk to your doctor about your baby’s birth plan during this trimester.

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Seventh month (weeks 26 to 29)

The fetus continues to grow and increase its fat stores. At this point, his hearing is fully developed. The fetus regularly changes position and responds to stimuli such as sound, pain, and light. Amniotic fluid begins to decrease. If the baby is born prematurely, it will probably survive after the seventh month.

At the end of the seventh month, the fetus is about 35.5 cm long and weighs between 1 and 2 kg.

• Twenty-sixth week

The fetus injects a small amount of amniotic fluid into the lungs, which is a good exercise for breathing.

• Twenty-seventh week

Do you feel tickled? It may be due to hiccups in the fetus. The fetus opens and closes its eyes and even sucks its fingers.

• Twenty-eighth week

The fetus’ eyes may now be able to see the light that passes through the uterus.

• Twenty-seventh week

The fetus’s muscles and lungs continue to grow and develop, and its head becomes larger to make room for its growing brain.

Eighth month (weeks 30 to 33)

The fetus continues to grow and increase its fat stores. You may feel that the child kicks more. The fetal brain is growing rapidly at this time and it can see and hear. Most of the body’s internal systems are well developed; But the lungs may still be immature.

At the end of the eighth month, the fetus is 45.7 cm long and weighs about 2.3 kg.

• Week 30

The fetus now weighs approximately 1.36 kg. In the meantime, you may experience mood swings, clutter, and fatigue.

• The third week

The baby’s strong kicks will keep you awake at night, and you may also feel Berxton Hicks contractions .

• Seventy weeks

The fetus is gaining weight! Enlargement of the uterus may also cause heartburn and shortness of breath.

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• Thirty-third week

Due to the fact that the fetus weighs more than 2 kg, you are probably walking crooked and heavy and have trouble sleeping in bed.

Ninth month (weeks 34 to 37)

During this stage, the fetus continues to grow and mature. At this point, the lungs are close to full growth and maturity. Fetal involuntary reactions are also coordinated; Thus, he can blink, close his eyes, turn his head, hold things tightly, and react to sound, light, and touch.

At the end of the ninth month, the fetus is about 43 to 48 cm long and weighs 2.5 to 3 kg.

• 34th week

The fetal central nervous system and lungs are evolving, and confusion and fatigue may slow you down.

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• 35th week

The fetus in the womb is very comfortable and calm and does not turn its back; But you can still feel his repetitive movements (which, of course, are not very previous).

• Week 36

The fetus gains about 28 grams per day. As you approach the due date, you may feel her go down into the pelvis.

• Week 37

The fetal brain and lungs continue to grow. You may have vaginal discharge and occasional contractions.

Tenth month (weeks 38 to 41)

In the final month, you may give birth at any time. You may find that your baby’s movements are reduced due to lack of space. At this point, the condition of the fetus may change to prepare for birth. Ideally, the fetal head is located at the bottom of the uterus. You may feel uncomfortable; Because the fetus falls down into the pelvis and prepares for birth.

By the end of the tenth month, the fetus is 45.7 to 50 cm long and weighs about 3.2 kg.

• The thirty-eighth week

The fetus has a lot of power in grasping things, which you can try soon when you first hold his hand! In the meantime, watch out for the signs of preeclampsia .

• Week 30

During this week, your fetus is in full term and you are approaching delivery. In the event of rupture of the water bag baby , contact your doctor.

• Fortieth week

The fetus is now as small as a pumpkin! If you are still pregnant and have not given birth, do not worry. It is common to continue the pregnancy until after the due date or time of delivery.

• Forty-first week

The fetus can no longer remain inside the uterus. At this time, you should give birth or use induced labor.

Stages of twin fetus development

In the following, we describe the developmental stages of heterogeneous twin embryos from the moment of implantation to the time of birth.

Third week

In heterogeneous twins, each baby is born from a separate fertilized egg. By the third week, each egg cell has become a ball containing several hundred cells, called blastocytes, that nest inside the lining of the uterus.

forth week

The twins are now embryos. The embryo is made up of two layers of cells that make up all the organs and parts of the body. By next week, each embryo will have its own amniotic sac and placenta.

Eighth week

After eight weeks, the twins have arms and legs that bend and their hearts beat for two weeks. Nerve cells in the brain branch to communicate with each other.

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Twelfth week

The twins are kicking and pulling. Their hands are on their hearts and their little nails are starting to grow. The eyelids also cover the eyes and tooth buds are forming under the gums.

Week 16

Children now have their own unique fingerprints. They can change the shape of their face and look with half-open eyes and expel the amniotic fluid they have swallowed. With ultrasound, you can see their genitals.

Week 20

Talk to your twins. Maybe they can hear you. At this time, hair grows on their scalp and a greasy, white coating forms on their skin, which protects them from prolonged exposure to amniotic fluid.

Twenty-fourth week

Children’s eyebrows are growing. The buds of deciduous and permanent teeth are in place, and the taste buds are probably working now. Whatever their skin color after birth, they have red and wrinkled skin at this time.

Twenty-eighth week

Twins can open their eyelids and have eyelashes on their eyelids. Layers of fat are formed under the skin, which makes their skin smooth. They can suck their fingers and you may feel them hiccuping.

Seventy weeks

The toenails are now formed. Their arms, legs and torso are filling up. Some children even have a head full of hair at this time. Most twins are born in the next few weeks.

Week 36

The average gestational age of twins at birth is 36 weeks. Their lungs have grown well by the 34th week. They spend the last few weeks storing fat and gaining weight. The average weight of twin babies is 2.5 kg.

Some terminology of late pregnancy

As you approach the end of your pregnancy, there are categories and terms about the time of delivery that you should be familiar with. These terms are used to describe the last few weeks of pregnancy, as well as the awareness of certain complications that may occur in the baby.

Respiratory, hearing, or learning difficulties are more likely to occur in infants born in the early term or earlier than in infants born a few weeks later and within the full term. . It’s best to know how to spell these terms. You may first see the week (38) and then see two digits separated by a slash (7.6). This means that you are now in the few days of your pregnancy; So 7.6 38 means that you are on the sixth day of the thirty-eighth week of pregnancy.

The last few weeks of pregnancy are divided into the following groups:

• Early term: 37 0.7 to 6/7 38;
• Full term: 39 0/7 to 6/7 40;
• Late term: 41 0/7 to 6/7 41;
• Post term: 42 0.7 and after.

Ask your doctor any questions you may have about your gestational age and approximate delivery time.

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Concluding remarks

In this article, we describe the stages of embryonic formation from the time of ovulation and fertilization to the formation of blastocytes and embryos and the growth and development of the embryo until birth. Because fetal growth is usually expressed on a weekly basis, the months are not precisely defined as 30 days, but are more limited to weeks.