Fertilization: Embryo Development, Fetus Development Steps

The journey of life begins with a single cell and later that cell divides itself into many cells together. During human embryonic development, a single cell begins our life journey, which later separates into a mass of many cells. In science, embryogenesis is the official name for the process of forming an embryo. In other words, this is what happens when fertilization takes place.

Key Terms: Fertlisation, Embryo Development, Fetus Development, Blastocyst, Placenta

What is Fertilisation?

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Growing new life is referred to as fertilization.The process of fertilization occurs in the female reproductive system by means of the fallopian tubes. 

• Several processes are involved in the formation of embryos before they reach the uterus, which is critical to their growth and development.
• A process by which the male sperm and female ovum are combined to form a child. 
• An embryo is made up of a zygote after fertilisation.

Journey of an Egg for Fertilisation

Read about: Internal Formation of Zygote

First step of the Fertilisation process

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When an egg cell has been fertilised in the fallopian tube, the process begins. Now that this fertilised egg cell has been divided into two cells, it then divides into four, and so on.

• Typically, this results in the formation of a ball-like structure inside of which many cells gather.  
• An individual with a number of sixteen has a ball-shaped structure known as a morula. Another ball-shaped structure called the blastula follows from this. 

Blastula

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There's nothing more than a swollen mass of cells that takes the shape of a blastula when they arrange themselves in a certain way. They align themselves into the end, leaving an empty space inside. Eventually, when it is filled with fluid, the structure will resemble the one below.

Function of a blastocyst

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The next phase in the development of an embryo is when the embryo will have cells that have already been differentiated and will even differentiate further. A cell differentiates from its surroundings when it gets differentiated from another nearby cell. In other words, we will be able to differentiate these cells into a whole new variety of cells once they have been divided multiple times.

• The Blastocyst stage consists of these differentiated cells combined in a mass. With the growth of this embryonic cell, it develops its body further.
•  An embryo will require proper nutrition for proper development and growth. An embryo can obtain this nutrition by ingesting milk from the mother. 
• Those nutrients can be provided by connecting the blastocyst to the correct location. 
• An important part of the implantation process is when that connection is made. 
• A blastocyst attaches to the uterus where it implants itself at a certain fixed position inside the uterus at this stage. During this phase, the baby grows inside the uterus.

Read More: Lactation

What is Placenta?

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A placenta grows inside the mother's uterus during pregnancy. Your growing baby relies on this structure to supply oxygen and nutrients while also eliminating waste. During pregnancy, your placenta attaches itself to the wall of your uterus, from which your baby's umbilical cord emerges.

An embryo attaches itself to the placenta for several reasons:

1. The process of obtaining nutrition
2. The act of shedding waste
3. An exchange of oxygen and carbon dioxide takes place

During pregnancy, the barrier between the mother and the baby called the placenta provides support for all of these things. As the baby's connection to the mother is the placenta, we can refer to the placenta as a relationship. As we reach the point of delivering a baby, the embryo begins to grow.

Fetal Stage

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The fetal developmental stage means that the baby's internal organs become identifiable at the point where they start developing. That's why the embryo is now referred to as a fetus. Once the fetus takes the proper amount of time to develop, it will continue to develop inside the uterus. In due course, the growth process will be complete, and the child will be all set to enter the world. In most cases, embryogenesis is carried out through this process.

Also Read:

Development of Fetus

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First month

Fertilized eggs are enclosed in a water-resistant sac as they grow, gradually absorbing liquid. The amniotic sac is to be referred to as that. The cushioning function of this sac is quite important. Additionally, the placenta is also developing during pregnancy. 

• It is a flat round organ that is attached to the placenta and helps transfer nutrients from the mother's body to the embryo, while also transferring the waste from the embryo back to the mother. 
• There will be large dark circles around the eyes during this primitive phase. As the mouth, lower jaw, and throat develop, there will be large dark circles around the eyes. These dark circles indicate that blood cells are forming and that circulation is beginning.
• In the fourth week of pregnancy, the little heart will beat 65 - 75 beats per minute. It will be almost as long as a grain of rice by the end of the month when compared to the embryo.

Second month

Embryos continue to develop their facial features here. Starting at the side of the head, an ear is shaped by a fold of skin. Tiny buds will form that will eventually become arms and legs. Meanwhile, fingernails and toes are also forming.

• At this stage, the central nervous system is well developed, including the neural tube that forms the brain, spinal cord, and other neural tissues. 
• Meanwhile, the digestive system and sensory organs are also developing.
• Lastly, the cartilage is replaced by bones. An embryo's head is larger than its body here when compared with the rest. An embryo weighs about one thirty of an ounce at the end of the second month and measures one inch across. 
• The heartbeat of the embryo can be detected after six weeks. A fetus is a completed embryo that has been in existence for eight weeks. 

Third month

As the baby reaches this stage, the development of his arms, hands, fingers, feet, and toes will be complete. In this developmental stage, the baby can open and close his or her mouth and fist. 

• In this phase, we will observe the outward development of external ears and the formation of external fingernails and toenails. It is at this stage that the baby's reproductive organs begin to form, however it will be difficult to determine the baby's gender through an ultrasound even at this stage.
• When the baby is fully developed in the third month, the gender can be determined through an ultrasound. During development, all organs and extremities will be present and will continue to mature until they are fully functional.
• Additionally, we can see that the kidney and the liver start functioning here along with the circulatory and urinary systems. It is expected that the baby will be about four inches long and weigh about one ounce at the end of the third month. 
• This stage that the baby has reached the crucial stage of its development, and the chances of a miscarriage have significantly decreased. 

Fourth month

With the help of a device known as the Doppler, we will be able to hear the heartbeat of the baby this month. During this time we will see how well the fingers and toes are defined. Aside from hair, nails, and eyelashes, eyelids, eyebrows, and eyelashes will also develop.

• The child possesses the ability to suck his or her thumb, yawn, stretch, and make faces at this stage as the density of his or her teeth and bones grows. 
• As the nervous system starts to function, the brain will also begin to function. Sexual organs and genitalia are completely formed. 
• Ultrasound tests can be used to determine the gender of the baby. The baby will be about six inches long and four ounces heavy by the end of this month.

Fifth month

The baby will be exercising his/her muscles and developing muscles at this stage. During this stage, you will feel your baby's movement. Quickening is the term used by medical professionals to describe the first movement you might feel. 

• The baby's hair begins growing on its head at this stage of development. Lanugo, the short hair used to cover the baby's back, shoulders, and temples, will cover the baby's back, shoulders, and temples.
• A baby's first hair is usually shed by the end of the first week after birth - it protects the baby. White skin on babies is known as vernix caseosa (meaning vernix sheet). By keeping the baby shielded from the amniotic fluid, this substance protects the baby from long-term exposure. The skin covering this layer of coding slips off just before delivery. 
• A baby weighing around one and a half pounds and ten inches long will be born in the fifth month.

Sixth month

When a baby reaches this stage of development, its reddish skin will show wrinkles and veins, and its translucent skin will display wrinkles and veins. There are even finger and toe prints visible at this stage of development. It is even possible to see that the eyelids are parted and the eyes are opening. 

• The baby is now about to move and will start to have a pulse when the sound is heard. In this case, you will actually be able to feel the jerking movements caused by the hiccups. 
• In the event of premature birth, the baby will be able to survive if delivered after the twenty-third week. 
• A baby weighing two pounds and standing 12 inches tall will be born at the end of the sixth month.

Seventh Month

It is during this time that the baby matures and develops body fat reserves. This is also the time when the body is fully developed in terms of hearing. Changes in position and responses to stimuli, including sound, pain, and light, are characteristic of the newborn. 

As the fetal fluid begins to diminish, this is called the dropping of the amniotic fluid.

•  A baby weighing two to four pounds at 14 inches long will be born after the seventh month of pregnancy. It is possible for premature babies to survive after the seventh month if they were born early.

Eighth month

Although the baby is still growing, he or she is still developing reserves of body fat. It will be easier to observe the baby now that he is kicking more. During this time, a baby's brain will expand rapidly and in addition to seeing and hearing, it will begin to develop its own abilities. The majority of the internal systems are well developed, with the exception of the lungs. The baby will weigh almost five pounds at this stage and be eighteen inches long.

Ninth Month

A baby's lungs are almost ready to open up at this point in time. During the first few weeks after birth, babies' reflexes are well coordinated so that they can close their eyes, blink, turn their heads, and grip firmly. 

• Upon hearing, seeing, or touching him or her, the brain will respond appropriately. This is the moment when we can say it's time to get the baby started in life. 
• When the baby reaches this stage, it moves less because of space constraints. It has now started positioning itself for birth. 
• Once they fall into the pelvis, the baby will be ready to be born. Its head will usually be pointed towards the birth canal at this point. 
• The baby will grow to approximately 18 to 20 inches long and weigh approximately seven pounds by the end of the month.

Fetus Growth throughut the months

Things to Remember

• The heart is the first organ to begin functioning. Development of the heart begins around the first month of pregnancy. 
• The 2nd month is when the legs and fingers develop. All major organ systems are fully developed by the end of the first trimester or the third month of pregnancy.
•  It is possible to see the reproductive organs. At the end of the 5th month, the embryo begins to move and hair begin to appear on its head. 
• The 2nd trimester (24 weeks or 6 months) is distinguished by the formation of eyelashes, eyelid separation, and the development of fine hair on the body. 
• The foetus is ready to give birth by the end of the ninth month.

Read more: Birth Delivery steps