Everything you need to know about embryo development and the stages of embryo development!

Introduction to Embryo Development 

What is Embryo Development?

From the day a woman gets pregnant till the day she gives birth to a baby, many procedures take place inside her Uterus. Within ten months from the date of pregnancy, a new life starts evolving and finally coming out of the mother’s womb. The whole procedure is known as Embryo development. Whether the process generally occurs inside a woman’s womb or in a lab, the day-to-day development process of the embryo is magical. 

What are the Stages of Embryo?

 There are five stages of an embryo that can be seen through this process. The stages are; 

  1. Fertilization
  2. Blastocyst development
  3. Blastocyst implantation
  4. Embryo development
  5. Fetal development

Now let’s understand these processes in details:

Fertilization: The phase where the male sperm fertilizes or combines with the female egg. This process takes place inside the female reproductive system. A woman ovulates appropriately once a month. During the ovulation, the woman releases one or two eggs, and the gamete is released inside the fallopian tube. The woman also releases cervical mucus to let the male sperm enter her vagina quickly and without much effort. After successful intercourse, the sperm swims through the cervix towards the uterine tube. Here within 24 to 72 hours, the fertilization takes place. The Zygote then moves more towards the Uterus for the next step. 

Blastocyst Development: In this stage, there is an egg-like structure where inner and outer cells are present with lots of fluids. During this stage, the embryo starts developing into a tight human structure. The outer cells are called zona pellucida, almost equal to egg cells that give protection and support to the structure. The inner cells will convert into the skin, heart, muscles, liver, and other parts of the body. This development stage stays for a short time, and it works very fast. The development takes place within 9-10 days after the fertilization. Finally, the zona pellucida walls get dissolved, and the blastocyst starts moving towards the Uterus for further steps. 

Blastocyst Implantation: Finally, the blastocyst gets implanted at the Endometrium, and the outer lining of this layer and the outer lining of the blastocyst creates placenta. This connection helps the embryo to get all the nutrients from the mother’s body and to move out the wastes from the embryo. 

Embryo development: This is the stage where the blastocyst finally converts into an embryo. The outer line of the blastocyst converts into the skin. The heart tubes get formed, first bones start to grow from the cartilage, etc. The blastocyst finally gets a shape, and within the ten to twelve weeks of pregnancy, finally, the structure of the fetus can be seen, including the blood circulation. 

Fetal Development: All the organs have grown by now, but the maturity is still in process. Three months after pregnancy, the fetus length is around 5 inches. At six months, its length is around 12 inches, and it starts responding to different sounds. At months 8 and 9, all the developments are done, and the brain starts proliferating to give the body a perfect shape. 

3. Developments with each problem: The whole embryo development process occurs for ten months of a woman’s pregnancy. If at any stage of the development a particular problem is seen, that can hamper the whole thing. Here are the problems with each step of embryo development. 

Problems during Fertilization: The sperm cannot reach the egg, and the fertilization process doesn’t occur. Sometimes the sperm cannot penetrate, it cannot move through the egg, or it cannot fertilize it for different reasons. But the result is the same for every reason. 

Problems during Blastocyst development: Blastocyst arrest occurs, and the cells cannot divide into two. The further development procedure stops here. 

Problems during Blastocyst implantation: Sometimes, the fertilized egg cannot get placed inside the Uterus. Sometimes it fails to develop due to some problems inside the sperm chromosomes. In both cases, the further procedure stops. This thing happens in the early days of pregnancy. 

Problems during Embryo development: Many developments take place inside the embryo at this stage. Any genetic abnormality can result in severe damage to the developing organs. This happens within three weeks of pregnancy. 

Problems during Fetal development: At this stage, miscarriages do not take place. But exposure to a toxic environment can result in congenital malfunctions or physiological abnormalities. 

4. Embryo Development Day by Day: The Embryo development process is a beautiful experience, and it doesn’t happen within a day or so. It takes time to develop the embryo. 

Day 1-3: This is called the cleavage stage, where the Zygote doesn’t grow faster. One single cell will divide into several cells, and genetic information starts replicated in them. 

Day 3-5: This is called the Morula stage, where the Zygote finally starts developing. Now 16 cells are there, forming a circle inside the woman’s womb. 

Day 5: The Blastocyst stage starts from this day. This is the final stage where the Zygote can develop. Here, two hollow circles are created where all the cells are placed. The outer circle creates the skin and the outer parts of the body, where the inner circle creates the organelles. At this stage, the Zygote finally converts into an embryo and then eventually into a fetus.   

5. Other Developments in the Embryo – Week 5, 6, 7 & 8: After fertilization, all developments are essential. Every week the embryo starts developing quickly. 

Week 5: Here, the embryo length is around 4 mm, and it starts converting into a C shape. Face, neck, inner ears, arm buds start to form in this stage. The liver, gallbladder, spleen, and Pancreas also start to form. 

Week 6: Now, the embryo length is around 8mm. The nose and eyes start to develop at this stage. The legs are starting to form along with the kidney and liver. 

Week 7: Now, the embryo length is around 13 mm. Now the lungs start forming, and the prenatal sex organs also start forming. 

Week 8: External ears, nipple, hair follicles will start forming at this stage. Fetal heartbeat and limb movement can be seen through ultrasound now. Finally, a human face starts to form at this stage. 

6. Path to improved health: Development of the embryo in the Embryo development stage is the mainframe of a human being’s existence. All the major organs start developing at this stage, and the brain also starts forming. A small mistake in the process, and the whole life of the baby gets devastated. This is the reason it is called the path to improved health. Embryo development is the most essential and sensitive phase of a baby’s life. At any phase, miscarriages take place due to several reasons. So, the time between the 5th and the 10th week of pregnancy is crucial and sensitive. 

7. Understanding embryo grading: Embryo grading is a medical process where fertility experts choose one or more embryos to transfer in the womb. Generally, not all embryos are healthy enough to bring a pregnancy to you. In most cases,  a healthy embryo gets transferred on the 3rd or 5th day after the retrieval. But sometimes, for unknown reasons, poor-grade embryos work wonderfully and surprisingly better than the healthiest embryos. No matter how experienced the embryologist is, sometimes, the experience doesn’t work for him. Grading is a tool that helps embryologists to decide which embryos should be transferred and how many embryos should be transferred. Many other factors are also considered here, like her health, family history, pregnancy history, etc. 


Is a woman responsible for infertility? 

Ans: Doctors determine the fertility potential depending on the total contribution of two partners. So, the woman is not always at fault. The male counterpart is equally responsible, and he can be infertile too! Male infertility is as common as the woman one. A doctor and some tests can clear the confusion. 

When a couple needs IVF? 

Ans: IVF or In vitro fertilization is the process of bringing a new life to your house. This is a medical procedure that requires time and lots of other specifications. When a couple faces problems like impaired sperm production, premature ovarian failure, unexplained infertility, fallopian tube damage, etc., the couple is prescribed IVF. 

Can the test damage the embryo? 

Ans: Testing can never harm the embryo until you do the procedure as per the required time. The doctor can take out one or several cells on the exact date. If such precautions are taken initially, the test won’t harm embryos at all! 

During the IVF cycle, how many embryos are transferred? 

Ans: Generally, these testing centers and hospitals try to offer a painless procedure, and in most cases, the result is definite and positive. So, on the safer side, the doctor transfers two embryos to your womb.

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