Difference Between Embryo and Fetus

Humans are a different and confusing species. Many things about them are difficult or, in some cases, impossible to understand. But understanding their body or biological function is not among them.

Humans, like any other animals, undergo fertilization to produce the next generation. It is not something that needs to be done but still due to sentimental or religious or any reason they like to extend their family.

Now when a woman gives birth to a child, several changes in their body take place during the pregnancy period.

Embryo and fetus are two terms that are linked with pregnancy. Both of them are similar and yet can be difficult to differentiate.

Embryo vs Fetus

The main difference between embryo and fetus is in the stage they develop. Embryo takes place earlier than fetus during the initial weeks of the pregnancy after conception through the process of cell division, whereas after the full development of embryo fetus is developed from it during the midweeks and remain till the end of 9th month of the pregnancy. Compared to an embryo, a fetus can be easily felt without the help of ultrasound. This may be due to the reason it is bigger in size, which can vary from 4 to 7 inches, while the embryo is felt with the help of ultrasound as it is smaller than the fetus. Another important difference between them is an embryo is unicellular (i.e., made up of one cell) while the fetus is multi-cellular (i.e., made up of more than one cell).

Embryo vs Fetus

The embryo is the stage of pregnancy takes place during the 2 to 3 week, during with the body of the baby start forming. It is developed through the cell division process after conception.

It takes place till the 10th or 13th week of the pregnancy. Ultrasound is used for seeing or feeling the presence of it as it is small in size. It is formed with one cell, and therefore it is unicellular.

The fetus is the stage that takes place after the 8th week of conception, and it is developed from the embryos. It lasts for more weeks than embryos during with the body parts of the baby starting growing and developing.

This stage is easily visible to everyone due to the bigger size of the fetus. It is made up of more than one cell and therefore is multi-cellular.

Comparison Table Between Embryo and Fetus

Parameters of ComparisonEmbryoFetus
DevelopedAfter conceptionFrom embryos
Age10 to 13 weeksFrom 9th week till birth
PresenceIt can be felt with the help of ultrasoundsIt can be felt easily after 21 weeks
FormedThrough the cell division processGrowth and development of an embryo

What is Embryo?

It is the first stage of the development of the zygote, during which the fertilized egg undergoes a cell division process. Embryonic development includes the following stages:

  1. Blastula stage: in this stage, the blastocoels are formed and get enclosed with the sheet cell called blastomeres.
  2. Gastrula Stage: this stage is responsible for the division and migration of cells.
  3. Organogenesis Stage: this stage is responsible for the development of the organs of the baby.

After this, the development of the spinal cord and heartbeat is displayed that can be felt with the ultrasounds. This is stage is very important as any Negligence can result in a lifetime problem.

For example, most of the disabilities in a child takes place during this stage that cannot be treated afterward.

This stage only lasts for a couple of weeks but plays an important role in the body’s functional development of the baby by developing the organs and tissues.

The process of developing the embryos is also called embryogenesis. It starts after 4-5 days of fertilization.

What is Fetus?

A fully developed embryo then turns into a fetus after the 9th or 10th week of fertilization. This is the longest stage that lasts till the baby is born.

As mentioned above, the body organs along with tissues start developing in the embryo, but in the fetus, the main body parts such as hands, legs, head start developing and get a proper shape of a human.

Also, the organs that developed during embryo development are not properly located. That is done is a fetus.

External genitalia is clearly visible in the baby and can be seen with the help of ultrasounds during this stage.

During the initial stage of the fetus, the size of the head is bigger in comparison, but in late stages, it becomes proportionate to the size of the body. And the growth of the body continues during the period.

If proper care is not taken, the part of the body of the baby can grow differently or can cause some sort of disability as well. Proper nutrition and health care are required during this stage to make sure the baby is developed fully.

Main Differences Between Embryo and Fetus

  1. The major difference between both embryo and fetus is when they are developed. The embryo is early stage and therefore is developed after the conception, whereas the fetus takes place after the embryo stage or it is developed from the embryo.
  2. Age of embryo is comparatively less, as it only exists from 10 to 13 weeks whereas fetus takes place after completion of embryo stages, i.e., 10 to 13 weeks, and remains till the time of birth, meaning its age is relatively longer.
  3. As an embryo take place during the initial weeks of the pregnancy and presence of it is impossible to feel with hand, it can only be felt with the help of ultrasound while the fetus takes place till the end weeks of the pregnancy and hence the presence of it is easier to be felt.
  4. Embryo further involves several other stages, for example, germinal, fertilization, implantation, gastrulation, blastulation, etc. all of these are involved in the formation of the embryo while the fetus is further developed from the fully developed embryo; hence no such stages are involved in the formation of it.
  5. The basic structure of the body of the offspring or baby takes place during the embryonic period of the pregnancy while the body and parts of it further are developed and grow during the fetal period of the pregnancy.
  6. Lastly, both of them differ in terms of their size. In the initial stage of the embryo, the size of it can vary from 3-4mm, whereas the fetus is large than that. The minimum size of it is 4 inches, while the maximum can go to 8 inches.
Difference Between Embryo and Fetus


Therefore with the help of the above information, it is not difficult to differentiate between both of them. These two stages are involved in the development of a baby. Because of their similarities, they are used interchangeably by people.

Although it is not very much important to understand the difference, for a pregnant woman, it is quite important to know the different stages of the pregnancy to take proper care along with all necessary precautions.

These stages take place after the conception by women; during these stages, a child develops organs and full body parts. There can be some complications during pregnancy that might take place during these stages.

Therefore, it is important to always seek professional help.


  1. https://www.publish.csiro.au/rd/rd06130
  2. https://www.sciencedirect.com/science/article/pii/S0093691X99002642
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