Difference Between Embryo and Fetus

The key difference between embryo and fetus is that the embryo is the term that describes the development of a young offspring in mothers’ womb from the day of fertilization to end of the eighth week of gestation while the fetus is the term that describes embryo from the eighth week onwards until the offspring is born.

Fertilization refers to the process where an egg cell unites with a sperm cell to form a diploid zygote during sexual reproduction. Consequently, the development of a young offspring takes place from the day of fertilization until the day of birth inside the mother’s womb. Upon the formation of zygote, it undergoes different stages of cell division. Likewise, embryo and fetus are two stages of the pregnancy.

CONTENTS

1. Overview and Key Difference
2. What is an Embryo
3. What is a Fetus
4. Similarities Between Embryo and Fetus
5. Side by Side Comparison – Embryo vs Fetus in Tabular Form
6. Summary

What is an Embryo?

The embryo is the first stage of development of the zygote. The zygote is a diploid cell where the egg unites with a sperm. Then the fertilized egg undergoes rapid cell division process during the initial phase of embryonic development. Here, the embryo’s cells multiply and differentiate to take on various functions. Furthermore, there are three main stages in the embryonic development namely blastula, gastrula and organogenesis stage.

Blastocoels form and enclose with a sheet of cells called blastomeres during the blastula stage. On the other hand, division and migration of cells occur during the gastrula stage. Finally, during the organogenesis stage, internal organs start to develop through a series of processes. By the 5^th week of development, a heartbeat is displayed. A neural tube is formed, and it gets developed into the brain and the spinal cord during this stage of development.

In addition, the embryonic stage is an important and crucial development stage since the developing offspring is prone to risks that could develop congenital disabilities.

What is a Fetus?

A fetus is the term that describes the embryo development from the 9th week of fertilization till delivery of the baby. During this period of development, the embryo takes on a more human form. The major body organs such as liver brain and kidneys are present in the fetal stage. But these organs aren’t fully developed or in their correct anatomical location. The size of the head of the fetus is larger in comparison to the body. The fetus is usually 30 millimetres long from crown to rump. The head makes half of the length of the fetal body. At this stage, the fetus weighs around 08 grams.

The lungs start to develop and brain hand, feet and other organs are present with minimal function. Also, during this stage, external genitalia are present and visible to the ultrasound. During the later stages of fetal development, the size of the head gets proportionate to the size of the body. Furthermore, the growth of the organs rapidly occurs during the period. The growth depends on the placental blood supply, the available space in the uterine cavity and the maternal nutritional status.

What are the Similarities Between Embryo and Fetus?

• Embryo and the fetus are two stages of the development of an offspring once the zygote is formed.
• During both stages, important developmental procedures take place under rapid cell division.

What is the Difference Between Embryo and Fetus?

Both embryo and fetus are the intra uterine babies. The embryo is the early stage of the intra uterine baby while the fetus is the intra uterine baby, from the 9^th week of fertilization till delivery of the baby. Therefore, we can consider this as the key difference between embryo and fetus. During the embryo period, organs start to form while during the fetal period organs grow rapidly. Hence, this is also a difference between embryo and fetus.

Summary – Embryo vs Fetus

Embryo and fetus are two stages of the development of an offspring once the zygote is formed. The embryo is the first stage of development of the zygote. The period of embryonic development could be divided into three main stages; blastula, gastrula and organogenesis stage. Embryo exists till the eighth week of the fertilization. On the other hand, fetus is the term that refers the embryo development from the eighth week of fertilization until the birth of the offspring. The growth of the organs rapidly occurs during this period. However, during both stages, important developmental procedures take place under rapid cell division. So, this is the summary of the difference between embryo and fetus.

Reference:

1.Study.com, Study.com. Available here 
2. Boundless. “Boundless Anatomy and Physiology.” Lumen Learning, Lumen. Available here 

Image Courtesy:

1.”548063929″ by Ed Uthman (CC BY 2.0) via Flickr
2.”Views of a Foetus in the Womb detail”By Leonardo da Vinci (Public Domain) via Commons Wikimedia