Embryo vs. Fetus: The Miracle of Life

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Difference between Embryo and Fetus

Human life! It doesn't get any better than this. Magically, a couple of cells get together and just know exactly what to do to create life, our progeny, the promise of our ancestors. After the embryo and fetus stages and a long process of gestation taking up to 9 months for humans, the miracle of birth happens. Until the magical moment of birth, there are several distinct stages of development to be met. Each one comes with its own physical transformations having specific roles in building up the complicated structure of the human body. All of these changes should be monitored by a doctor to ensure the baby is healthy, progressing normally and to be able to detect anything unusual prior to the culmination of the natural birth process.



An embryo is an organism in the development stage between fertilization and the physical body eight weeks afterwards. The embryo grows in the mother’s uterus or fallopian tube and implants into the uterine lining and establishes a feeding channel known as the umbilical cord. The embryo begins as a heart, then the tongue is developed and so on until it develops around an axis which will later become the spinal cord. In this period the brain, spine and gastrointestinal tract take shape and begin to evolve. The heart beat can be heard and seen on advanced medical equipment from this early stage. In weeks 4 and 5, body extensions are noticeable. These will grow to be the hands and the feet of the baby.

In weeks 6 to 8, the embryo will show signs of movement. The eyes start to form. Hair and facial features appear and develop. A fetus is a developing organism having surpassed the embryonic stage when it then begins preparing for birth. This occurs around the 9th week after fertilization.  The fetus then begins to develop a breathing movement necessary for lungs to start functioning. As a result of muscle and brain shaping activity, some uncontrolled twitching can occur.

Body Dimensions

An embryo at 4 weeks after fertilization may measure 0.2 inches in length. A fetus after 8 weeks of fertilization is about 1.25 inches in length. In the embryonic stage, many organs and functions begin to develop so the body is smaller and has a form subjected to many changes. In the fetal stage, the body begins to grow and further develops until it reaches up to 21 inches at birth.


A viable fetus is one that progresses normally in development. An embryo that does not show promise by way of cell multiplication can be said to be not viable. In other words, it looks as though it may not survive until the fetus stage or may develop too slowly or become abnormal in some way.

A fetus is most viable when it develops normally for 40 weeks. Most functions are fully developed and the fetus is said to be viable if born after 35 weeks. It is generally accepted that a fetus will be viable in 90% of cases if he is born after 26 to 27 weeks of gestation, the percentage drops considerably if birth occurs sooner.

Similarities and Differences

  • The embryo is procreation in the first development stage. After this, it passes to the fetus stage which culminates in child birth.
  • An embryo is identifiable at 4 to 5 weeks after gestation, while the fetus is identified at 6 to 8 weeks.
  • Embryo is defined by its size and age. The fetus is simply the next stage on the road to human life. 


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