Difference Between Embryo and Fetus (With Table)

Humans go through different stages as they evolve into their better and newer versions according to the time and transitions required. And those differences would be relatively visible to see as well.

Yet it is a quite fascinating fact that humans don’t grow only after entering into the world, they have started growing and evolving into different phases right after conception. Yes, their development of body would begin getting into transitions since their existence in their mother’s womb.

And as such phases involve the terms of Embryo and Fetus in the uterus. Both occur at different times yet with much unique importance to their stages.

Embryo vs Fetus

The main difference between Embryo and Fetus is that the Embryo’s development occurs earlier in the process of the phases based on the gestational stage, on the other hand, the Fetus begins its phase following the development of the embryo after conception.

Embryo vs Fetus

An embryo is considered to be the beginning phase of human development after conception. During the stage of embryo, most organs are structured to form into shapes. It is the most critical and vulnerable level of pregnancy, for miscarriages and birth defects are common around that time.

The fetus is the developed stage of the embryo, growing into a baby. The vital organs formed during the embryonic period would further grow at this stage. Also, the organs would gradually start to function when the baby is a fetus, a step of preparing the baby to survive the outside world.

Comparison Table Between Embryo and Fetus

Parameters of ComparisonEmbryoFetus
DefinitionAn embryo is an early form of human or any organism development.A fetus is an advanced form of an embryo.
Period of PhaseThe embryonic period starts from the 3rd week and lasts till the 8th week after conception.The fetal stage begins from the 9th week until the birth of the baby
CharacteristicsThe cells of the embryo would grow and develop the vital organs during the embryonic period.The crucial organs would expand further into the form of a baby. And the functions of the organs would be more prominent during the fetal development stage.
ShapeThe embryo has the shape of an oval disc.The fetus has a circular shape with limbs, arms and other organs formed.
SizeThe size of an embryo around 8 weeks would be 0.6 inches. Pea like size.Ranging from the initial weeks of the fetus to the final week of the pregnancy, the fetus would have the size of 1.22 inches to 20.39 inches.

What is an Embryo?

The embryo is the term directed toward the developing unborn baby residing in the uterus of the mother. It is an important stage, owing to reasons like vulnerability to birth defects and more common miscarriages.  

Yet another characteristic that makes the embryonic stage the more crucial is the formation of organs. The heart is formed along with its main blood vessels during this developmental stage. The embryo is highly sensitive to the harmful impacts of drugs, radiation and any viral infection.

During the initial stage, embryo is framed into three layers, namely ectoderm, mesoderm and endoderm. The endoderm is the top layer that will eventually turn into the skin, nervous system, eyes, inner eyes and connective tissues.

The mesoderm is the middle layer, and it would take responsibility for the development of the bones, kidneys, muscles and reproductive system. And ectoderm is the last layer with the lungs, intestines and bladder development.

By the 6th week of pregnancy, the heart would start beating and the embryo would elongate the organs to resemble humans. The primitive brain and neural tube also grow to shape. Sooner, by the end of the embryonic phase, the entire baby organs are shaped into a form, mainly including the arms, legs and limbs.

The brain and spinal cord are still developing by the final weeks of embryonic stage and will continue to do so throughout pregnancy. When the embryonic period would come to an end, the baby, that is, the embryo would be around 2 inches long.

What is a Fetus?

The fetus is regarded as the advanced form of the embryo as its stage begins at the end of the embryonic phase. Fetal development majorly involves the functions of the organs grown during the earlier embryonic stage.

During fetal development, the gender of the fetus can be identified. The mother would start feeling the movements of the fetus inside the womb, as the limbs are grown and developed during the fetal stage.

The fetus would start growing fingernails with the facial features coming close to look like a human. So, by the end of the first trimester, the baby would be around 2½ inches long.

The second trimester would mark the baby’s further growth like the development of sex organs, hair tissues that are visible, the strength of the bones would be increasing, the fats are gaining on the body. Crossing the midway of this trimester, the fetus would be able to hear the voices. They gain the ability to suck and swallow. The fetus would range the growth of 9 inches.

By the third trimester, the baby would be grown to resemble a newborn size. And now, the fetus can open its eyes and implement to breathe in the amniotic fluid around it. And 20 inches would be the approximate inches of the fetus in this stage. After childbirth, the height and weight of the baby would vary accordingly.

Main Differences Between Embryo and Fetus

  1.  After conception, the development of an embryo and a fetus occur at two different periods of time.
  2. The duration of the embryonic phase is for 7-8 weeks, while the duration of fetal development tends to last longer, for about 30 weeks.
  3. Despite the shorter interval of embryonic stage, in comparison with fetal development, it carries the importance for developing the vital organs.
  4. Embryonic stage is especially known for its vulnerability to drugs, infections and radiation.
  5. Fetal stage embarks the functions of the organs developed in the embryonic phase.
  6. A comparatively larger number of miscarriages happen during the growth of the embryo.


It is evident how mesmerizing it is to comprehend the working of embryo and fetus, apparently, the science behind it leaves us stunned most of the times with the facts. The growth of humans appears so natural, almost like a normal occurrence that happens on daily basis. On the contrary, this development that humans evolve themselves into is anything but normal.

Each milestone carries significance, from embryo to fetus, there is a huge transition that occurs. If not because of this evolution, humans or any organisms would be inevitably incomplete. The journey from the embryo to fetus is completed as humans are born, but that shouldn’t deter the growth humans would attain as they evolve in the later life. The expansion would keep on increasing, so should the humans.


  1. https://link.springer.com/chapter/10.1007/978-3-642-69302-1_8
  2. https://europepmc.org/article/med/1010389