Embryo vs. Fetus

What is the difference between embryo and fetus? As a baby develops in the womb, it goes through…

What is the difference between embryo and fetus?

As a baby develops in the womb, it goes through different stages. Two of these are embryo and fetus. Human life starts at conception, which is when the sperm fertilizes the egg in the Fallopian tube. This ovum then starts to grow and the cells start to divide. When the cells divide to form two, which occurs in the first eight weeks, this period of gestation is called the embryonic period and the resulting divided cell growth is known as the embryo.

The embryo starts to grow and divide at a very fast pace. This stage of development is a critical one because the embryo forms in the Fallopian tube and slowly makes its way into the womb. There it becomes implanted in the lining of the uterus. In some cases the embryo does not move out of the Fallopian tube properly and it remains there. This is called an ectopic pregnancy and it is a serious situation that could be fatal for the mother. When this happens the pregnancy has to be terminated.

Once the embryo is implanted in the wall of the uterus, it starts to grow and develop and the placenta forms to provide the nourishment that it needs. Taking prescription medication and illegal drugs can be harmful to the embryo because this is the stage during which the organs develop.  Drugs that are harmful to take in the embryonic stage are called Teratogenic drugs. Some examples are high doses of Vitamin A and medication for hypertension.

The fetal period starts at the ninth week of pregnancy and is characterized by the rapid growth of the organs of the body. This growth depends on certain factors, such as the amount of room in the uterus and the blood supply in the placenta. If either of these factors is compromised the result could be low birth weight as a result of intra-uterine growth retardation (IUGR).


  1. A baby in the womb is either an embryo or a fetus.
  2. The embryonic stage is the first 8 weeks of pregnancy and is the time in which the organs develop.
  3. The fetal stage starts at the 9th week of pregnancy and is characterized by rapid growth of the baby.
  4. Drugs may be harmful to the embryo.


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