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13.67: Fetus Growth and Development

Difficulty Level: At Grade Created by: CK-12
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What characterizes this fetus as human?

The human fetus. Notice the details in the face and hands. Compare this to the human embryo, and the amount of growth and development is truly remarkable.

Growth and Development of the Fetus

From the end of the eighth week until birth, the developing organism is referred to as a fetus. Birth typically occurs at about 38 weeks after fertilization, so the fetal period generally lasts about 30 weeks. During this time, as outlined in Figure below, the organs complete their development. The fetus also grows rapidly in length and weight.

For detailed videos of growth and development of the fetus birth, go to these links: http://www.youtube.com/watch?v=aR-Qa_LD2m4&#38;feature=related and http://www.youtube.com/watch?v=RS1ti23SUSw&feature=related.

Fetus at 18 weeks after fertilization.

Fetal Development (Weeks 9–38). Organ development is completed and body size increases dramatically during weeks 9–38.

By the 38th week, the fetus is fully developed and ready to be born (see Figure below). A 38-week fetus normally ranges from 36 to 51 centimeters (14–20 inches) in length and weighs between 2.7 and 4.6 kilograms (about 6–10 pounds).

A 38-week-old fetus has completed development and will soon be born.


  • The fetal stage begins about two months after fertilization and continues until birth.
  • During this stage, organs continue to develop, and the fetus grows in size.


Use this resource to answer the questions that follow.

  • http://www.hippocampus.org/Biology \begin{align*}\rightarrow\end{align*} Biology for AP* \begin{align*}\rightarrow\end{align*} Search: Human Development
  1. What four membranes develop early on in the embryo? Describe their roles.
  2. What are the three germ layers?
  3. What is a fetus?
  4. Describe the role of the placenta.
  5. Describe fetal changes during the first, second and third trimesters of pregnancy.


1. Make a flow chart of embryonic and fetal development.

2. Why would an embryo be more susceptible than a fetus to damage by toxins?

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Developing human organism between weeks 8 and 38 after fertilization.

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Difficulty Level:
At Grade
Date Created:
Feb 24, 2012
Last Modified:
Aug 28, 2016
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