Title: Prenatal Development | Lifespan Development
Headings: 
Prenatal Development
Learning Outcomes
Periods of Prenatal Development
The Germinal Period (Weeks 1-2)
The Embryonic Period (Weeks 3-8)
The Fetal Period (Weeks 9-40)
Watch It
Try It
Glossary
Contribute!

Content: The Fetal Period (Weeks 9-40)
Figure 3. A fetus at 10 weeks of development. When the organism is about nine weeks old, the embryo is called a fetus. At this stage, the fetus is about the size of a kidney bean and begins to take on the recognizable form of a human being as the “tail” begins to disappear. From 9–12 weeks, the sex organs begin to differentiate. By the 12th week, the fetus has all its body parts including external genitalia. In the following weeks, the fetus will develop hair, nails, teeth and the excretory and digestive systems will continue to develop. At the end of the 12th week, the fetus is about 3 inches long and weighs about 28 grams. At about 16 weeks, the fetus is approximately 4.5 inches long. Fingers and toes are fully developed, and fingerprints are visible.