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: 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. During the 4-6th months, the eyes become more sensitive to light and hearing develops. The respiratory system continues to develop. Reflexes such as sucking, swallowing and hiccuping develop during the 5th month. Cycles of sleep and wakefulness are present at that time as well. Throughout the fetal stage, the brain continues to grow and develop, nearly doubling in size from weeks 16 to 28.