Title: Fetal Development in the First Trimester: Stages & Timeline - Video & Lesson Transcript | Study.com
Headings: Fetal Development in the First Trimester: Stages & Timeline
Fetal Development in the First Trimester: Stages & Timeline
Lesson Transcript
Embryogenesis
Cell Differentiation
Organogenesis
1st Trimester: Weeks 0-4
1st Trimester: Weeks 5-8
Register to view this lesson
Are you a student or a teacher?
Fetal Development in the First Trimester: Stages & Timeline
Start today. Try it now
Fetal Development in the First Trimester: Stages & Timeline
Related Study Materials
Explore our library of over 84,000 lessons

Content: Weeks 9-12
Until now, the growing being inside the woman's uterus has been referred to as an embryo. But at month 3, the embryo is now officially called a fetus, all the way up until month 9 when it is born. As the embryo enters the realm of fetushood (okay, that's probably not a real word, but you get my point), the limb buds from month 2 have continued to grow and even show signs of webbed fingers and toes as we head into month 3. These will form individual fingers and toes and even have nails by the end of the first trimester. Not only that, but the eyes have developed and most of the major organ systems are in the beginning stages of growth and function. The kidneys, brain, liver and intestines are all starting to function, and there is even the detection of brain waves between weeks 8 and 9. At month three, the embryo is called a fetus and major organ systems begin to develop

By the end of month 3, the fetus is about the size of a plum, still a little alien in appearance, but by this time, it has 90% of the organs, tissues, muscles and other body parts found in adults. Now, even though most of these systems are formed, they still need to grow in size and each system needs to be refined before it can fully function on its own. Lesson Summary
That growth and refinement will take place over the next 2 trimesters, or 6 months. Over the next 6 months, the fetus with grow rapidly, increasing in size by 1500%, give or take a few ounces.