Title: First Trimester of Pregnancy | American Pregnancy Association
Headings: Fetal Development: First Trimester
Fetal Development: First Trimester
The First Trimester of Pregnancy
Week 1 & 2 – Gestational Age
Week 3 – Gestational Age (Fetal Development – Week 1)
Week 4 & 5 – Gestational Age (Fetal Development – Weeks 2 & 3)
Week 6 – Gestational Age (Fetal Development – Week 4)
Week 7 – Gestational Age (Fetal Development – Week 5)
Week 8 – Gestational Age (Fetal Development – Week 6)
Weeks 9 thru 13 – Gestational Age (Fetal Development – Weeks 7 thru 11)
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Content: Week 3 – Gestational Age (Fetal Development – Week 1)
The embryo is going through a lot of basic growth at this time, with the beginning development of the brain, spinal cord, heart, and gastrointestinal tract. Week 4 & 5 – Gestational Age (Fetal Development – Weeks 2 & 3)
Arm and leg buds are visible, but not clearly distinguishable. The heart is now beating at a steady rhythm. The placenta has begun to form and is producing some important hormones including hCG. There is a movement of rudimentary blood through the main vessels. The early structures that will become the eyes and ears are forming. The embryo is a ¼ inch long by the end of these weeks. Week 6 – Gestational Age (Fetal Development – Week 4)
The formation of the lungs, jaw, nose, and palate begin now. The hand and feet buds have webbed structures that will become the fingers and toes. The brain is continuing to form into its complex parts.