Fetal development: The first trimester

6 月 14, 2026
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Weeks 1 and 2: Getting ready

Week 3: Fertilization

Week 4: Implantation

Week 5: Hormone levels rise

Week 6: The neural tube closes

Week 7: The head develops

Week 8: The nose forms

Week 9: Toes appear

Week 10: The elbows bend

Week 11: Genitals develop

Week 12: Fingernails form

Updated: March 18, 2025

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© 2026 Mayo Foundation for Medical Education and Research (MFMER). All rights reserved.