Articles
Fetal development: The 1st trimester
Content
Weeks 1 and 2: Getting ready
Week 3: Fertilization
Week 4: Implantation
Week 5: Hormone levels increase
Week 6: The neural tube closes
Week 7: Baby's head develops
Week 8: Baby's nose forms
Week 9: Baby's toes appear
Week 10: Baby's elbows bend
Week 11: Baby's genitals develop
Week 12: Baby's fingernails form
Week 4: Implantation
The rapidly dividing ball of cells — now known as a blastocyst — has begun to burrow into the uterine lining (endometrium). This process is called implantation.
Within the blastocyst, the inner group of cells will become the embryo. The outer layer will give rise to part of the placenta, which will nourish your baby throughout the pregnancy.
