Articles
Fetal development: The first trimester
Week 5: Hormone levels increase
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
Content
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
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
Content
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
Week 3: Fertilization
The sperm and egg unite in one of the fallopian tubes to form a one-celled entity called a zygote. If more than one egg is released and fertilized, or if the fertilized egg splits into two, the result may be multiple zygotes and a twin pregnancy.
The zygote typically has 46 chromosomes. That includes 23 from each biological parent. The chromosomes help determine the baby's sex and physical traits.
Soon after fertilization, the zygote travels down the fallopian tube toward the uterus. At the same time, it begins dividing to form a cluster of cells called a morula. A morula looks like a tiny raspberry.
