How Life Begins
The extraordinary 9-month transformation from a single cell to a fully formed human being
Week 1-2: The Miracle of Conception
Life begins when a sperm cell successfully penetrates the egg in the fallopian tube. This single fertilized cell, called a zygote, contains all the genetic information needed to create a unique human being.
Key Developments:
- • Zygote begins rapid cell division (cleavage)
- • Travels down fallopian tube toward uterus
- • By day 5, becomes a blastocyst ready for implantation
The Three Trimesters of Pregnancy
1 First Trimester (Weeks 1-12)
The most rapid period of development as the embryo forms all major organs and body systems.
2 Second Trimester (Weeks 13-26)
The fetus grows dramatically in size and begins practicing life outside the womb.
3 Third Trimester (Weeks 27-40)
Final preparations for birth as the fetus gains weight and refines systems.
Key Developmental Milestones
Month 1
The neural tube forms, which will become the brain and spinal cord. The heart begins to beat by the end of the first month.
Size: ~1/4 inch (6mm)
Size: ~2.5 inches (6cm)
Month 3
All major organs are formed. Fingers and toes are distinct. The fetus can make tiny movements, though the mother can't feel them yet.
Month 6
Eyebrows and eyelashes form. The fetus can hear sounds and respond to them. The lungs begin to develop surfactant for breathing.
Size: ~12 inches (30cm)
Size: ~18-20 inches (45-50cm)
Month 9
The brain continues rapid development. The fetus gains about 1/2 pound per week. Most babies turn head-down in preparation for birth.
Interactive Exploration
Track the Baby's Growth Week by Week
About the size of a banana
Week 20 Developments
- • Baby is covered in vernix caseosa, a protective coating
- • Can hear and recognize mother's voice
- • Developing taste buds
The Miracle of Birth
After approximately 40 weeks of incredible development, the baby is ready to enter the world. The average newborn weighs about 7.5 pounds (3.4 kg) and measures 20 inches (51 cm) long. But the journey of growth has only just begun!