Day 1 (conception or fertilization)
The egg (23 chromosomes) is fertilized by a sperm (23 chromosomes) and they form one cell (46 chromosomes) that at first is smaller than a grain of sugar. This one cell contains the plans for every detail of the baby’s development, including sex, hair and eye color, height, and skin tone.
New individual burrows into the wall of the womb.
The baby’s heart begins to beat.
Week 3 (1 week after fertilization)
The brain, spinal cord, and nervous system develop.
Week 8 (6 weeks after fertilization)
All body systems are present. The lungs are forming, brain waves are recorded, muscles work together, and reflexes are present.
Week 10 (8 weeks after fertilization)
The body is complete. Changes after this are primarily in size, rather than appearance.
Month 3 (10 weeks after fertilization)
The baby’s lung and brain growth are largely completed. The baby can hear, suck her thumb, and her fingers can grasp objects. Her fingerprints are already evident. The baby can even wrinkle her forehead!
Month 4 (14 weeks after fertilization)
At this age, the baby reacts to loud noises. Fingerprints which individualize each human being have now developed on the tiny fingers of the fetus.
By End of Month 4
The baby is 8 to 10 inches long and weighs a half-pound or more. The heart pumps 16 gallons of blood every day and the mother can now feel movement.
Months 5 and 6
The baby grows to be about 12 inches long. If born this early, she has a chance to survive outside the womb with medical intervention.
Months 7, 8 and 9
The baby uses the four senses of vision, hearing, taste and touch. The baby can recognize its mother’s voice. Eyelids open and close, eyes look around.
By End of Month 9
The baby normally weighs 6 to 9 pounds and is now ready for birth.