First Month
Day 1: Sperm joins with ovum (egg) to form one cell--smaller than a grain of salt. The new life has inherited 23 chromosomes from each parent, 46 in all. This one cell contains the complex genetic blueprint for every detail of human development--the child's sex, hair and eye color, height, skin tone.
Days 3-4: The fertilized egg travels down the fallopian tube into the uterus, where the lining has been prepared for implantation.
Days 5-9: During this time, the fertilized egg implants itself in the rich lining of the uterus and begins to draw nourishment.
Days 10-14: The developing embryo signals its presence through placental chemicals and hormones, preventing the mother from menstruating.
Day 20: Foundations of the brain, spinal cord and nervous system are already established.
Day 21: The heart begins to beat.
Day 28: The backbone and muscles are forming. Arms, legs, eyes and ears have begun to show.
At one month old, the embryo is 10,000 times larger than the original fertilized egg--and developing rapidly. The heart is pumping increasing quantities of blood through the circulatory system. The placenta forms a unique barrier that keeps the mother's blood separate while allowing food and oxygen to pass through to the embryo.
Second Month
Week 6: The liver is now taking over the production of blood cells, and the brain begins to control movement of muscles and organs. The mother is about to miss her second period and has probably confirmed that she is pregnant.
Week 7: The embryo begins to move spontaneously. The jaw forms, including teeth buds in the gums. Soon the eyelids will seal to protect the embryo's developing light-sensitive eyes, and will reopen at about the seventh month.
Week 8: At a little more than an inch long, the developing life is now called a fetus--Latin for "young one" or "offspring." Everything is now present that will be found in a fully developed adult. The heart has been beating for more than a month, the stomach produces digestive juices and the kidneys have begun to function. Forty muscle sets begin to operate in conjunction with the nervous system. The fetus' body responds to touch, although the mother will not be able to feel movement until the fourth or fifth month.
[Fetal Development Index] [Months One & Two] [Months Three & Four] [Months Five through Nine]