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 ("zygote") travels down the fallopian tube into the uterus, where the lining has been prepared for implantation.

Days 5-9: The zygote implants itself in the rich lining of the uterus and begins to draw nourishment.

Days 10-14: The developing embryo signals its presence in the mother's body through chemicals and hormones, preventing the mother from menstruating.

Now attached to the wall of its mother's uterus, the former zygote is considered an "embryo."

The heart is formed at 20 days and beats at three weeks. From then on it will set the rhythm of life for this small kernel of humanity.

Foundations of the brain, spinal cord, and nervous system are already established.

Day 28: The backbone and muscles are forming. Arms, legs, eyes, and ears have begun to grow.

Day 30: 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.

Now the four primitive limb buds appear, first the arms, then the legs. Five fingers can be discerned in the hand.

At this stage toxic substances such as Thalomide may alter or hinder limb development despite the highly-protective placenta.

The head, disproportionately large at this time, is flexed on the rest of the body, about a quarter inch over all. The eyes darken as pigment is produced.

The umbilical cord joins the embryo to the placenta and to the yolk sac, which manufactures blood cells during the first weeks of the embryo’s life.

The front of the primitive neural tube is enlarged into three parts that very soon will become five: it is the future brain.

Brain waves can be detected and recorded with an electroencephalogram.

The end of a human life can be defined as the cessation of brain waves, but many ignore the scientific evidence of brain waves in unborn babies.

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.

The embryo begins to move spontaneously.

The jaw forms, including teeth buds in the gums.

Soon eyelids will seal to protect the embryo's developing light-sensitive eyes, and will reopen about the seventh month.

At a little more than an inch long, the developing life is now a fetus – Latin for “young one”.

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 baby’s body responds to touch, although the mother will not be able to feel movement until the fourth or fifth month.

Fingerprints are already evident in the skin. The baby will curve his fingers around an object placed in the palm of his hand.

The uterus is now doubled in size. The baby can now squint, swallow, and wrinkle his forehead.

The baby is now about 12 inches long. Urination occurs. The face has assumed a baby’s profile, and muscle movements are more coordinated. At this age, he or she will seize an object placed in the hand.

The baby now sleeps, awakens, and exercises its muscles energetically - turning his head, curling his toes, and opening and closing his mouth. The palm, when stroked, will make a fist. The baby is breathing amniotic fluid to help develop his respiratory system.

Fine hair has begun to grown on the head and sexual differentiation has become apparent.

By the end of this month, the baby is eight to ten inches long and weighs half a pound or more. The mother will probably start to “show” now.

The ears are functioning and there is evidence that the baby hears quite a bit: the mother’s voice and heartbeat as well as external noises.

18 weeks: The child at this age has almost reached viability. Viability is the time when the baby is able to survive outside the mother’s womb.

Not long ago, viability was at 30 weeks; then it was 25 weeks. Now viability is
even earlier. What will it be tomorrow? Science is constantly making progress in this area.

Half the pregnancy has now passed, and the baby is about 12 inches long.

The mother has definitely begun to feel movement by now. If a sound is especially startling, the baby may jump in reaction.

Babies are routinely saved when born prematurely at 21 to 22 weeks after fertilization, and in some cases, even younger – babies have lived when born at 19 weeks!

6th Month:Oil and sweat glands are functioning. The delicate skin of the growing baby is protected from the fetal waters by a special ointment called “vermix”. If the baby were born at this month and given proper care, he would survive.

7th Month: The baby now uses the four senses of vision, hearing, taste, and touch.
She can recognize her mother’s voice.

8th Month: The skin begins to thicken with a layer of fat stored underneath for insulation and nourishment. Antibodies increasingly build up. The baby absorbs a gallon of amniotic fluid per day; the fluid is completely replaced every three hours.

9th Month: Toward the end of this month the baby is ready for birth.The average duration of pregnancy is 280 days from the first day of the mother’s last menstrual period, but that varies. Most babies (85-95%) are born somewhere between 266 and 294 days. By this time the infant normally weighs six to nine pounds, and his heart is pumping 300 gallons of blood per day. He is fully capable of life outside the womb.

Note: All babies develop differently. Thus, the timeline above is a representation of the average baby's development during the first 9 months of life. Images are the work of photographer Lennart Nilsson, and are used in accordance with the Fair Use Doctrine.