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The sperm joins with the ovum (egg) to form one cell — the zygote.
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, etc.
This first cell, the zygote, divides within about 10 hours and then cell division continues in an orderly fashion every few hours as the small group of cells travels down the Fallopian tube to the uterus, where the uterine lining has been prepared for implantation.
There are over 100 cells already present when this tiny human embryo (blastocyst) reaches the uterus 7-10 days after fertilization. Upon implantation, complex connections between the mother and the embryo develop to form the placenta.
Day 18 – blood vessels and the heart begin to form
Day 20 – foundations of the brain, spinal cord, and nervous system are already established
Day 25– the heart begins to pulsate and will continue until this person dies; the digestive system and parts of the eyes are forming
Day 28 – the backbone and the rest of the skeleton (cartilage now) and muscles are forming; arm and leg buds are present and elongating
At one month old, the embryo is 10,000 times larger than the original microscopic fertilized egg, and is developing rapidly. The heart is pumping increased 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 to the developing human embryo. The word "embryo" is Latin and means "a budding".
Day 35 – the preborn human embryo now has the 3 main parts of the brain, as well as eyes, ears, nasal organs, liver, and gall bladder; arm and leg buds are dividing into their sections (hand, arm etc.). During this week the heart will divide into 4 chambers and the little human embryo may begin to move.
Day 42 (6 weeks) – brainwaves can be detected on the EEG and the EKG can be recorded. The brain is presently controlling 40 sets of muscles as well as all body organs. Fingers, then toes, begin to form.
The embryo is about 1/5 inch long. Mouth, liver, and intestines begin to take shape. The jaw forms, including teeth buds in the gums. The stomach produces digestive juices and the kidneys have begun to function.
Day 56 (8 weeks) – the human embryo is 1.5 inches long and is now referred to as the "fetus", a Latin word meaning "young one", or "offspring".
The face appears quite human. Hands and feet are distinctively human.
At the end of 8 weeks all organs are present; during the remainder of the pregnancy the organs will mature and become fully operational. For example, the cartilage in the skeleton now begins to be replaced by bone cells.
Day 63 (9 weeks) -The preborn human fetus, the "young one", now sleeps, and exercises her muscles by turning her head, curling her toes, and opening and closing her mouth. The eyelids seal during this time to protect the developing light sensitive eyes which will reopen Week 25.
She can respond to touch by making a tight fist when her palm is stroked. She breathes amniotic fluid while developing her muscles and her whole respiratory system; the diaphragm becomes functional this month. As many as one hundred hiccups an hour have been counted in the "young one" during these early months, possibly to strengthen the diaphragm.
Day 84 (12 weeks) -All the organs and systems of her body are developed and functioning. External genitalia fully differentiate into male or female. Body length has doubled since Week 8 to about 3 inches.
The only major activity that will now take place until birth is growth, the increase in her size.
The human fetus is now about 4-5 inches long and weighs almost an ounce. The muscles begin to develop. Fingernails and toenails develop. The child's spontaneous movements can be observed.
By the end of this month, the preborn child is about 6 inches in length and weighs about 7 ounces. Unique fingerprints are evident and will never change. Her ears are functioning, and there is much evidence that she hears her mother’s voice and heartbeat, as well as external noises. The umbilical cord has become an engineering marvel, transporting 25 quarts of fluid per day and completing a round-trip of fluids every 30 seconds. Because the preborn child is now larger, the mother usually begins to feel her baby’s movements during this month.
Half the pregnancy has now passed, and the preborn child is about 6 inches long. The preborn fetus exhibits good muscular strength and coordination, kicks, moves, and turns in the womb, hiccoughs, and develops sleep-wake patterns. If a sound is especially loud or startling, the young one may jump in reaction to it.
The fetus is now about 6-8 inches long. The child blinks, grasps, and moves her mouth. Hair grows on the head and body.
By the end of the fifth month, the "young one" will be about 10 inches tall and weigh about a pound. Babies born at this time (19-20 weeks) are surviving at an increasing rate thanks to improving medical technology.
Oil and sweat glands are functioning. The delicate skin of the young one is protected from the waters in the amniotic sac by a special ointment called "vernix".
Week 22 The fetus now weighs approximately 1/2 a pound and spans about 10 inches from head to toe. Sweat glands develop, and the external skin has turned from transparent to opaque.
By the end of the sixth month, the "young one" weighs about two pounds and may be up to 12 inches long.
The preborn human fetus now weighs 2-3 pounds and uses the four senses of vision, hearing, taste, and touch. Research has documented that she can now recognize her mother’s voice. About 2 more pounds are added by the end of this month.
The skin begins to thicken, with a layer of fat stored underneath for insulation and nourishment.
Fingernails have reached the tips of the fingers. Antibodies increasingly build up.
The "young one" swallows a large amount of amniotic fluid per day; she has been urinating for several months. The "young one" gains about two more pounds this month.
During these final weeks, approximately 14 grams of fat are laid down per day. The "neonate" weighs about 7-8 pounds and may be 14-20 inches long.
Toward the end of this month, the preborn child is ready for birth. The average duration of pregnancy is 280 days, from the first day of the mother’s last menstrual period; but this varies.
By this time, the preborn child’s heart is pumping 300 quarts of blood per day. The "young one" triggers labor and birth occurs. Of the 45 generations of cell divisions that will occur in every person, 41 take place in the uterus (womb). Only four more will occur during the rest of childhood and before adolescence.
Scientists know a distinct human life begins at conception (fertilization).
From conception (fertilization) onward, the preborn child is a living, developing individual with a uniquely human genetic makeup, different from the mother’s and father’s genetic codes.