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PRENATAL DEVELOPMENT. Prenatal Development. Life begins in the reproductive system of the female, set inside the pelvic cavity. The term “natal” means “birth”… so pre-natal means before birth. Fallopian Tube. Endometrium (uterine wall). Ovum is ripening inside follicle. Ampulla. Fimbria.

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Prenatal Development

Life begins in the reproductive system of the female, set inside the pelvic cavity.

The term “natal” means “birth”… so pre-natal means before birth.


Fallopian Tube

Endometrium (uterine wall)

Ovum is ripening inside follicle




Maturing follicles


Cervix… a mucous plug forms in this area during pregnancy

Uterus (womb)



Egg maturation and ovulation is stimulated by two hormones secreted by the pituitary gland- follicle stimulating hormone (FSH) and luteinizing hormone (LH). Approximately every 28 days, at the start of a cycle, these hormones cause several follicles to start growing. Of these, only one matures to form a large fluid-filled structure that contains a ripening egg. When the egg matures it is released from the follicle when the follicle ruptures…in a process called ovulation. This occurs on about the 14th day of the cycle.

The egg contains 23 chromosomes…the mother’s genetic material.


The egg, or ovum, slowly travels through the fallopian tube, and if sperm are present at that location, one may unite with the ovum in a process called fertilization. Only one sperm can enter the egg’s outer membrane. The moment the sperm penetrates the egg is called conception, creating a new and separate cell called the Zygote.

The penetrating sperm loses it’s tail, the head dissolves, and out spills it’s genetic material…23 chromosomes.



The fertilized egg now has 23 PAIR, or 46 chromosomes. Immediately the cell begins to duplicate, taking approximately 30 hours to complete the first cell division.

At an increasingly faster rate, new cells are added until they form a hollow, fluid-filled ball, called a blastocyst (about 4 or five days after conception).

Approximately 60 to 70 cells form the blastocyst. Those on the inside (called the embryonic disk) will become the new organism whereas those on the outside will provide the protective covering.


Multiple births can occur two different ways. Sometimes two (or more) different eggs are released, and both are fertilized by two different sperm. The result is fraternal twins. They may be both boys or both girls or one of each; they may or may not look similar. In other cases, a single egg fertilized by a single sperm will split completely in half during that very first cell division. This results in identical twins. They will both be of the same sex and will look very similar if not the same. Identical twins have identical DNA, but different fingerprints!


All the time an egg has been ripening and preparing for ovulation, the endometrium of the uterus has been forming a nutrient-rich lining. It is preparing to receive a fertilized egg. (If no egg is fertilized, this lining will leave the body during a process called menstruation.)

Around the seventh or ninth day after conception, the blaystocyst burrows into the uterine lining in a process called implantation. The protective covering quickly develops into the amnion, surrounding the organism in amniotic fluid. A yolk sac also develops, producing blood cells until the liver, spleen, and bone marrow is mature. The woman’s ovaries produce massive doses of the hormoneprogesterone, signaling the body that a pregnancy is in progress.


Nerve growth begins when a sheet of cells on the back of the embryo folds in the middle to form a tube, which will become the future spinal cord. At one end tube enlarges to form the brain\'s major sections. The amniotic fluid that cushions the fetus begins to form.

Week 4


5 weeks -  At this time the embryo is still the size of a raisin. Low on the sides of the head are two folds of tissue that will become the ears. Although not completely developed, all the major body organs and systems are formed. The neural tube enlarges into three parts, that will soon to develop to become a very complex brain. Also the placenta begins functioning, including the chorionic villi and the umbilical cord, through which the baby will receive nourishment and oxygen. The spine and spinal cord grows faster than the rest of the body at this stage and will give the appearance of a tail. This disappears as the baby grows.

WEEKS 5 & 6

The “tail” in this “tadpole” stage is found in many organisms, so was used as evidence in Darwin’s theory of evolution.

6 weeks - The embryo\'s tiny heart begins to beat. The embryo itself is about a 1/4 inch long. Other major organs, including the kidneys and liver, have begun to develop, and the neural tube, which connects the brain and spinal cord, closes. The physical sensations of pregnancy start--nausea, fatigue, sore breasts and frequent urination.


There are two patterns of development occurring throughout development of the being…

  • Cephalo-caudal, meaning head to tail, top to bottom
  • Proximal-distal, meaning inward to outward

(the head before the heart; the internal organs before the limbs)



7 weeks - The embryo\'s hands and feet are shaped like paddles, but the fingers are beginning to take shape. The embryonic tail has almost disappeared. The pituitary gland is also forming and the fetus is beginning to grow muscle fibers. The heart has divided into the right and left chambers and is beating about 150 beats a minute which is about twice the rate of an adult. The baby\'s facial features are visible, including a mouth and tongue. The eyes have a retina and lens. The major muscle system is developed, and the baby starts to practice moving. The baby has its own blood type and the blood cells are produced by the liver now instead of the yolk sac.


8 weeks-The unborn baby is now called a fetus. The fetus is protected by the amniotic sac and filled with fluid. Inside the child swims and moves gracefully. The fetus is now about 3/4 inches long. The arms and legs have lengthened. During this time of development, the baby\'s head appears much larger than the body because the brain is growing very rapidly. Brain waves can now be measured. The teeth and the palate are beginning to form and the larynx is developing. Through its parchment-thin skin, the baby\'s veins are clearly visible. By the eighth week the ears begin to take shape.

9 weeks - Though the fetus is constantly moving, you won\'t be able to actually feel fetal movement for several more weeks. All of the organs, muscles, and nerves are in place and beginning to function. As the hands and feet develop fingers and toes, they lose their paddle-like look, and the touch pads on the fingers form.

WEEKS 8 & 9



WEEKS 10-11

10 weeks - The fetus weighs about 1/3 of an ounce. The heart is almost completely developed and very much resembles that of a newborn baby. The eyelids have fused shut. The wrists and ankles have formed and the fingers and toes are clearly visible. Genitals have begun to form, but it is too early to tell the sex of the fetus.  

11 weeks - The vital organs--the liver, kidneys, intestines, brain and lungs--are fully formed and may begin to function, while the the head is almost half the length of the entire body. The fetus is only about 2 inches long and weighs less than a half ounce but it is busy moving and kicking. 


Vocal chords are complete, and the baby can and does sometimes cry silently. The brain is fully formed, and the baby can also feel pain. The fetus may even  suck his thumb. The eyelids now cover the eyes, and will remain shut until the seventh month to protect the delicate optical nerve fibers. The hair is on the head and the fingers and toes have developed soft nails. The kidneys are developed and begin to secrete urine.

The skull is not solid bone, but has formed in sections. These sections can overlap during the birth process. There are even a couple of soft spots where bone has not formed at all called fontenals.


During this first trimester period of “formation”, many things can go wrong. Sometimes the woman’s body will self-abort. This is called a miscarriage.



Umbilical cord




Amniotic sac filled with amniotic fluid

Mucous Plug

Caution!... besides oxygen and nutrients, the cord delivers nicotine, alcohol, drug compounds, and other things ingested, inhaled, or absorbed through the skin of the mother.



Nutrition is extremely important during pregnancy. Eating a well-balanced diet can prevent birth defects in the fetus, low-birth weight/mortality of the infant, a difficult labor/delivery, and mortality of the mother during childbirth. The fetus is creating new bones, blood cells, tissue, etc. If it does not receive the nutrients it needs through mother’s diet…it will get it by taking it out of mother’s own system, i.e. robbing calcium from the mother’s bones to build it’s own bones. If deficiencies exist, problems may show up right away or years later.

Common health problems developing during pregnancy

Preeclampsia and Eclampsia (high blood pressure)Gestational DiabetesInfections (toxemia)Clotting Disorders

Common disorders of pregnancy

Placental ProblemsPreterm LaborPreterm Premature Rupture of the MembranesFetal complications

Congenital AbnormalitiesGrowth Abnormalities

Remember exercise and the emotional health of the mother as well!



Weeks 13-16

By now, the fetus has grown large enough that the movements can sometimes be felt by the mother. Often felt like a flutter or a "flip-flop", these first movements that can be felt by the mother is called quickening.


At the end of the fourth month, white, downy hair called lanugo (lu- noo- go) covers the entire body of the fetus. It provides warmth, since the fetus has no layer of fat beneath the skin yet.

At some point later, a white waxy, cheese-like substance also forms over the entire surface of the skin. This is called vernix caseosa. The vernix is a perfect skin lotion, which along with the lanugo, protects he skin from the constant exposure to amniotic fluid. It is also believed that it serves as a sort of skin cleanser and antibacterial substance. The lanugo and vernix caseosa diminishes in amount during the last weeks of the gestation period and usually rubs off during delivery. The presence of a great deal of vernix or lanugo at the time of birth, therefore, is often a sign of prematurity.


The fetus also shows a sensitivity to light and can be stimulated and irritated. However, it still has a long way to go before it is mature enough to survive outside of the womb.

Although there are a few cases of infants being born and surviving at this time, the chance of survival (and without later complications), is very slim.

During the 5th month, at 22 weeks, the fetus weighs a little over 1 pound, and is about 1 foot in length. At this time, the movements can clearly be felt by the mother and by others who place their hands over the mother\'s abdomen.



During the 4th-6th months, most of the organs that were formed during the first trimester begin to function. If born at this time, the fetus has a chance survival. The point in which it can first survive is referred to as the age of being viable and occurs sometime between 22 and 26 weeks.





At only about 3 pounds, the 7 month old fetus has a few pounds to go before reaching the average 7.5 pounds.

During this time, the brain continues to develop at an increasingly fast rate. By 7 months, the fetus clearly responds to sounds outside of the womb, and develops a preference for the tone and rhythm of its mother\'s voice.


7 & 8

By the eight month, the fetus has little room for large movements. During this month, a layer of fat is added that will assist with temperature regulation.

The lungs however, still remain immature. If born at this time, the infant will likely require some help with breathing. It is not until the ninth month that the lungs are mature enough to regulate breathing without assistance.


During this last month of the gestation period, baby continues to grow… at a rate of ½ to 1 pound per week. Baby will turn around in the womb, to a head-down position. The lungs are maturing, preparing for that first breath.



Preparing individuals for life and work
  • Strengthening families
  • Empowering communities

Created by Barbara L. Swarthout, Family & Consumer Sciences teacher at Elkhorn High School