Objectives:

List the three stages of prenatal development. Discus the two principles of prenatal development. State the characterized of each prenatal

development stage. Explain why defects and miscarriages most often

occur during embryonic stage. Describe several developmental changes that

occur during each month of pregnancy. Discus environmental influences can affects

prenatal development. Identify techniques can assess a fetus’s health.

Gestation)) Stages of prenatal development

1. Germinal 2. Embryonic 3. Fetal

During these three stages of gestation the original single celled zygote grows into an embryo and then a fetus.

Growth and motor development occur from top to bottom and from the center of the body outward.

Development proceeds from the head to the lower part of the trunk.

Developmental Principles

1. Cephalocaudal Principle Development proceeds from the head to

the lower part of the trunk. An embryo’s head, brain, eyes develop

earliest and are disproportionately large until the other parts catch up.

At 2 months of gestation, the embryo’s head is half the length of the body.

By the time of birth, the head is only one fourth the length of the body.

2. Proximodistal principle:

Development proceeds from parts near the center of the body to outer ones.

The embryo’s head and trunk develop

before the limbs, and the arms and legs

before the fingers and toes.

1 .Germinal Stage From fertilization to 2 weeks of

gestational age. Within 36 hours after fertilization, the

zygote enters a period of rapid cell division and duplication (mitosis).

3-4 days zygote down to the uterus, form a blastocyst which floats freely in the uterus for a day or two and then begins to implant itself in the uterine wall.

Germinal Stage cont.

10-20 % of blastocyst become embryos mass, this mass will differentiate into three layers.

Ectoderm will become (layer of skin, nails, hair, teeth, sensory organs, and nervous system).

Endoderm will become (digestive system, liver, pancreas, salivary glands and respiratory system).

Mesoderm will develop and form inner layer of skin, muscles, skeleton and excretory and circulatory systems.

Germinal Stage cont.

Other parts of blastocyst begin to develop into organs that will nurture and protect embryo.

Amniotic cavity or amniotic sac. Placenta Umbilical cord

Nutrients from the mother pass from her blood to the embryo blood vessels, via umbilical cord.

Embryonic blood vessels in the umbilical cord carry embryonic wastes to the placenta, where they can be eliminated by maternal blood vessels.

Embryonic Stage (2 to 8 weeks)

Characterized by rapid growth and development of major body systems and organs.

This is a critical period when the embryo is most vulnerable to destructive influences in the prenatal environment.

Fetal Stage (8 weeks to birth)

During this period, The fetus grows rapidly to about 20

times its previous length, and organs and body systems become more complex.

First month Growth is more rapid The embryo size 10.000 times greater than

the zygote. Length ½ inch. Small heart beats (65 times a minute). Very small veins and arteries. The sex cannot be detected.

Second Month The fetus is less than 1 inch in long. Weighs only 9 gm. The head is half its total body length. Facial part are clearly developed. The arms have (hands, fingers) and the legs

have (knees, ankles and toes). The fetus has a thin covering of skin. Bain impulses coordinate the function of the organ system. Sex organs are developing. The heart beat is steady.

Third Month Length 3 inches. Weight 28 gm. The head one third its total length. Sex can easily be detected. The organs systems are functioning. (breath, swallow amniotic fluid into the lung and expel it , urinate). Movement and reflexes activities.

Fourth Month

The head one fourth of the total body length. Measures 8-10 inches. Weight about 170 gm. The umbilical cord is as long as the fetus

and will continue to grow with it. The placenta is fully developed. Quickening. Reflexes activity become brisker due to

increase muscular development.

5 Month Weighing about 1 pound (454 gm). Measuring about 12 inches. Signs of individual personality appears.

Sleep –Wake patterns. Position in the uterus (lie). Stretching, squirming.

The sweat and sebaceous glands are functioning.

Eyebrows, eyelashes, fine hair on the head, and lanugo hair.

6 Month 14 inches long. Weights 1 ¼ pounds. Has fat pads under the skin. The eye are complete, closing, opening,

and looking in all directions. It can her.

Seventh Month

About 16 inches long and weighing 3 to 5 pounds.

Fully developed reflex patterns. Cries, breathes, and swallows and it may be

suck its thumb. The lanugo may disappear. Continue grow head hair.

8 Month

18-20 inches long. Weight 5-7 pounds. A layer of fat is developing over

the foetus's entire body. Movement are curtailed or imperfect.

9 Month About week before birth the fetus stop

growing. Reached an average weight of about 7 ½

pounds and length of about 20 inches, with boys little longer and heavier than girls.

The organ systems are operating more efficiently.

The heart rate increases. More wastes are expelled through

the umbilical cord.

New born

Environmental influences (Maternal Factors)

1. Nutrition and maternal weight.2. Physical activity and strenuous work.

Regular exercise prevents constipation and improve respiration, circulation, muscles tone, and comfortable pregnancy, safer delivery.

Strenuous working may be associated with premature birth.

3. Drug Intake

Nearly thirty drugs have been found to be teratogenic in clinically recommended doses.

( antibiotic, several hormones, certain anticancer, and aspirin and other non steroidal anti- inflammatory drugs.

No medication be prescribed for a pregnant or breast feeding woman unless it is essential for her health or her child’s.

4. Alcohol drinking even small amount may harm a fetus.

Moderate to heavy drinking during pregnancy disturb an infant’s neurological and behavioural functioning.

5. Smoking Women who smoke during pregnancy have low

birth weight babies.6. HIV / AIDS

The virus transmitted through the placenta to the fetus’s bloodstream.

After birth the virus can be transmitted through breast milk.

7. Other Maternal Illnesses

Rubella leads to deafness and heart defects in baby.

Diabetes Toxoplasmosis infection.

8. Maternal stress. 9. Maternal age.

10. Outside environmental hazards. Air pollution. Chemicals. Radiation. Extremes of heat and humidity.

Monitoring Prenatal Development

What techniques can assess a fetus’s health and why is prenatal care important?

Ultrasound (sonogram).FetoscopyAmniocentesis Chorionic villus sampling.Umbilical cord samplingMaternal blood test