Prenatal Heath Care
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The Embryo
The embryonic stage begins on the 15th day after conception and continues until about the 8th week, or until the embryo is 1.2 inches in length. During this period the cells of the embryo are not only multiplying, but they are taking on specific functions. This process is called tissue differentiation. It is during this critical period of differentiation (most of the first trimester or three-month period) that the growing fetus is most susceptible to damage from external sources (teratogens) including viral infections such as rubella, x-rays and other radiation, and poor nutrition.
A child who has one developmental problem may have other problems that arose at the same time: Kidney problems and hearing problems, for example, are often found together because both kidneys and the inner ears develop at the same time.
In Week 3 we see the formation of the heart, the beginning development of the brain and spinal cord, and the beginning of the gastrointestinal tract.
Teratogens introduced during this period may cause severe problems such as the absence of one or more limbs or a heart that is outside of the chest cavity at birth.
Weeks 4 and 5 –1/4 inch long: Here we see the beginnings of the vertebra, the lower jaw, the larynx (voice box), and the rudiments of the ear and eye. The heart, which is still outside body, now beats at a regular rhythm. Although arm and leg “buds” are visible with hand and foot “pads,” the embryo still has a tail and cannot be distinguished from pig, rabbit, elephant, or chick embryo.
Teratogens may cause very serious problems involving the esophagus, vertebrae, eyes. The baby could be born with severe facial clefts or missing hands or feet.
Week 6 — 1/2 inch, 1/1000 of an ounce: In week 6, we see the formation of the nose, jaw, palate, lung buds. The fingers and toes form, but may still be webbed. The tail is receding, and the heart is almost fully developed.
Teratogens at this point may leave the baby with profound heart problems or a cleft lip.
Week 7 — 7/8 inch, 1/30 ounce (less than an aspirin): This week, the eyes move forward on the face, and the eyelids and tongue begin to form. All essential organs have begun to form.
Teratogens may cause heart and lung problems, a cleft palate, and ambiguous genitalia (not quite male or female).
Week 8 –1 inch, 1/15 ounce: The embryo now resembles a human being. The facial features continue to develop and the external ear appears. Also, we see the beginnings of external genitalia. By now, the circulation through the umbilical cord is well developed. The long bones begin to form and the muscles are able to contract.
Teratogens may still cause heart problems and stunting of the fingers and toes.
The Fetus
At this point the embryo is developed enough to call a fetus. All organs and structures found in a full-term newborn are present.
Weeks 9 to 12 — 3 inches, 1 ounce: The head comprises nearly half of the fetus size and the face is well formed. The eyelids close now and will not