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Prenatal Heath Care

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...