Learn about Embryonic - Fetal Development

After the first stage of fertilization and cell division, the next stage in human development is the growth of the embryo. At three weeks, the embryo has a primitive heart and a neural tube which will develop into the eyes, brain and nervous system. At this point, it is about 600th-800th of an inch long. At five weeks the eyes develop and the beginning of arms and legs appear.

For the next few weeks, growth is rapid with eyes, ears, fingers and toes becoming identifiable. At eight weeks, the embryo is 1/10-2/10 inches long. By now all of the organ systems are developed and at this point the embryo is known as the fetus.

At four months, the fetus is grown considerably to 5/10- 3/10 inches in length and about six ounces in weight. Most of its external features are formed with hair, eyebrows and eyelashes growing as it approaches its fifth month. From this point on, the fetus will grow in size and weight until birth at about seven pounds.


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