The stages of human fetal development are systematic and indeed quite marvelous. It is fascinating to learn how an embryo develops into a full grown baby. Using ultrasound and other testing procedures, it is possible for us today to observe the growth of the baby at every stage of fetal development. Here’s a month by month summary on the stages in fetal development.
In the first month, major fetal development occurs. During this time, the union between the sperm and egg has taken place and the result is a zygote, which is a single cell consisting of a pair of chromosomes.
A week after fertilization has taken place; the zygote begins to form into a cluster of cells as cell division takes place quite rapidly. About twelve days after fertilization, the cells form into an embryo. At the end of this month, the embryo grows to about a quarter of an inch in length and its major organs such as the heart, liver, lungs and kidneys have begun to develop. In the second month, the embryo’s facial features start forming. Its arms and legs also start developing and become stronger. Its heart is now fully functioning and in the eight week, it is referred to as a fetus. In the third month, the fetus finally begins to appear like a baby. It grows to almost double its length and its fingers, earlobes and eyelids begin to take shape. It also starts sucking its thumb, nodding its head and curling its little fingers into a fist. Its reproductive organs are still in the developing stages during this time. In the fourth month, the fetus’ bones start growing stronger and its reflexes also develop. It is also able to hear outside sounds such as the mother’s heart beat. It weighs about 6 ounces and grows to about 6 to 7 inches in length.
In the fifth month, the fetus grows hair, and the mother may even be able to feel its movements. Eyelashes and eyebrows grow and the body is covered by fine hair called lanugo. It weighs about one pound now. In the sixth month, the second trimester is over and during this time, fetal lung development stages is fully completed, and its facial features become more distinct. It starts to blink, kick and shift and its muscles begin to develop. It weighs about two pounds now. In the seventh month, the fetus’ taste buds develop and layers of fat tissue start forming on the body. Its organs continue to develop and its weight lies between 2 ½ to 3 pounds. The eight month sees very quick growth. The organs are mostly developed during this time and the stages of fetal brain development are almost complete. Its fingernails have also grown by this time and it weighs about four to six pounds. In the last ninth month, the baby is fully developed. Its lungs will however continue to mature till birth. The baby weighs about seven pounds and is now ready to enter the outside world.