Fetal Development - What are the Fetal Development Stages?

Learning About Fetal Development

Once a woman becomes pregnant, her natural desire is to learn everything she can about baby development and to know what's going on with the little person growing inside her womb. One of the best ways to do that is to find a good pregnancy calendar online. Most of them have a service you can sign up for that sends you an email daily telling you about your baby's progress and what to expect at that specific point in your pregnancy. This is particularly useful if this is your first pregnancy, regardless your age - from a teen who is pregnant to a woman in her 30s. It is possible to see fetal development pictures, videos, and diagrams, and to learn from them and the accompanying write-ups how things are going.

The Beginning - The Germinal Stage

The stages of fetal development begin with the germinal stage, which starts at conception when the sperm and egg unite in one of the fallopian tubes, and the fertilized egg, called a zygote, moves to the uterus. This little trip can take up to a week and cell division is occurring very quickly. It begins between 24 to 36 hours after conception and once the cell division begins happening, our zygote changes its name to a blastocyst. There are three layers to the blastocyst, the ectoderm that will become the skin and nervous system; the endoderm that will become the digestive and respiratory systems; and the mesoderm that will become the muscle and skeletal systems. When the blastocyst arrives at the uterus, it attaches to the wall of the uterus in a process called implantation.

A Name Change and Into Stage Two

Once implantation takes place there is another name change and the blastocyst becomes an embryo and will be called an embryo until the cell differentiation is almost complete. The placenta and umbilical cord, and support systems for embryonic development, occur during this period. The various systems of the body begin to take shape now and the basic outlines of the nervous system, organs and body are set. By the end of this stage, at about 13 weeks, you will be able to distinguish the fingers, eyes, mouth, and ears of the baby.

When The Embryo Becomes a Fetus

Fetal development in the second trimester sees the embryo having almost completed the cell differentiation and another name change is in order. Now the embryo becomes a fetus and remains named as such until birth. All of the systems, organs and body continue to develop during the second trimester. The neural tube develops into the brain and spinal cord, and neurons form. By the third month of gestation you will be able to tell if the baby is a boy or girl and around the 16th week you may begin to feel fetal movement. Although the baby has been active all along, until the fetus is larger and heavier, it is difficult to feel the movement. The fetus continues to grow, lengthening and gaining weight, but the bulk of the physical growth will happen in the third and last trimester.

Twin Fetal Development is Different

When a woman is pregnant with twins things are different. Twin fetal development varies depending upon whether the twins are fraternal or identical. Fraternal twins are twice as common in the US as identical twins. Fraternal twins occur when the ovary releases two eggs and they are both fertilized by two separate sperms. The babies are twins in that they are conceived at the same time, but they do not share the same identical genetic makeup because they are separate. Identical twins are from a single sperm-egg pair (zygote) that splits a few days after fertilization. Each part has the same genetic makeup, which means there will be two identical babies.

Regardless whether the twins are fraternal or identical, each will have its own amnion, chorion, and placenta. All fraternal twins do and about one-third of identical twins do. This situation changes if the split occurs between four and eight days after conception, when the blastocyst has moved into the uterus. Two-thirds of identical twins fit into this category. They share the chorion but have their own amnion, therefore they share the placenta as well, however, they are kept apart by a membrane that encircles each baby. In rare occasions this membrane does not divide the babies and the identical twins then share amnion, chorion, and the placenta. It is in these situations that co-joined twins can occur where both babies share certain organs or are joined at various spots on their bodies.

Fetal development is a fascinating and wonderful process to learn about. By educating yourself you will have a good understanding of what is happening in and to your body and your baby's body all through your pregnancy.


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