Prenatal Development

Every expectant mom wants to know all she can about prenatal development. It makes you feel a little closer to your baby when you know what's going on in his or her littler world and how he or she has developed as you progress through your pregnancy. Here's a rundown of the prenatal development timetable.

The pregnancy begins, of course, with conception, the fertilization of the egg with sperm. Before this develops into an embryo, several different kinds of cells are formed within the egg:

• First, the ectoderm cells will develop into sense organs and the nervous system.
• The mesoderm cells then make the circulatory, skeletal, and muscular systems.
• Finally, the digestive system and some glands are developed from the endoderm cells.

At this time, a layer of cells is also forming in the uterus, which will become the placenta and will give the baby nutrition. During the first month, the heart begins to beat and the first parts of the nervous and digestive systems begin to form. The embryo is about a quarter of an inch long at the end of the first month and has little bumps where his or her arms and legs will later develop.

By the end of the second month, the embryo has grown to about one and a half inches. Bones, muscles, and the face and neck begin to develop at this time. A lot of focus in the second month of prenatal development is on the brain, so if you saw a embryo during this stage it would have a very big forehead compared to the size of the rest of the embryo.

The third month is when things really start to happen. Sexual differentiation occurs, and there are buds for the baby's future teeth. The organs start to show signs of activity and, by the end of the first trimester, independent movement of the body is possible. You may not feel this movement, but it is happening!

There's a lot of prenatal development going on in the second trimester. This is when the arms and legs fully form and the head becomes a smaller part of the fetus in proportion to the rest of the body. Skin appears red because of the blood coursing through the baby's veins, but as the trimester progresses the skin develops glands, hair, and finger and toenails.

By the end of the fifth month, baby weighs about a pound. At the end of the second trimester, the eyes have completely formed and the eyelids open. By this time, you should be feeling the baby move.

By the beginning of the third trimester, your baby could live outside of the womb. The brain is still developing at this point and complications are high if you deliver at this stage, but it is possible for the baby to live.

The fetus grows a lot during the last trimester, largely because it is finally putting on body fat. The bones are still soft during much of the third trimester. The fetus is considered "full term" at 37 weeks, but babies born in week 36 usually survive.

It can be a lot of fun to track your baby's prenatal development, but remember that these markers are merely estimates. Every baby and every pregnancy is different, so if you're not having the exact week by week events that other people have, there's not necessarily a reason to worry. Enjoy this time with your baby and know that it will be over very quickly and you'll have your little one in your arms before you know it!

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