by Stephanie Davis

Created on: December 27, 2010   Last Updated: December 31, 2010

Pregnancy is a wonderful aspect of the human condition and for women the changes in their own bodies are obvious. However, they may not fully understand what is going on with the unborn baby inside of them. Pregnancy is divided into three trimesters, each trimester has it's important milestones of fetal development. In the first trimester the unborn child goes from being a small cluster of cells to a solidly formed human being. The second trimester is often the easiest time of pregnancy as hormones in the woman's body have adjusted to her condition.While the most rapid and dramatic stages of fetal development occur during the first trimester, many changes occur in the second as well.

The second trimester consists of the thirteenth through twenty eighth week of pregnancy. At the start the fetus already has functioning organs, nerves and muscles. At thirteen weeks the intestines push up into the abdomen from the umbilical cord. Urine begins to form and discharge itself into the amniotic fluid. Between weeks fourteen threw fifteen the sex of the baby is apparent and the skeleton forms. During week sixteen facial expressions are possible and the fetuses movement becomes more coordinated. These fetal movements may not be yet felt by the mother, but can be detected via ultrasound. At week eighteen the baby begins to hear and may be able to hear the mothers heartbeat. Concluding the first part of the second trimester is week nineteen in which in females the uterus and vagina form.

The latter part of the second trimester begins in week twenty, this also marks the halfway point of the pregnancy. During week twenty a mother will often feel her baby move for the first time, this is known as the quickening.  Swallowing begins to occur during week twenty one and during week twenty two the baby's hair becomes visible. Foot and finger prints begin to form during week twenty three along with the testes descending in males. During this time female reproductive organs and lifetime supply of eggs are in place. After week twenty with intense medical help a baby born at this stage may survive.  At this stage exploring the uterine environment may become the fetuses primary source of entertainment . By weeks twenty six fingernails have formed and the lungs are begging to produce surfactant. Surfactant is the substance that allows the air sacs in the lungs to inflate and keeps them from sticking together when they deflate.The second trimester ends in week twenty seven and the baby's size has tripled since the week twelve. At this stage the fetus should be about nine inches long and weigh almost two pounds.

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