The nine months of pregnancy are divided into three equal parts, known as trimesters. During the first trimester (13 to 14 weeks) all the different parts of the fetus' body are formed. During the second and third trimesters, all these parts grow and develop. By the end of the second trimester (26 to 28 weeks) the foetus is sufficiently well-formed to stand a chance of survival outside the womb.
The umbilical Cord and the Placenta
The fertilised egg (or zygote) which is the start of the human baby divides itself over and over again, and by the seventh day after fertilisation implants itself in the lining of the uterus. For the first six to eight weeks it is known as an embryo. During this time the cells develop rapidly, taking on their individual jobs of forming bone, blood, organs, etc., and by the end of the eighth week the embryo begins to resemble a human.
The developing embryo must be fed and protected. This is done by means of the umbilical cord which attaches it to the placenta. Seven days after implantation the outer cells of the embryo have burrowed into the lining of the uterus and started to form into the placenta. Some of the pregnant woman's cells are broken down to form pools of blood which supply oxygen and food for the baby.
The placenta is a red, spongy disc of tissue. As the fetus enlarges so does the placenta; at birth it weighs about 500 g (1 lb) and is about 20 cm (8 in.) across.
The umbilical cord develops from the placenta to link it with the embryo. During pregnancy the cord gets longer; at birth it is about 50 cm (20 in.) long.
The work of the placenta and umbilical cord is vital, and it is important that nothing interferes with their function. These two organs only grow during pregnancy, and immediately after the baby is born they are expelled (the afterbirth). Did you know there are things you can do to encourage more healthy Fetal Growth and Development? Discover more about pregnancy and birth at http://www.babybirthbasics.com.
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