Fetus

Pregnancy

Development of Embryo and Fetus

The Fetus
The word fetus (Latin: offspring) is used to describe the growing organism from the beginning of the third month of its life to the moment of birth. During this time, it develops from a small growth of slightly over an inch weighing only a fraction of an ounce into a baby of about twenty inches in length weighing approximately seven pounds. In the first weeks of this development, the male female sex differentiation becomes apparent in the internal sex organs. A little later, the external sex organs develop their characteristic structure. Sometime around the fifth month, the fetal movements become strong enough to be felt by the expectant mother. This so called quickening was formerly believed to be the moment when life entered the new body.
Throughout its growth, the fetus is well protected from injuries as it floats almost weightlessly inside a fluid filled sac called the amniotic sac. At the end of the sixth month, the fetus measures about six inches in length and weighs about one and a half pounds. At this time, the centers of the brain which control breathing begin to develop. It is not entirely impossible (although very unlikely) that such a fetus could actually survive a premature birth. However, the probability of brain damage because of still ineffective breathing is great. The last months of fetal development bring further refinements, such as the temperature control mechanism in the brain and a protective layer of fat under the skin. In the case of a male fetus, the testicles descend into the scrotum. If this descent should fail to occur, corrective measures have to be taken sometime after birth. Otherwise, sterility will result.
During the final weeks before birth, the fetus not only grows rapidly in size, but also gains much of its weight. The birth of a fetus weighing less than five pounds is premature.

[Course 2] [Description] [How to use it] [Introduction] [Conception] [Pregnancy] [Beginning] [Development] [During Pregnancy] [Birth] [Infertility] [Contraception] [Abortion] [Additional Reading] [Examination]