The fetus (Third Trimester)
- Category: The female reproductive system
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In the third trimester of pregnancy, the fetus becomes capable of life outside the womb. Fat begins to accumulate, filling out a scrawny body and preparing the baby for warmth in the outside world. The normal fetus gains three to four pounds during the eighth and ninth months.
At the time of birth, a normal fetus is so big that it has almost outgrown its food supply, since the placenta has stopped growing and cannot keep up with the growing need for nourishment. In the last three months, the brain develops very rapidly. In the last two months, a fatty substance called myelin develops. This speeds up the transmission of nervous impulses and forms a sheath around the nerve fibers.
All this time, the baby is gaining more weight. It sheds the down which covers most of the body and the hair on its head may grow very long - long enough, in fact, that the mother may tie a ribbon in a baby's hair right after birth.