By the third trimester both you and your partner are anticipating the birth of your child. You may be becoming impatient with your body and feeling vulnerable and dependent on others. During the last part of the third trimester, many women experience a burst of energy and become engaged in setting up and preparing their home for a child. Both you and your partner may be feeling some anxiety about the coming birth and feel pressured that the time is getting short before the arrival of the baby. You may continue to have vivid dreams about your child especially during your first pregnancy.
Physically, the third trimester is more uncomfortable. You may experience some of the following:

backache
leg cramps
heartburn
a dark line called linea nigra may appear running down from the naval
shortness of breath
the need to urinate frequently
the loss of bladder control when you sneeze or cough
Braxton-Hicks contractions (painless contractions of the uterus)
Also check the following list for signs which should prompt you to call your doctor or midwife.
At 38 weeks, the uterus will have reached the breastbone and you may begin to experience early signs of labour.

During this period, the most dramatic change in the fetus is its continued growth. By the seventh month it weighs about two and a half pounds and is approximately 15 inches in length. By the eighth month the fetus weighs about 5 pounds and is 16 to 18 inches long. During the last month of pregnancy the fetus weighs seven or eight pounds and may be more than 20 inches long. In addition:

skin wrinkles become less pronounced as body fat accumulates and begins to smooth out the body
eyes open and close
fetus responds to light
lanugo disappears
fetus stores iron and builds skeleton
The head (or whatever part will be born first) settles into the pelvic canal between 37 and 40 weeks. This is called engagement or lightening. You will likely notice that the fetus' position has changed and you may feel increased pressure on your bladder.