Final answer:
During the third trimester, the fetus typically gains 6 ½ to 8 ½ pounds. This period marks the most rapid growth phase with significant organ development. Mothers usually experience increased discomfort due to this growth.
Step-by-step explanation:
The fetus typically gains significant weight during the third trimester of pregnancy. This is a period characterized by the most rapid growth, where the fetus grows to about 3 to 4 kg (6 ½ -8 ½ pounds) and reaches a length of approximately 50 cm (19-20 inches). Organ development continues up to birth, and in some cases, such as the nervous system and liver, it continues after birth. During this stage, the mother may experience increased discomfort due to the significant changes in her body and the growing fetus.