Final answer:
The dropping of the abdomen, known as lightening, occurs in the third trimester of pregnancy. It relieves pressure on the upper abdomen but increases pressure on the pelvic floor and rectum.
Step-by-step explanation:
The question is about the changes that occur in the last trimester of pregnancy, specifically the dropping of the abdomen.
During the third trimester, as the fetus grows larger, it drops or descends into the pelvis, positioning itself for birth. This dropping of the abdomen is also known as lightening. It relieves pressure on the upper abdomen but increases pressure on the pelvic floor and rectum.
Some symptoms that are commonly experienced by pregnant women during this stage include more frequent urination, back pain, swelling of the lower extremities, varicose veins, and heartburn.