Final answer:
Pregnant women often suffer from back strain late in their pregnancy due to the expansion of the uterus.
Step-by-step explanation:
One of the reasons why pregnant women often suffer from back strain late in their pregnancy is due to the expansion of the uterus. During the third trimester, the uterus expands rapidly and makes up a larger portion of the woman's abdomen, placing pressure on the back muscles. This increased weight and pressure can lead to back pain and strain.