Final answer:
During the third trimester of pregnancy, a patient might experience hypotension while lying supine due to the compression of the inferior vena cava by the gravid uterus.
Step-by-step explanation:
A patient in the third trimester of pregnancy might experience hypotension while lying in a supine position in the dental chair. This condition is known as supine hypotensive syndrome or vena cava syndrome, which occurs because the gravid uterus can compress the inferior vena cava, reducing the return of blood to the heart and leading to lowered blood pressure. To mitigate this condition, a simple adjustment involves having the pregnant patient lie on her side rather than flat on her back, relieving the pressure on the vena cava and restoring normal blood flow dynamics. This precautionary measure ensures the well-being of both the mother and the developing fetus during dental procedures in the latter stages of pregnancy.
External symptoms of this may include dizziness or light-headedness, and it can be alleviated by having the patient lie on her side rather than flat on her back.