Final answer:
A pelvic exam is contraindicated in a patient with placenta previa due to the risk it poses for disturbing the placenta and causing bleeding. Ultrasounds are the safest imaging modality during pregnancy, and the lowering of blood glucose after a meal is an example of negative feedback in the body.
Step-by-step explanation:
A patient with placenta previa should avoid certain examinations that might disturb the placental location or increase the risk of bleeding. The kind of examination that is contraindicated in a patient with placenta previa is a pelvic exam. This is because a pelvic exam involves physical examination of the internal genital organs, which can disrupt the low-lying placenta and possibly cause bleeding. Other non-invasive tests like ultrasound, blood pressure monitoring, and blood glucose testing are generally considered safe for patients with placenta previa.
In the context of imaging studies during pregnancy, ultrasounds are considered the safest modality. This takes into account the avoidance of radiation exposure to the fetus, which is a concern with other imaging studies like CT scans, PET scans, and X-rays. When testing for pregnancy using a lateral-flow pregnancy test, a blue band appearing on the control line without any band on the test line generally indicates a negative test for pregnancy. Moreover, an example of negative feedback in the human body is the lowering of blood glucose level after a meal, which helps to maintain homeostasis.