Which action can trigger an uncontrolled hemorrhage in a woman with placenta previa?

In cases of placenta previa, where the placenta is positioned over or near the cervix, certain actions can lead to complications, including uncontrolled hemorrhage. Performing a vaginal exam is particularly risky for these patients because it can disturb the delicate tissue surrounding the placenta.

When a vaginal exam is conducted, the cervical manipulation or pressure can cause the placenta to separate from the uterine wall, leading to bleeding. This becomes especially dangerous if the blood vessels embedded in the placenta are ruptured during the examination. Therefore, it's crucial to avoid vaginal exams in patients with known placenta previa unless absolutely necessary and ideally under controlled medical circumstances.

Physical exertion, sexual intercourse, and prolonged standing can also pose risks for a woman with placenta previa by potentially leading to bleeding. However, these actions do not directly interfere with the anatomical and physiological structures surrounding the placenta in the same immediate and impactful way that a vaginal exam does. Thus, the gravity of the risk associated with a vaginal examination makes it the most critical action to avoid in this situation.