Which condition is associated with sudden, painless vaginal bleeding during late pregnancy?

The condition associated with sudden, painless vaginal bleeding during late pregnancy is placenta previa. This condition occurs when the placenta partially or completely covers the cervix, which can lead to painless bleeding as the pregnancy progresses. As the uterus expands and the cervix begins to change in preparation for delivery, the placental tissue can become disrupted, resulting in bleeding. The absence of pain distinguishes this type of bleeding from other conditions such as placental abruption, which is typically associated with painful bleeding.

In contrast to placenta previa, placental abruption involves the premature separation of the placenta from the uterine wall and often presents with painful bleeding and abdominal pain. Vasa previa, while also concerning because it involves fetal vessels being located near the cervix, is less common and can lead to fetal complications if not managed appropriately but does not typically present with sudden, painless vaginal bleeding. Uterine rupture is a rare and severe complication of pregnancy, often associated with intense abdominal pain and potentially fetal distress, rather than painless bleeding. Therefore, the defining characteristic of painless bleeding during late pregnancy clearly aligns with placenta previa.