In which condition does the placenta cover the cervical opening?

The correct answer is placenta previa because this condition specifically involves the placenta implanting in the lower uterine segment, leading to partial or complete coverage of the cervical opening. This can cause significant complications during labor, including bleeding, and often necessitates careful monitoring throughout the pregnancy.

Placenta accreta, on the other hand, refers to an abnormal attachment of the placenta to the uterine wall, which may not directly involve placement over the cervix. Placenta percreta is an even more severe form of attachment, where the placenta penetrates through the full thickness of the uterine wall and may attach to surrounding organs, but again, this does not specifically involve coverage of the cervical opening. Placenta abruption refers to the premature separation of the placenta from the uterine wall, which can lead to bleeding but is unrelated to the position of the placenta in relation to the cervix. Therefore, the unique characteristic of placenta previa is what makes it the correct answer in this context.