Choice A rationale

Intermittent abdominal pain following passage of bloody mucus is more commonly associated with labor or conditions like bloody show but not specifically indicative of placenta previa.

Choice B rationale

Increasing abdominal pain with a non-relaxed uterus could be a sign of conditions such as uterine rupture or contractions, but it is not a typical sign of placenta previa. In placenta previa, the uterus is typically soft and non-tender.

Choice C rationale

Abdominal pain with scant red vaginal bleeding could be indicative of several conditions, including early labor or placental abruption, but it is not a typical sign of placenta previa. Placenta previa is usually characterized by painless bleeding.

Choice D rationale

Painless red vaginal bleeding is a classic sign of placenta previa. This occurs because the placenta, which is implanted low in the uterus, near or over the cervical os, begins to separate as the cervix effaces and dilates, leading to bleeding.

Choice A rationale: Uteroplacental insufficiency causes late decelerations due to reduced oxygenation, not mechanical pressure. It reflects placental dysfunction, not direct cranial compression effects.

Choice B rationale: Spontaneous rupture of membranes increases infection and labor risk but does not directly alter cerebral perfusion or trigger vagal responses linked to head compression.

Choice C rationale: Altered fetal cerebral blood flow results from cranial pressure during contractions, triggering vagal stimulation and early decelerations. This is the physiological response to head compression.

Choice D rationale: Umbilical cord compression causes variable decelerations due to transient blood flow obstruction, unrelated to cranial pressure or cerebral perfusion changes.