Which ultrasound finding is diagnostic for placenta previa?

• A. Placenta covering the cervical os on ultrasound
• B. Placenta detached from the uterus
• C. Ovarian cyst on ultrasound
• D. No placental signs on ultrasound

Answer: (A)

Placenta previa is diagnosed on ultrasound by identifying placental tissue that covers the internal cervical os, or is located in the lower uterine segment very close to it. This position defines previa, since the placenta lies near or over the opening of the cervix, which can lead to painless vaginal bleeding later in pregnancy and affects delivery planning (often requiring cesarean delivery).

Other ultrasound findings tell a different story: a placenta detaching from the uterus indicates placental abruption, which typically causes painful bleeding and a tender uterus; an unrelated finding like an ovarian cyst has no bearing on placental placement; and no placental signs would suggest the placenta isn’t in a previa position. Transvaginal ultrasound is especially accurate for confirming placental location relative to the internal os.