What is the standard imaging technique for diagnosing placenta previa?

Transvaginal ultrasound is the standard imaging technique for diagnosing placenta previa due to its high sensitivity and specificity in identifying the location of the placenta relative to the cervical os. This method provides clearer and more accurate images of the lower uterine segment and the cervical canal, which is essential when evaluating placenta previa.

In cases where the placenta is located low in the uterus, transvaginal ultrasound can outline the placental position more effectively than other imaging modalities. It allows for closer examination and is less impacted by abdominal overlying structures, making it ideal for this purpose.

While transabdominal ultrasound can also be used to assess placental location, it may not provide the same level of detail as transvaginal ultrasound, especially in early pregnancy or in cases where the placenta is very low. CT scans and X-rays are generally avoided in pregnancy due to radiation exposure and are not utilized for this specific diagnosis. Thus, transvaginal ultrasound remains the gold standard for evaluating placenta previa.