How is placenta previa most commonly diagnosed?

Placenta previa is most commonly diagnosed through transvaginal ultrasound because this imaging technique provides a clearer and more detailed view of the lower uterine segment and the location of the placenta in relation to the cervix. Transvaginal ultrasound is particularly effective for visualizing the placenta in cases where it is low-lying or covering the cervix, which is not as easily assessed with transabdominal ultrasound.

Transabdominal ultrasound can also be used in the diagnosis of placenta previa; however, it may not provide the same level of detail in evaluating the placenta's position. CT scans are generally avoided in pregnancy due to radiation exposure risks to the fetus, and pelvic exams, while useful in some contexts, do not provide the necessary imaging to accurately determine the placenta’s location. Therefore, transvaginal ultrasound is the preferred method for diagnosing placenta previa due to its accuracy and safety.