Pearls and pitfalls in first-trimester obstetric sonography.

Ultrasound is the primary imaging modality used in the evaluation of first-trimester vaginal bleeding and pelvic pain. This article will summarize the ultrasound findings in normal first-trimester pregnancy, failed pregnancy, ectopic pregnancy, subchorionic hemorrhage, retained products of conception, and gestational trophoblastic disease. Mastery of the spectrum of sonographic findings in the normal and abnormal first-trimester pregnancy allows the radiologist to make accurate diagnoses and helps to appropriately guide patient management.