It is important to obtain images of both hips because comparison views of the unaffected side can be helpful in identifying true pathology versus an anatomical variant As with all musculoskeletal ultrasound, it is important that the probe be held perpendicular to the skin and as parallel to the femoral neck as possible; a slightly oblique angle may cause the synovial space to appear falsely hypoechoic (an artifact known as anisotropy) Finally, these authors have found that the accepted criteria for the diagnosis of hip effusion may be misleading in some patients A patient with small bilateral effusions (less than mm) may not meet official criteria by measurements, but if the joint space appears convex with anechoic fluid within it, an effusion is likely present FIGURE 131.14 Probe position for hip ultrasound GENITOURINARY ULTRASOUND First Trimester Ultrasound Abdominal pain in the pregnant adolescent female is a common presenting complaint The differential diagnosis is broad, ranging from benign self-limited conditions to a spectrum of life-threatening and organ-threatening conditions Ectopic pregnancy must be identified and treated rapidly It is the leading cause of maternal mortality in the United States and has a reported prevalence as high as 8% for a pregnant patient presenting to the ED