Ultrasound of the postpartum uterus. Prediction of retained placental tissue.

We reviewed ultrasound images an 53 postpartum patients referred for possible retained products of conception and correlated specific ultrasound patterns with clinical and pathologic follow-up. The most common finding in patients with retained placental tissue was an echogenic mass in the uterine cavity, seen in 9 of 11 patients with pathologically proven retained placental tissue. In the remaining 2 patients with pathologically confirmed retained placenta, a heterogeneous mass was seen in the uterine cavity at some point during the course of serial sonography. Retained placental tissue was unlikely when ultrasound demonstrated a normal uterine stripe (n = 18), endometrial fluid (n = 6), or hyperechoic foci in the uterine cavity without an associated mass (n = 17). The latter finding was often associated with recent uterine instrumentation. The sonographic appearance of retained placental tissue is variable, but detection of an echogenic mass in the uterus strongly supports the diagnosis. A heterogeneous mass is sometimes caused by retained placenta, but can also be secondary to blood clots or infected or necrotic material in the absence of placental tissue. Sonographic evaluation for retained products of conception is best done before uterine instrumentation to avoid confusion with iatrogenically introduced air.