Massive subchorionic thrombohematoma (MST) is the presence of a large hematoma or thrombus confined to the subchorionic space. Sonographic findings vary and include placenta descriptions such as heterogeneous, homogeneous, hypoechogenic, or jelly-like mass, which can be differentiated from the normal placenta. Our case report highlights the serial sonographic features observed in a singleton pregnancy from 13 to 29 weeks of gestation. Ultrasound findings of the placenta changed from a 65 ml subchorionic hematoma at 16 weeks to a well-defined placental mass with cystic areas at 20 weeks to an amorphous gelatinous mass at 23 weeks which became primarily replaced by an anechoic lesion with internal septations at 27 weeks. She delivered a live female at 29 weeks. MST usually has a dramatic initial presentation, but these findings may be compatible with a favourable outcome. Serial ultrasound assessment of the placenta is helpful to define the perinatal prognosis and may demonstrate gradual changes and eventual resolution
