As an attempt to document the impact of uterine contractions on potential embryo expulsion, an exploratory evaluation of the movement of an ultrasound contrast agent (SONOVUE)administered intrauterinely via an embryo transfer catheter during the mock embryo transfer was performed. The anatomical point of release of the ultrasound contrast agent (correct or incorrect deposition site, and estimated distance from fundus) as well as any immediate movement (yes/no) of the bolus was recorded by the central independent assessor.