['A Valsalva maneuver is used clinically and on imaging in order to determine female pelvic organ prolapse. We have examined the potential confounding effect of levator co-activation at the time of a Valsalva maneuver and the impact of repetition with biofeedback instruction.', "Fifty nulliparous women at 36-38 weeks' gestation received 3D/4D translabial ultrasound investigation in the dorsal resting position after bladder emptying. Valsalva maneuvers were recorded initially and after repeated attempts with visual biofeedback both during the maneuver and after, with the operator demonstrating findings on the ultrasound monitor, in order to abolish levator co-activation. Offline analysis was subsequently undertaken.", 'Significant differences between first and optimal Valsalva maneuver were found for bladder neck position, bladder neck descent, hiatal sagittal diameter and hiatal area on Valsalva. In a minority of women (22/50) we observed a reduction in the sagittal hiatal diameter on first Valsalva maneuver, indicating levator co-activation. A reduction in sagittal diameter was seen in only 11/50 after instruction. Levator co-activation was associated with significantly lower bladder neck descent.'] Is levator co-activation a significant confounder of pelvic organ descent on Valsalva maneuver?