Saline Infusion Sonography (SIS) is a type of transvaginal ultrasound scan in which your doctor will insert a speculum to be able to pass a small catheter into the womb. Then small amount of saline fluid (salty water) is passed into the cavity of the womb to give us a better assessment of the cavity. The procedure it not painful. You may experience some mild cramps during the passage of fluid. The cavity of the womb is assessed for the shape and presence of any abnormality such as polyp or fibroids. This should not take more than 10 minutes.