Saline Infusion Sonohysterogram (SIS) / "Bubble Test"

A saline infusion sonohysterogram (SIS) is an ultrasound that uses sterile saline, a salt water solution, to show the inside of the uterus. During a transvaginal ultrasound, a thin tube places the fluid in the uterine cavity, the space inside the uterus. The fluid gently opens the space. This view is clearer than a standard pelvic ultrasound can provide. SIS can detect polyps in the lining and fibroids that bulge into the cavity (submucosal fibroids). It can also detect scar tissue (intrauterine adhesions) and a wall that divides the cavity (uterine septum). It can also show an isthmocele, a pouch in a cesarean scar. SIS can measure the size of that pouch and how much muscle still covers it.¹²

SIS sits between basic imaging and surgery. It is much less invasive than diagnostic hysteroscopy, in which a camera enters the uterus. It does not require anesthesia. For this reason, clinicians often perform it first when the uterus needs a closer look. It also adds detail that a hysterosalpingogram (HSG) may miss. HSG uses dye and X-ray to trace the outline of the cavity. SIS uses ultrasound to assess the uterine wall, the thickness of the lining, and the fine detail of any growth.

The findings of SIS shape the rest of the fertility workup. Submucosal fibroids, polyps, and a uterine septum are all associated with failed implantation and early miscarriage. SIS may raise concern for Asherman syndrome, scar tissue inside the uterus. A hysteroscopy then confirms it. A uterus that appears normal on a standard ultrasound can still hide a problem that SIS shows clearly.