Saline Infusion Sonohysterogram (SIS) / "Bubble Test"

By RRM Academy Reviewed by Dr. Naomi Whittaker, MD, Board-Certified OBGYN, MIGS, NFPMC, FCI Updated May 14, 2026

A Saline Infusion Sonohysterogram (SIS) is a transvaginal ultrasound procedure in which sterile saline is infused into the uterine cavity to enhance visualization of the endometrium and detect structural abnormalities inside the uterus. By distending the cavity with fluid, the clinician gains a clear acoustic window that a standard pelvic ultrasound cannot provide. SIS detects endometrial polyps, submucosal fibroids, intrauterine adhesions, uterine septa, and can reveal an isthmocele (cesarean scar defect), including measurable defect dimensions and residual myometrial thickness.¹²³

SIS occupies a practical middle ground between basic imaging and operative intervention. It is substantially less invasive than diagnostic hysteroscopy and does not require anesthesia. For that reason, it is often considered before proceeding to hysteroscopy when the clinical picture warrants uterine cavity assessment. It also adds information a standard hysterosalpingogram (HSG) may not provide: HSG outlines the cavity contour with contrast; SIS evaluates wall texture, endometrial thickness, and focal lesion detail with ultrasound.

Structural findings from SIS directly inform the fertility workup. Submucosal fibroids, endometrial polyps, and uterine septa are all associated with implantation failure and early pregnancy loss. Asherman syndrome (intrauterine adhesions) may be suspected on SIS and confirmed hysteroscopically. Because these are correctable conditions, identifying them matters. A uterine cavity that appears normal on a standard ultrasound can harbor pathology that SIS resolves clearly.

This content is for educational purposes only and does not constitute medical advice. Consult an RRM clinician or healthcare provider for guidance specific to your situation.