Patency Criteria based on Historical Evidence

>8-10 seconds of flow through tubal ostium to interstitial part (min criteria), visualization of tubal course*, bubbles around ovary, bubbles in pouch of Douglas.
Volpi, Ultrasound Obstetrics Gynecology. 1996;7:43-48.
* dependent on location and experience of operator.

>5 seconds of flow between pars intramuralis and isthmus tubae without interruption and hydrosalpinx formation and/or fimbrial turbulence to cul-de-sac.
Tüfekei, Ultrasound Obstetrics Gynecology. 1996;7:43-48. 
Allahbadia, Fertility and Sterility. 1992;58(5):901-907.

It is not always possible to scan the entire tube. The uterine-tubal junction often can be visualized with fast or slow flow, but the rest of tube cannot be seen fully because of distortion of the salpinx or an abnormal position of the uterus. Flow in these cases might be visible only in the distal part of the tube near the ovary. It can be inferred indirectly that the tube must be patent.
Heikkinen, Fertility and Sterility. 1995;64(2):293-298.

Possible Occlusion based on Historical Evidence

Almost all patients with bilateral obstruction complained of acute groin pain that subsided on releasing injection pressure on the syringe.
Allahbadia, Fertility and Sterility. 1992;58(5):901-907.

Tubal spasm may give a false-positive result. A second transvaginal sonographic exam or another tubal patency test can rule this out before the patient undergoes laparascopy.
Volpi, Ultrasound Obstetrics Gynecology. 1996;7:43-48.

The exam was interrupted for a short period to allow any possible tubal spasm to ease up.
Heikkinen, Fertility and Sterility. 1995;64(2):293-298.

Occasionally one tube is clearly patent while the other is not. Rotation of the patient from supine to the lateral decubitus position can elevate the non-visualized side.
Jeanty, Journal Ultrasound Medicine. 2000;19:519-527.