Context: The interstitial gestation is a rare form of tubal pregnancy which is associated with high morbidity. The diagnosis of an interstitial gestation can be reached through a bidimensional transvaginal ultrasonography (2D-TVUS), however, sometimes when making use of this technique it is not possible to appropriately evaluate the position of the gestational sac in relation to the uterine cavity. The three-dimensional transvaginal ultrasonography (3D-TVUS) allows accessibility to plans that the bidimensional does not, thus it makes it possible to reach a more accurate diagnosis and it also allows for an appropriate therapeutic planning.
Case report: We present a case of interstitial gestation diagnosed in the sixth week in an asymptomatic woman, who had a previous diagnosis of primary infertility. The 2D-TVUS revealed the presence of a gestational sac outside of the uterine cavity; moreover the colored Doppler and the power Doppler indicated a thriving vascular ring. The 3D-TVUS in the surface and transparency mode demonstrated that the gestational sac was located in the interstitial region of the uterine tube, and the niche mode accurately evaluated the relationship between the gestational sac and the uterine cavity. The patient was successfully treated with a local injection of methotrexate guided by a transvaginal ultrasonography. The 3D-TVUS was of great importance to confirm the diagnosis, to allow appropriate therapeutic choices and to decrease the morbidity.