ABSTRACT
Ectopic pregnancy is defined as implantation of the embryo outside the uterine cavity. Fallopian tubes are the most common location of the ectopic pregnancy. The overall incidence of ectopic pregnancy in the general population is 1% to 2% and increases to 2% to 5% with assisted reproductive techniques. The interstitial part of the fallopian tube originates from the tubal ostium and crosses the myometrium of the uterus with a tortuous course eventually arising from the uterine cavity. Interstitial pregnancies are often diagnosed on the first-trimester transvaginal ultrasound (TVUS) when the patient is asymptomatic. In a case series of 27 interstitial pregnancies with a mean gestational age of 56 days, TVUS successfully diagnosed the interstitial pregnancy in 55.6% of cases. Two-dimensional TVUS has a lower sensitivity to differentiate between interstitial and angular pregnancy. Availability of additional planes in three-dimensional TVUS such as coronal views aids in widespread evaluation of gestational sac in relation to the uterine cavity.
