Sonographic diagnosis of an interstitial pregnancy in an asymptomatic patient at 7 weeks' gestation

An interstitial pregnancy is an ectopic pregnancy located within the proximal intramural segment of the Fallopian tube traversing the myometrium. This type of ectopic pregnancy is relatively rare, occurring in approximately 1%-3% of all ectopic pregnancies. Given the myometrial mantle surrounding the gestational sac, which is considerably thicker than in other tubal pregnancies, patients with interstitial pregnancies classically manifest symptoms later in gestation. Thus, there is an increased risk of life-threatening intraperitoneal hemorrhage upon rupture of the myometrium encompassing the pregnancy. We present an unusual case of early sonographic diagnosis of an interstitial pregnancy in an asymptomatic patient at 7 and 3/7 weeks' gestation, discuss predisposing factors, hallmarks of sonographic diagnosis, and review the literature regarding available clinical management modalities. With the increasing application of point of care ultrasound (POCUS) by emergency room physicians and other providers in outpatient facilities, our case emphasizes both the importance of correct sonographic identification of interstitial pregnancy and the clinical importance of uniform early first-trimester sonography, preferably no later than 7-8 weeks' gestation.