Discussion

Angular pregnancies are usually diagnosed via ultrasound. Bollig et al. proposed a set of sonographic criteria for diagnosis, requiring a nonanomalous uterus (excluding unicornuate, bicornuate, or septate variants), implantation of the blastocyst in the lateral angle of the uterine cavity, just medial to the uterotubal junction, and no more than 1 cm of myometrial thickness between the gestational sac and the outer uterine border. The criteria also require completely circumferential endometrium surrounding the gestational sac, confirming an intrauterine gestation, and the absence of an echogenic line bordering the gestational sac in the upper lateral uterus [6]. This set of criteria has not been adopted or enforced by current guidelines. Commonly, these pregnancies are mistaken for cornual, interstitial, or, in our case, intramural pregnancies.

In a recent study, Chen et al. examined whether embryo- and cycle-level factors influence the risk of angular pregnancy following assisted reproductive technology (ART). Their multivariable regression analysis concluded that multiple embryo transfer may increase the incidence of angular pregnancy in ART-conceived pregnancies [7]. Other risk factors for angular pregnancy may include uterine anomalies.

Angular pregnancies that progress to term have been reported to carry an increased risk of intrauterine growth restriction, as well as complications in the third stage of labor, particularly retained placenta. Due to the lack of standardized diagnostic criteria and treatment, management of these complications remains challenging [8]. Most case reports and case series tend to favor expectant management [6,9,10]. In the event of gestational demise, some cases have described the hysteroscopic management of an angular pregnancy, illustrating that hysteroscopy can serve as both a diagnostic and therapeutic modality, allowing direct visualization and minimally invasive, intact removal of the gestational sac [4,11].

These pregnancies are diagnosed at a mean gestational age of 7.4 weeks [6]. Boling et al. followed up two weeks after diagnosis and found that 55% of previously diagnosed angular pregnancies normalized and 14% resulted in early pregnancy loss. Their follow-up management after the two-week follow-up was not detailed in their report. They did state that, of the 13 angular pregnancies that persisted, 11 migrated to a more central location [6].

Though most of these pregnancies result in a live delivery, these pregnancies can lead to uterine rupture, a rare and life-threatening pregnancy complication. In our literature review, we found wide variations of 0%, 12.6%, 13.6%, and 28% of angular pregnancies resulting in uterine rupture [3,5,6,10]. The largest study included 200 cases of angular pregnancies, but the study was done retrospectively, leading to possible selection bias [5].

Risk factors that predispose angular pregnancy patients to uterine rupture are a previous ipsilateral salpingectomy, vaginal bleeding, and gestational age of greater than seven weeks [5]. Low hemoglobin and blood transfusions were the most strongly correlated with uterine rupture in angular pregnancy patients [5]. Early fetal loss is a common sequela of angular pregnancies, with a statistically significant odds ratio of 4.0 when compared to pregnancies without angular pregnancy [12].

One study proposed a classification system of angular pregnancies of type I and type II. Type I angular pregnancies are located at the mediolateral junction of the uterine cavity and surrounded by two circular decidual bands with a partial myometrial border [5]. Type I angular pregnancies are generally safe and can be continued and monitored. Type II angular pregnancies expand laterally and carry a significantly higher risk of uterine rupture and maternal hemorrhage [5]. This classification system was designed as a tool for clinicians to utilize when considering observational management but has not been widely accepted.