The incidence and importance of the pseudogestational sac revisited

In a pregnancy of unknown location, an intrauterine fluid collection may represent either the early gestational sac of an intrauterine pregnancy, or as reported in previous literature, the pseudogestational sac of an ectopic pregnancy. Various sonographic features have been used to distinguish these 2 entities, but the clinical relevance of the pseudogestational sac remains unclear.

To establish the incidence and relative rate of intrauterine fluid collection among ectopic and intrauterine pregnancies and to determine if the size of the collection differs between ectopic and intrauterine pregnancies STUDY DESIGN: We performed a retrospective cohort study of women with pregnancies of unknown location and pelvic or abdominal pain or bleeding. We calculated the incidences of intrauterine fluid collections among ectopic and intrauterine pregnancies, including both ongoing pregnancies and spontaneous abortions, given that that our focus was location and not viability. We calculated the relative risk of ectopic pregnancy if an intrauterine fluid collection was present, adjusting for age and vaginal bleeding. We compared the incidences of ectopic and intrauterine pregnancies among those with and without intrauterine fluid collections. Among those with collections, we compared the mean sac diameter between ectopic and intrauterine pregnancies in continuous and categorical fashions.

We evaluated 1236 women presenting with a pregnancy of unknown location. The rates of ectopic and intrauterine pregnancies (including spontaneous abortions) were 13.1% and 63.9%, respectively, with the remainder lost to follow-up. On ultrasound, 452 women (36.6%) had an intrauterine fluid collection. Eight of 162 ectopic pregnancies (4.9%) had a collection, compared with 363 of 789 intrauterine pregnancies (46.0%) (P=.01). Of the ectopics with a fluid collection, 5 had an adnexal mass. The presence of intrauterine fluid collection decreased the risk of ectopic pregnancy (adjusted relative risk, 0.09; 95% confidence interval, 0.05-0.19) after adjusting for age and the presence of bleeding. Among those with an intrauterine fluid collection, the rate of ectopic pregnancy was 2.2%, and the rate of intrauterine pregnancy was 97.8%; among those without a collection, the rate of ectopic pregnancy was 26.7%, and the rate of intrauterine pregnancy was 73.3%. The mean sac diameter did not differ between ectopic and intrauterine pregnancies, whether analyzed continuously or categorically.

In the presence of an intrauterine fluid collection, the rate of ectopic pregnancy is very low. The size of the intrauterine fluid collection in a woman with a pregnancy of unknown location cannot be used to distinguish between a gestational sac and a pseudogestational sac. Pseudogestational sacs are uncommon and of little clinical consequence. In assessing pregnancies of unknown location, clinicians should incorporate the entire clinical picture, including other sonographic findings, to avoid incorrect or delayed diagnoses.