SYNOPSIS:In this retrospective cohort study of 1,236 women, the rate (2.2%) of ectopic pregnancy was rare among women with a fluid collection (or pseudosac) in the uterus. The size of the fluid collection was not predictive of ectopic pregnancy. The presence of an 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.
SOURCE:Lee IT, Rubin ES, Wu J, et al. The incidence and importance of the pseudogestational sac revisited. Am J Obstet Gynecol 2021; Nov 2:S0002-9378(21)01182-0. doi: 10.1016/j.ajog.2021.10.033. [Online ahead of print].
The pseudogestational sac of ectopic pregnancy represents fluid or blood in the endometrial cavity, rather than a true gestational sac.1 Any fluid collection in the uterus (without a yolk sac or embryo) generally is considered a pregnancy of unknown location that could be a sign of ectopic pregnancy or develop into an intrauterine pregnancy. The classic ultrasound characteristics indicative of an early intrauterine gestational sac, such as the double decidual sign and the intradecidual sign, may not be present when the sac is very small, or may not be present at all.2 The authors of this study wanted to estimate the prevalence of pseudogestational sacs with modern ultrasound techniques and determine whether they were clinically relevant for the diagnosis of ectopic pregnancy.
This is a retrospective cohort study of all women presenting to the Hospital of the University of Pennsylvania between 2013 and 2017 with abdominal or pelvic pain
and/or vaginal bleeding and diagnosed with a pregnancy of unknown location. The subjects were followed in a clinical database until a definitive diagnosis of ectopic pregnancy, spontaneous abortion (SAB), or viable intrauterine pregnancy (IUP) was reached. Data collected included demographics, ultrasound findings, beta-human chorionic gonadotropin (β-hCG) levels, and pregnancy outcomes. The charts were reviewed to determine the presence or absence of an intrauterine fluid collection and groups were compared. An intrauterine fluid collection was defined as a hypoechoic area noted within the endometrium measuring at least 1 mm.
There was a total of 1,236 women included, comprising 13.1% with ectopic pregnancy, 32.4% with IUPs, and 31.5% with SABs. SABs were grouped with IUPs for the analysis, since location of the pregnancy, not viability, was the outcome of interest for this study. The initial ultrasound demonstrated that 452 of the 1,236 participants (36.6%) had an intrauterine fluid collection. Only eight of 162 ectopic pregnancies (4.9%) had a fluid collection compared with 363 of 789 IUPs (46.0%) (P < 0.01). Five of the eight ectopic pregnancies with intrauterine fluid collections also had a suspicious adnexal mass on ultrasound. After excluding those lost to follow-up, of those with an intrauterine fluid collection, 2.2% had an ectopic pregnancy and 97.8% had an IUP. The median mean sac diameter was 4.5 mm (range, 2.5 mm to 13 mm) among ectopic pregnancies and 4.4 mm (range, 1.0 mm to 31.4 mm) among IUPs and did not differ between the groups (P = 0.81). After adjusting for age and the presence of vaginal bleeding, the presence of an intrauterine fluid collection significantly decreased the relative risk of ectopic pregnancy (adjusted relative risk, 0.09; 95% confidence interval, 0.05-0.19).
COMMENTARY
This study provides important information for clinicians evaluating pregnancies of unknown location. A sac-like structure in the uterus with a positive pregnancy test could represent an early gestational sac or a pseudogestational sac of ectopic pregnancy. Ectopic pregnancy potentially is life-threatening; therefore, making a timely diagnosis is critical. Typically, evaluation of pregnancies of unknown location includes a combination of clinical symptoms, serial β-hCG levels, and ultrasound findings.1 The authors of this study found that pseudogestational sacs were a rare finding (2.2%), in contrast to previous literature reporting a rate from 10% to 16%.3 Their main conclusion was that, if an intrauterine fluid collection is seen, it is much more likely to represent an early IUP rather than an ectopic pregnancy. The investigators also were not able to identify a mean sac diameter cut-off that was predictive of ectopic pregnancy. Nevertheless, the largest pseudogestational sac was 13 mm, which is less than the 16 mm cut-off for mean gestational sac diameter that would be suspicious for intrauterine early pregnancy failure if no yolk sac or embryo was visualized.4 Therefore, this study provides support for the premise that, for intrauterine fluid collections of more than 16 mm, the viability of the pregnancy, not the location, is the primary concern.
I find this study to be monumental in that the consequences of mistaking a pseudogestational sac for a real intrauterine gestational sac were drilled into us as OB/GYN trainees. This study indicates that, although a small proportion of women with ectopic pregnancy may have a pseudogestational sac, there are other clinical factors that will be more important in the diagnosis, such as the presence of an adnexal mass, serial β-hCG trends, and diagnostic uterine aspiration. Furthermore, if an intrauterine fluid collection is seen on ultrasound, in the future I will be more reassured that it represents an early intrauterine pregnancy.
REFERENCES
- The American College of Obstetricians and Gynecologists. Tubal ectopic pregnancy, Practice Bulletin Number 193. Published March 2018. https://www.acog.org/clinical/clinical-guidance/practice-bulletin/articles/2018/03/tubal-ectopic-pregnancy
- Phillips CH, Benson CB, Durfee SM, et al. “Pseudogestational sac” and other 1980s-era concepts in early first-trimester ultrasound: Are they still relevant today? J Ultrasound Med 2020;39:1547-1551.
- Benson CB, Doubilet PM, Peters HE, Frates MC. Intrauterine fluid with ectopic pregnancy: A reappraisal. J Ultrasound Med 2013;32:389-393.
- Doubilet PM, Benson CB, Bourne T, et al. Diagnostic criteria for nonviable pregnancy early in the first trimester. N Engl J Med 2013;369:1443-1451.