Intrauterine fluid with ectopic pregnancy: a reappraisal.

Objectives-To determine the incidence of intrauterine fluid in patients with ectopic pregnancy and to define the characteristics that distinguish this fluid from an early intrauterine gestational sac. Methods-We identified all patients scanned transvaginally at our institution from July 2008 through August 2011 for suspected ectopic pregnancy, who proved to have ectopic pregnancy based on pathologic, surgical, or adnexal sonographic findings. We reviewed the sonograms to characterize any fluid in the uterus as to shape, contents, and location. Fluid was classified as type A if it was pointy edged, contained echoes, and/or was clearly located within the uterine cavity or type B if it was smooth walled and anechoic and location was in the decidua or uncertain. The appearance of type A fluid is inconsistent with a gestational sac, while the appearance of type B overlaps that of a gestational sac. Results-Our study population included 229 women with ectopic pregnancy. In 38 (16.6%), sonography showed fluid in the uterus, which was classified as type A in 31 and type B in 7. Only 2 patients (0.9%) had type B fluid with no adnexal findings suggestive of ectopic pregnancy. Based on these results and the published incidence of ectopic pregnancy (2% of all pregnancies), we calculated that a patient with a positive pregnancy test, an intrauterine smooth-walled anechoic cystic structure, and no adnexal mass has a 0.02% probability of ectopic pregnancy, while the probability of intrauterine pregnancy in such a patient is 99.98%. Conclusions-Fluid can be seen in the uterus in 16.6% of patients with ectopic pregnancy. On transvaginal sonography, it can be distinguished from an early intrauterine gestational sac based on shape, contents, and/or location in most cases. In the remaining cases, the fluid appears indistinguishable from, and is highly likely to represent, an early intrauterine gestation.