How much free fluid can a pregnant patient have? Assessment of pelvic free fluid in pregnant patients without antecedent trauma.

BACKGROUND: The amount of free fluid that can normally be present in a pregnant patient is unknown. Evaluation of pelvic free fluid in a population of pregnant patients without early history of trauma would help determine what amount of free fluid should raise suspicion of intra-abdominal injury in those who have suffered trauma.

METHODS: Patients presenting for routine obstetric ultrasound without an early history of trauma were offered participation in the study. Routine imaging of the cul de sac and ovaries was used for assessment of presence or absence of free fluid, with accompanying digitally recorded images. Depth of the fluid pocket was measured in millimeters.

RESULTS: Six of 89 patients successfully scanned were found to have free fluid in to the cul de sac for an occurrence of 6.7%. Four patients had free fluid present during the first trimester with subsequent resolution by the late first trimester or early second trimester. Two of these patients had an identifiable cause for free fluid, one with right ovarian hyperstimulation and the second with idiopathic theca lutein cysts. Two patients had isolated free fluid appearing in the third trimester.

CONCLUSIONS: These results suggest that the presence of pelvic free fluid in pregnant patients without antecedent trauma is very low. After blunt abdominal trauma, the presence of free fluid in the pelvis of a pregnant patient may not be physiologic, especially if there is >2 mm to 4 mm, and there is no history of ovarian hyperstimulation syndrome or other known associations.