Your gynecologist or fertility specialist may report that an ultrasound has detected free fluid in your cul-de-sac area. This is an area just behind the vagina. Learn the different causes and concerns about this finding.

Location of the Cul-de-Sac

There are two small pouches close to the uterus, one on either side, called the cul-de-sacs.

The anterior cul-de-sac is located between the bladder and the uterus. The posterior cul-de-sac is found between the uterus and the rectum. They are also called the excavatio recto-uterina (posterior) and excavatio vesico-uterina (anterior).

Another term for cul-de-sacs is Pouch of Douglas, named after the Scottish anatomist James Douglas.

Finding Fluid in the Cul-de-Sac in Fertility Treatment

In women undergoing fertility treatment, fluid in the cul-de-sac (as seen on ultrasound) is a common finding in ovarian hyperstimulation syndrome (OHSS). If the doctor suspects that you have this condition, he will likely suggest that you have an ultrasound to check for fluid and measure your ovaries, as enlarged ovaries are also common in OHSS. Usually, fluid in the cul-de-sac is not a cause for alarm but could be causing discomfort and affecting your fertility.

Causes of Fluid in Cul-de-Sac

Fluid in the cul-de-sac can be caused by many different factors. Sometimes fluid from a ruptured cyst or follicle can accumulate there. At other times, fluid in the cul-de-sac could indicate more severe problems. Here are some possible causes of fluid in the cul-de-sac:

Retrograde menstruation
Increased ovarian permeability due to estrogen influence
Uterine fibroids
Endometriosis
Ectopic pregnancy
Uterine rupture
Ovarian torsion
Pelvic inflammatory disease
Tubo-ovarian abscess
Pelvic abscess or hematoma
Gross ascites
Following culdocentesis
Hydatiform mole

Diagnostic Testing of Free Fluid in the Cul-de-Sac

Transvaginal ultrasound is the procedure that is used to show whether there is fluid behind the uterus. Fluid will show up well on ultrasound. If fluid is found in your cul-de-sac and you are experiencing pain, your doctor may order more advanced testing of the fluid.

Culdocentesis is a procedure performed to check any abnormal fluid in the cul-de-sac area. Before transvaginal ultrasound became widely available, it was also used to detect the fluid. Now, it is used to remove fluid to evaluate.

Culdocentesis involves inserting a needle through the vaginal wall to draw off a sample of fluid to analyze. A numbing agent or anesthesia may be used prior to the procedure. You will have a pelvic exam and your health care provider will hold the cervix with an instrument to insert the needle in the correct place.

A small amount of fluid in the cul-de-sac is normal and is usually not of concern. If the fluid sample shows signs of pus or blood, the area may need to be drained. Sometimes blood can be a result of ruptured cyst or signs of an ectopic pregnancy. The presence of pus could indicate an infection caused by a tear or other conditions. The blood would need to be drained and antibiotics used to treat the infection.