Small amounts of free fluid in the pelvis (usually <10 mL but up to ~20 mL near ovulation) can be normal in females (Ritchie, 1986; Hall et al., 1979). This is especially true in patients following ovulation, after menopause, or during early pregnancy. Make sure to look for the free fluid in the Pouch of Douglas.
Here are some pelvic ultrasound images of normal amounts of free fluid in the pouch of Douglas.
