Serial  pelvic ultrasound from about cycle day 10 will show the progression of a growing  preovulatory follicle.  In an un-medicated cycle the follicle will grow at approximately 3 mm/day.  The follicle is presumed to be mature when it reaches 16 mm or larger in diameter, and the woman would likely ovulate within the next several days.  In rare instances the egg, and it associated cells, are visible within the follicle by ultrasound, as in the above photograph.  After ovulation the follicle shrinks in size, and free fluid can be documented in the pelvis.