The term “fluid dark zone” usually refers to the presence of blisters seen under ultrasound, which are called fluid dark zones because the fluid within the blisters is relatively uniform. However, the meaning of a dark fluid zone can vary greatly depending on the specific location of the zone. If the dark area is on the ovary, it may be a physiologically dominant follicle or it may be an abnormal ovarian cyst. If the dark area of fluid is localized to the cervix, it is considered to be caused by a cervical nuchal cyst. If the woman’s fluid dark area is in the uterine cavity and pregnancy has been confirmed by blood HCG, it temporarily means that a gestational sac has appeared in the uterine cavity. This is due to the short duration of menopause, which is why we see just a simple liquid dark area and no yolk sac has appeared yet.