In some women the flow is lost from the uterus in a variable continuous discharge through the cervix, but in the majority it is lost in ‘gushes’ of varying volume. It seems that the uterine cavity tends to fill with blood, fluid, and cell debris while the myometrium is relaxed, and then when a contraction occurs, the contents are expelled into the vagina. Transvaginal ultrasound 9 can give a valuable picture of the changes in blood in the uterine cavity, if timed appropriately. Mostly, these little gushes are of a volume around 0.5-1 ml, but in women with excessive bleeding we have measured, on ultrasound scan, a uterine cavity volume of up to 28.5 ml immediately before a uterine contraction, and a ‘large gush’ around the vaginal
ultrasound probe. These gushes are presumably mainly responsible for the ‘accidents’ and ‘floodings’ which women with excessive bleeding commonly report. A sudden uterine contraction expelling a volume of around 30 ml will be a substantial test of the absorbent quality of the best and largest menstrual pads and tampons! This phenomenon is the assumed cause of what the menstrual hygiene product manufacturers rather quaintly call ‘product failure’! Repeated ‘accidents’ and ‘floodings’ of this type appear to be significant contributors to a woman's perception of her menstrual loss as heavy, or exceedingly heavy.