Cervical mucus during the days of menstrual
flow is invisible amidst the blood
. Following menstrual
flow, the mucus
is small in amount, thick, non-stretchable. Under the influence of estrogen, the mucus increases its content of salt and water: thus, it becomes thin, runny, stretchable and remains so until ovulation. Following the egg release, progesterone causes the mucus to have less salt and water: thus it is thick, tacky, poorly stretchable.