<P> Premenstrual water retention (or premenstrual fluid retention) is a common phenomenon associated with the menstrual cycle . It consists of the retention of water during the period of time immediately preceding the menstrual cycle (that is, the latter half of the luteal phase, or the week before menstruation). This water retention is most noticeable for its temporary enlargement of the breasts . The excess fluid is lost during menstruation . During this event, the water retention can store enough extra fluid to add an extra 5--6 pounds (2.3--2.7 kg) of weight . The phenomenon is thought to be caused by high levels of circulating progesterone, as well as of estrogen and prolactin, stimulating secretory cells in the body and in the breasts . In the breasts, increased blood flow is also thought to be involved . Water retention and breast swelling can also be caused by hormonal contraceptives (which contain estrogen and / or a progestogen). </P> <P> According to three studies, fluid retention is not premenstrual, but rather peaks on the first day of menstrual flow . It also does not appear to be correlated to serum levels of progesterone or estrodial . Fluid retention is higher in recreational runners as compared to "normally active" women . </P>

When does water retention occur during menstrual cycle
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