Definition - What does Withdrawal Bleeding mean?
Withdrawal bleeding refers to the bleeding that occurs in response to a drop in hormones. This is what is referred to as menstruation (or a period) when a woman is on oral contraceptives or hormones. Natural menstruation is the monthly (or cyclic) shedding of the uterine lining. When a woman is on hormonal contraceptives the uterine lining remains thin. There is no physiological need for withdrawal bleeding to occur. However, when hormones drop such as in the hormone free week of hormonal contraceptives, the body responds as it would a natural menstrual cycle.
Winthdrawl bleeding shouldn't be confused with breakthrough or mid-cycle bleeding, where bleeding occurs while under persistent hormal use.
FertilitySmarts explains Withdrawal Bleeding
Withdrawal bleeding may differ in how long and when it starts to occur depending on the hormonal contraceptive or hormonal replacement that is being used. It feels like a natural menstrual period even though it is prompted by hormone withdrawal rather than an attempt to shed the uterine lining.
Hormonal contraceptives are used to prevent natural fluctuations of hormone levels which cause the uterine lining to thicken in order to prepare for fertilization and implantation as well as cause an egg to be released. Hormonal contraceptives keep the uterine lining thin and prevent ovulation from occurring. Since there is no physiological need to have withdrawal bleeding while on hormonal contraceptives, some women skip the hormone free week to forego the bleeding.
Fertility is still prevented even during the menstrual week when using hormonal contraceptives. This is because the uterine lining remains low and ovulation was still prevented assuming accurate use of the hormonal method.