The Menstrual Cycle

Between days six and twelve the developing egg releases increasing amounts of oestrogen which #1 makes the endometrium thicken #2 eventually reaches a level which tells the pituitary gland to release luteinising hormone (LH). #3 reduces the production of FSH which causes a drop in oestrogen production. #4 days thirteen to fourteen LH peaks this stimulates ovulation then the LH makes cells grow in the space where the egg was (corpus luteum) and the cells release progesterone. Days fifteen to twenty four progesterone maintains the endometrium and increases its blood supply. It inhibits the production of FSH and LH. Days twenty five to twenty eight the low level of LH allows the corpus luteum to break down it no longer makes progesterone and the next period starts. If the egg is fertilised and implants the corpus luteum goes on producing   progesterone until the placenta is developed enough to make its own the high levels of progesterone prevent the endometrium and the developing baby from being shed. The progesterone only mini pill and contraceptive injection and implants make your body think you are pregnant so no egg is released.