Moderate levels of oestrogen have a negative feedback effect on the HPG axis, lowering the amounts of LH and FSH released in order to return the oestrogen back to baseline levels. High levels of oestrogen in the presence of progesterone also have negative feedback on the HPG axis.However, high oestrogen levels in the absence of progesterone exert a positive feedback effect on the HPG axis, causing more LH and FSH to be released.