What’s going on during that hellish period prelude Two weeks before your PMS period • Your brain’s pituitary gland unloads two fast-acting agents, follicle-stimulating hormone and luteinising hormone, into your bloodstream. Both direct message your ovaries: Drop the package! • Message received. Your ovaries jettison their most mature egg into a fallopian tube. This isn’t NASCAR, though; that egg’s journey to the uterus will take a few days. • In the meantime, your ovaries ramp up oestrogen production. The hormone signals the lining of your uterus to start building a suitable home for an embryo.