Two weeks before your period
Your brain’s pituitary gland unloads two fast-acting agents, follicle-stimulating hormone and luteinising hormone, into your bloodstream. Both of them direct-message your ovaries: release the egg!
Message received loud and clear. Your ovaries jettison their most mature egg into a fallopian tube. This isn’t the V8s though – that egg’s journey to the uterus takes 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.
In the next two weeks
As the uterus builds up tissue and blood supply, your ovaries unleash the key pregnancy-supporting hormone, progesterone. Your body temperature may rise a few degrees, though you might not even notice. Other side effects, however, aren’t so subtle… Progesterone also fuels the expansion of the milk ducts in your breasts. Chances are your boobs are now swollen and sore. Some women who are on the pill may be spared this effect.
Progesterone may also interfere with certain brain chemicals, including the mood-regulating hormone serotonin. And it can stimulate the amygdala, a brain structure tied to emotion. The result is two charming PMS calling cards: irritability and anxiety.
Meanwhile, oestrogen and progesterone are also hard at work preparing the womb. Your intestines may relax a bit to make room for a soon-to-be-occupied uterus. As they expand, so do you – yep, we’re talking bloating and gas. Nice. Changes in your insulin sensitivity could also trigger food cravings so you want to eat your weight in banana bread.
As your period starts
That unfertilised egg has waited around long enough, and your uterus senses all the fuss was for nothing. Your oestrogen and progesterone levels plummet, along with – hurray! – most of your PMS symptoms. Your uterine cells begin releasing chemicals called prostaglandins that help slough off the extra blood and tissue. They force your uterine muscles to contract (read: cramps). Inflammatory in nature, prostaglandins can also cause nausea. Thankfully, their production can often be curbed by exercise or anti-inflammatory meds like ibuprofen.
As your period ends
Congratulations, you’ve made it! But ever the optimists, your ovaries start slowly prepping the next egg for release – so the process can begin all over again. Oh joy.