Periods are caused by hormones cycling between the brain and the female reproductive organs.
They’re called cycles because they usually happen every 3-5 weeks… But they’re not always predictable, especially for the first several months (or even years).
Image Source: University of California at San Francisco
The brain sends hormones to the ovaries and uterus, signaling the ovaries to ripen an egg and telling the uterus to build up a lining in preparation for that egg.
Ovulation means the release of an egg from an ovary.
An unfertilized egg leaves the ovary, passes through the fallopian tube and through the uterus.
Once the egg leaves the body, hormone levels drop and the lining of the uterus sheds off.
The chart above shows how the hormones rise and fall, telling the ovaries and uterus what to do.
If you have an extra 4 minutes, watch this TED-Ed video on hormones and the menstrual cycle.
REGULAR VS. IRREGULAR
The term “cycle” can be misleading because periods don’t always happen at regular or predictable intervals.
Periods can be regular or irregular.
Being regular means getting a period at a predictable time — usually every 3, 4, or 5 weeks.
Beingirregularmeans periods come sooner or later than expected.
Both of these patterns can be totally normal at first!
It can take months or even years after the first period before cycles become regular.
If you have an extra 5 minutes, watch this video on irregular periods from NHS 24.
