Is it normal for your girlfriend's menstrual cycle to be only about 20 days?

Patient's question:

No

Doctor's answer:

The menstrual cycle is usually between 28-30 days, with a delay or advancement of about one week still considered within the normal range. The length of the cycle also varies from person to person. As long as the menstrual cycle is regular, even if it shortens to 20 days or extends to 45 days, it is still considered a normal phenomenon.