My period has been delayed for more than 20 days, and it hasn't come yet.

If a woman's period is delayed for more than 20 days, the first thing to consider is pregnancy. To determine if she is pregnant, she can go to a doctor for an hcg test or use a pregnancy test paper to test herself. If it is not caused by pregnancy, she needs to go to a doctor for hormone level tests and other gynecological tests to confirm the diagnosis.