The menstrual cycle occurs in all females from the onset of puberty (average age of onset 11 or 12 years) and continues until the menopause in middle age. Blood is lost from the uterus via the vagina as the lining of the uterus is shed.
This occurs if it is not needed for a newly fertilized embryo, i.e., the girl or woman is not pregnant.
Menstrual bleeding can last anywhere from two days to seven days. The average length of time between periods is 28 days but this can vary and be anything from 24 to 35 days.
Periods are usually regular so if one turns up two weeks early it can take you by surprise.
Reasons for an early period may include:
If you’re a pre-teen or teenager who has only just started menstruating, you may find that it takes months for your periods to settle down and become regular.
Your method of contraception can affect your menstrual cycle
If you have taken the emergency morning after pill after having unprotected sex, it is designed to bring on your period early. You may also find that after you have taken it, it causes irregular vaginal bleeding. This is one of the side effects.
The regular contraceptive pill can disrupt your cycle
The artificial hormones in it are designed to make your body think it is already pregnant (that is why pregnancy cannot usually occur when you take it).
However, if you’re on a pill-free week and you’ve only just started taking the pill, you may bleed during this week even if the time is different from your usual cycle.
Likewise, if you suddenly stop taking the pill, the drop in hormones may cause you to bleed. If you are using a copper only IUD, this can make you bleed more heavily and have irregular periods.
A sexually transmitted infection can cause bleeding in between periods
You may mistake this for another period. The bleeding is usually lighter than a period.
A sudden loss of a lot of weight or a sudden gain of a lot of weight can disrupt your period
This is because of changing hormonal levels.
Being stressed out can bring on your period early or stop it altogether