i think around 20% of women have irregular cycles.

i've heard that that can be one reason why women are prescribed the pill. it regulates your cycle, basically. after some time of taking that... i think that people can stop taking it and their cycles are regular.

weight can have a lot to do with it... if your BMI is low (and / or if you are very atheletic) then that can result in irregular cycles. stress...

there would also be the possibility of ovarian cysts (which are very common and also treatable), hormone regulation (also treatible with hormone replacement / the pill).

http://patients.uptodate.com/topic.a...=endocrin/9299