What are the reasons that someones menstrual cycle can change?

Question

I started my cycle when I was nine, so I have been getting it for 15 yrs now. For the first 10 years it was every 30 days, then for the next two years it was every 33 days, then for the next year it was 35 days, then for the next year it was 37 days, and for the last six months it has been at 40 days. I have never had an abnormal pap smear, and I have 2 children, but they were both conceived when my cycle was still every 33 days, I am only 24, does fertility start declining this early?

Answer 1

It basically goes back to the early days--caveman days I guess. You ovulate once per cycle and the closer your cycles are the more chances per year to get pregnant. Younger women were most able to carry a baby and care for it so as a woman ages and has children her biological need has been met and she doesn't need to ovulate as often--basically she's done her part to contribute to the gene pool.