My nanna conceived my mother naturally when she was 39 in the 1940s. This was her first and only successful pregnancy after many miscarriages. I also know of a lady in her forties at work who thought she was starting the menopause and was actually pregnant with twins. She had given up on ever having children but now has healthy twins.
...Another factor to look into: Lunar-ception!!! Some people think it's way out there, but I'm seriously wondering!!! The concept is that as well as being fertile during the obvious times mid-cycle when obvious fertile mucous is present, it is also possible to conceive according to your lunar cycle - that when the moon is at the same phase as when YOU were born, you could have a kind of 'break-through' fertility even if it's at a wierd time of your cycle, and that sex can actually trigger than moon-influenced odd patch of fertility...
This is really interesting. I just checked out my lunar cycle and I was born right on a full moon. After thinking how cool it was to be actually born on a full moon, I recognised that since I have had my ovarian drilling, my mid cycle time cooincides with the full moon. This also happened when I randomly started getting regular periods a couple of years back. I remember this because I have always made a point of looking at the moon to see what it is doing at various points of my cycle because I felt it was more relevant to a natural female cycle than a man-made calendar with man-made dates and prescriptive cycle lengths is. The moon is also female energy. I am going to read more about this lunar conception theory!