On fertility after 40

I read this quote from Slate Magazine with great interest.

Did Elizabeth Edwards use donor eggs? – By Suz Redfearn – Slate Magazine: “‘The probability [that she used donor eggs] is 99.9 percent,’ said David Adamson, a Palo Alto, Calif.-based reproductive endocrinologist and clinical professor at Stanford University’s School of Medicine. ‘If she hadn’t, she’d probably say, ‘No, I didn’t use donor eggs.’ ‘ Adamson, who sits on the medical advisory board of RESOLVE: The National Infertility Association, added that in the 25 years he’s spent treating thousands of infertility patients, he’s only seen one woman of 45 and one of 46 give birth using their own eggs. Fecundity starts to drop off long before that, he says. At 35, one in four women trying to have a baby will run into difficulties. At 40, about half will fail to conceive naturally. Above 45, there are so few births using one’s own eggs that no one keeps records of it, said Adamson. When it happens, you’re in miracle territory. “


I was thinking of me and my friends in our traditional, Catholic homeshooling group. I know quite a few women who have had babies over 40. I have had four pregnancies and three babies after 35, and two pregnancies and one live birth after 40, one of those was after 45. I also have two friends who had babies at 48 and 49 respectively. I’m wondering if there is a sociological explanation for this as well as physiologic. In other words, are women in monogamous married relationships who have been open to life throughout their marriages more apt to be fertile later in life? I wonder.