I was going to sleep at 9pm even before I had kids. of course I was waking up for work at like 5am, but still. my wife is younger than me so she took a couple of years before she got to that point, but she's pretty much a homebody too.
I had two different friends who adopted a kid and literally months later got pregnant. my wife was freaking out, but I was pushing restraint hard.
yeah I guess the stress going away or something. or they just jumped the gun. one of my wife's friends has a friend this happened to too. I have no idea if it's common statistically, but it's happened a lot to people I know.
What's so special about her? Put a skimpy dress and a push up bra on a ton of girls and they'll look better than Upton.