At a 7 week scan with ds (done because of previous ectopic) 2 sacs, poles and heartbeats were seen, but about a week different in gestation and the sonographer said that this was a possibility, that I'd ovulated twice and conceived twice. We'd been trying for a baby, so had been having sex every 2 or 3 days.
As it was, one just wasn't growing and had been reabsorbed by the body by 10 weeks. I suppose it's not that weird that, as your body gets older, it tries to up your chances by sending out more eggs.