MSNBC:

Arkansas couple Todd and Julia Grovenburg found out that they were having a baby and then discovered they were having two bundles of joy — but the babies aren't twins. An ultrasound revealed that a male fetus was conceived a full two-and-a-half weeks after the woman became pregnant with a baby girl, according to reports from local media. The Grovenburgs' obstetrician confirmed the case to Arkansas television station KFSM-TV.

The pregnancy is believed to be a case of a rare condition known as superfetation, or conceiving while pregnant.a

Well, now we know how Sarah Palin did it! Andrew Sullivan has been vindicated.