I can say this with near-complete confidence: Never, in the history of fakeouts, has anyone pulled off a fakeout as well as my middle-school sex-ed teacher. We were in the middle of a requisitely awkward discussion of birth-control methods when he dropped the bait: “You know,” he said, “technically — technically — abstinence isn’t the only 100 percent effective way to avoid becoming pregnant.” A pause. Ears perked up. Around the room, hormonal teenagers stopped their doodling and started paying attention. And then he did the switch: “Of course, the other way is already being pregnant, so.” And then, if memory serves, he chuckled.
Well. Joke’s on you, sir. Or really, joke’s on all of us, because the New York Times has busted that myth with a crazy little piece of medical information: Actually, you can get pregnant while already pregnant, a cosmic prank known in scientific terms as “superfetation.”
“Ordinarily, the release of eggs ceases once a woman is pregnant,” the Times wrote in its Science Q&A column, “and the hormonal and physical changes of pregnancy work together to prevent another conception.” But sometimes, for reasons scientists don’t fully understand, the hormones that stop another pregnancy from occurring don’t get the memo about the first one. And even then, as Scientific American has explained, superfetation occurs if and only if a series of “seemingly impossible events” takes place: “Ovulation must take place during an ongoing pregnancy, semen must somehow find its way through the blocked cervix to the oviduct, via the occupied uterus and finally, the conceptus has to successfully implant itself in an unsuspecting already-occupied uterus.”
Which, if that wasn’t already clear, means it’s pretty rare (in humans, at least — as the Times noted, superfetation is fairly common in cats and other mammals). So rare, in fact, that a 2008 paper published in the European Journal of Obstetrics and Gynecology reported that fewer than ten cases had ever been described in the scientific literature — though that number grew by one the following year, when an Arkansas woman named Julia Grovenburg became pregnant with a girl and a boy conceived two weeks apart.
As with twins, superfetation babies are born at the same time, meaning that depending on the length of time between the two conceptions, there’s a risk that a normally timed birth for one baby will be a premature birth for the other. Thankfully, though, both of Grovenburg’s babies were born healthy — and both of them, it’s fair to assume, will grow into kids who can see through at least one of the pranks a slightly diabolical sex-ed teacher may be inclined to pull.