In the realm of freaky pregnancies, it’s hard to top a scenario that could have come straight out of an episode of I Didn’t Know I Was Pregnant. But this one deserves an honorable mention: a woman who conceived a baby while she was already pregnant, only to give birth to the “twins” with two separate due dates.It’s the kind of thing you’re told simply doesn’t happen, but it happened to 39-year-old Rebecca Roberts, who was struggling with infertility for over a year before she finally became pregnant. She and her partner were overjoyed at the first ultrasound appointment, but the second was unexpected. The Washington Post reports that the English couple was shocked when the 12-week ultrasound appointment showed that Roberts was carrying another—less-developed—baby.From the Washington Post, emphasis ours:But this wasn’t a typical set of twins, Roberts learned. Her pregnancy was diagnosed as superfetation, a rare condition in which a woman who is already pregnant conceives another baby.Roberts’s pregnancy is one of very few superfetation cases recorded in medical literature, her obstetrician, David Walker, said.Superfetation is so uncommon, in fact, that Walker struggled to diagnose it at first. In his 25 years as an obstetrician, it was something he had never seen before.“It just doesn’t happen,” Walker said, adding that it took several scans before he could confidently diagnose the condition.[…]Ordinarily, hormonal and physical changes during pregnancy prevent another conception from occurring. That wasn’t the case for Roberts.“Instead of stopping ovulation, she released another egg about three or four weeks after the first one, and the egg somehow miraculously managed to fertilize and implant in her uterus,” Walker said.G/O Media may get a commissionThe extra baby was a welcome surprise, but the complications that came along with it were not. Superfetation is rare, and the younger twin usually doesn’t make it. About 33 weeks into the pregnancy, the umbilical cord for the younger twin wasn’t working, and a C-section was performed to prevent any further obstacles. So on September 17, Roberts gave birth to Noah—the older, bigger twin—and Rosalie—the younger, smaller, surprise twin. The twins were kept in a neonatal intensive care unit, Noah for three weeks, Rosalie for 95 days. But now, the twins have been home for several months and are happy and healthy.And, yes, the age difference is obvious. Check out this recent Instagram post featuring the twins:As the couple told the Post:“Even though they were born on the same day, there’s definitely an age difference between them,” [Roberts] added. “It’s noticeable.”Rosalie is still much smaller and less advanced than her brother, “but she’s catching up to him fast,” said [Rhys] Weaver, a mortgage adviser.Bodies, man.