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(NEWSER)– Twins are rare, occurring in roughly 2% of all pregnancies. Of those, monoamniotic twins—in which the babies share both a placenta and amniotic sac—are even more uncommon, happening in fewer than 1% of all instances of twins. But what makes an Iowa woman's pregnancy absolutely singular is that she was pregnant with monoamniotic twins without knowing it.

As WHOTV reports, Shelby Magnani was having stomach pains, particularly a "sharp pain" on her left, so she went to a walk-in clinic. "They said we think you might be pregnant," she tells the station. "They told me I was six months and told me to get down to the ER" for an ultrasound. That's when the Ankeny woman and fiance James Croskey learned it was twins.

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