The case could have been straight out of an episode from "I Didn't Know I Was Pregnant": Stephanie Jaegers, 37, went to the doctor for what she believed to be kidney stones only to learn that she was 38 weeks and two days pregnant, and already in labor. Surprisingly, the symptoms of kidney stones and labor are quite similar, and undetected pregnancies, also known as cryptic pregnancies, are more common than you might think.

Jaegers, of Atlanta Georgia, visited the doctors due to her mild back aches and painful urination, which she attributed to kidney stones, The Washington Post reported. However, a blood and urine test revealed that the mother-of-three was not suffering from kidney stones, but was in fact already in labor. The child, Shaun Jude Jaegers, was born perfectly healthy despite his mother having no idea she was even carrying him.

Cases such as Jaegers are known as cryptic pregnancies, and they are far more common than you might expect. For example, according to Lifestyle.com, about one in 450 women do not realize they are pregnant until about the 20th week (which in most cases is more than halfway through the pregnancy).

However, how did Jaegers who already carried and delivered two boys and a girl prior to Shaun’s birth, confuse labor contractions with kidney stone pain? According to the Mayo Clinic, some of the most symptoms of kidney stones include severe pain in the side or back which can spread to the lower abdomen, pain in urination, and nausea and vomiting. Still, it’s likely that it was the combination of both the lack of pregnancy symptoms, such as Jaeger having little weight gain and still having a menstrual period, and its similarities to kidney stones, that led her to misdiagnose her condition.

According to The Washington Post, the baby was sitting behind a rib, which is why Jaegers never felt him move and why she did not develop a prominent “pregnancy” belly. In addition, doctors explained her lack of classic pregnancy symptoms as a result of hormone imbalances caused by her being premenopausal. Still, although Shaun’s birth was a surprise, his parents are no less excited about his arrival.

“It was scary for a second,” Jaegers explained, as reported by The Washington Post. “But we're lucky and thankful that it turned out the way it did.”

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