Rebecca Oldham had three scans, two blood tests, and six pregnancy tests to determine the cause of her stomach pain, but it wasn’t until doctors cut her open during surgery that the true root of the problem was discovered: a 36-weeks, 9-pound baby boy.

Oldham, 25, was resigned to the idea that she would never be able to become pregnant again. The New Zealand native was scheduled to have her ovaries removed in order to alleviate the painful cramps she had suffered for months.

"I was facing not being able to have any more children because they thought there were problems with my ovaries and all of a sudden we had a son," Oldham told The New Zealand Herald.

To the shock of everyone in the operating room, the surgeon found a living, fully developed human fetus inside Oldham.

The surgeon waited until Oldham was awake before informing her that the operation was changing to an emergency Caesarean section and that she would shortly be the mother to a newborn baby boy. Although shocked by the news, Oldham was glad she at least had a bit of notice before becoming a mother again.

"I am so glad they woke me and told me I was going to have another baby. Even though it was short notice, it was better than waking up and being handed a baby," Oldham explained to The New Zealand Herald.

Unsure How Baby Went Undetected

Doctors are calling Oldham’s case extremely rare. The baby was able to avoid detection due to an out of the ordinary positioning inside his mother. "He was lodged in, even with the Caesarean they had to use forceps to get him out," Oldham said.

The baby was found lodged tightly along his mother’s back, and this is what doctors believe had caused Oldham’s painful cramps.

Still, although take-at-home pregnancy tests will often give false readings, according to Auckland obstetrician Dr. Martin Sowter, the positive pregnancy results should have revealed themselves on the hospital blood test.

"After eight or nine weeks there will always be some pregnancy hormone floating around," Sowter told The New Zealand Herald.

As for the being undetected in the scans, Sowter describes that this only ever happens in extremely overweight or obese women, of which Oldham is neither.

“The only way you might miss that is if you were looking at the wrong scan or if the person doing the scan didn't know how to use the equipment properly," Sowter added. Oldham and her boyfriend and father of the baby, James Tipene, hope an investigation of how the pregnancy was missed will provide them with some more answers.

Happens 'About Once A Year'

Oldham’s case is rare but not isolated. Patrick O’Brien, a consultant obstetrician at University College Longon Hospitals told the BBC that he sees a case where a woman doesn’t realize she’s pregnant until very late stages about “once a year.”

According to O’Brien, factors such as a woman having a history of infrequent period and being overweight will sometimes mask the obvious signs of pregnancy.

"Sometimes, if all these things coincide, they can be unaware," O’Brien told the BBC, but in his opinion, it's most common for teenage girls in denial about their pregnancies to be unaware.