On a flight from Calgary to Tokyo just three weeks later, that blip revealed itself to be a baby bump when the 23-year-old went into labour high above the Pacific Ocean.
A healthy girl was born this weekend to the surprise and jubilation of her unsuspecting first-time parents — and a planeload of passengers aboard an Air Canada flight.
"Had she known she was in her third trimester, she definitely would not have gotten on that plane," said new grandmother Sandra Branch, from her home in Penticton, B.C.
"They were all excited about going and touring Japan, and then this pops out."
Appropriately, baby Chloe Grace arrived on Mother's Day. Her delivery prompted cheers and applause inside the soaring aircraft.
"Everybody was clapping," a brightly smiling woman told TV station FNN News in Japanese, as she disembarked at Narita Airport.
"The baby was so cute. A little girl with big eyes!"
Another passenger said that Guan, 23, was shuttled from economy to business class when she was suddenly struck by dreadful pains.
The flight crew paged for any physicians on board and found a volunteer who tended to Guan for about an hour. The plane landed 30 minutes early after gaining priority from traffic controllers.
Video footage shows air attendants pushing Guan off the plane on a stretcher, followed by her baseball cap-wearing boyfriend. Wesley Branch, 24, stops to wave while carrying the tot swaddled in a white blanket.
"She told me something fell out of me, and I lifted out her pants and I seen a head, and then I heard 'waaa,'" Branch later told Global News from Japan. "I'm like, 'Oh my God, I think we have a kid.'
"It was the biggest surprise of my life."
The new parents, who met while online dating about one year ago, were whisked to a Japanese hospital. By Tuesday they had moved to a nearby hotel because the bill was growing, said Sandra Branch.
They planned to meet with officials from the Canadian Embassy on Wednesday to obtain a birth certificate and other documentation necessary for the journey home.
She said Guan had described on-and-off tummy pains, and even noticed some minor weight gain in the same area. But the couple could only assume the negative test meant she had perhaps miscarried.
"I was in total shock when he called me ... and he said, 'I've got something to tell you mom,'" recalled Sandra Branch.
"He said, 'You're a grandma.' I said, 'What? She wasn't even pregnant.'
"I said to him, 'You probably have a better chance of winning the lottery.'"
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