(YouTube / NBC News)

Call it a baby bump.

Nine nurses at a Maine hospital are pregnant and expecting children within a four-month range this spring and summer. And they all work in the hospital’s labor and delivery unit.

“Throughout the shift, we’d name the people [who were pregnant], and we were like so and so, so and so, and so and so,” one of the pregnant nurses at Maine Medical Center in Portland told NBC on Monday. “Then we got to two hands and were like, Whoa!”

The story went viral after one of the pregnant nurses, Brittney Verville, posted a photo on Facebook of eight of the women lined up outside the unit they work in, holding cards with their due dates.

“Something is definitely in the water here at Maine Medical Center on the Labor and Delivery Unit!” she wrote. “Lots of baby friends being made this summer!”

The hospital followed by reposting the picture. “How’s this for a baby boom?” the hospital wrote. “Congratulations!”

Carol Sakala, who runs maternal health and maternity care programming at the National Partnership for Women & Families, said there was probably not a scientific explanation for the baby boom.

“I don’t know of any biological reason for this,” she said. “I was trying to think of possible reasons for a cluster — sometimes sisters and close friends enjoy going through the child rearing and bearing experience together.”

Sakala said that the photo made her wonder about the maternity leave policies available to the women.

The hospital declined to comment through spokeswoman Caroline Cornish, who said that the nurses were resting: “the ones who aren’t working, that is.”

There are 80 registered nurses working in the hospital’s labor and delivery unit, the outlet reported. The hospital told some expectant mothers who said they were worried about the hospital’s staffing needs that everything was going to be fine.

“It’s comforting knowing we’ll be taking care of each other,” Samantha Giglio, one of the nurses who’s expecting, told News Center Maine.

“I’m curious if there will be any L&D nursing staff at MMC when I deliver at the end of June,” one wrote.

“Don’t worry!” the hospital responded. “We have a plan.”

Last year, 16 nurses at an Arizona hospital were pregnant simultaneously. They all worked in the intensive-care unit.

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