Are mothers more likely to give birth during a full moon?

Science says “no,” but many nurses aren’t so sure.

Jessica Dulong’s one of those people who seems like she could do anything. She’s an author, a teacher of writing, a post-partum doula, and a marine engineer—meaning she works a fireboat engine. Pretty badass. But in Spring 2012, one thing just wasn’t happening for her. She was pregnant with her son (her only child), and he didn’t seem to want to leave the womb. Thirty nine weeks passed, then 40, then 41 weeks of pregnancy.

“I was more than ready at 41weeks,” she remembers. “It was time, it was really time. But he was not really interested.”

Her pregnancy had started getting scary-long. It was then then, at one of her then almost-daily checkups, a nurse offered what felt like real hope.

“She said, ‘Don’t worry there’s going to be a full moon,'” Dulong recalls. “And she was like, ‘Yeah your baby’s gonna come. And I think I’m on duty, so I’ll see you there, and you’ll go into labor and you know, it will all be great.'”

And the other attending nurse agreed, the full moon is the time for births.

“So they sort of plan it,” Dulong says she was told, “like they kind of know when the full moon is going to be and they brace themselves for what’s going to be a crazy time.”

When asked if she believed them, Dulong says she would have believe anything at that point, she was so eager to give birth.

So, the night of the full moon came. Dulong remembers pacing up and down the stairs of her apartment building, that bright moon shining in. Just hoping the baby would come. But he didn’t.

“Yeah everyone was wrong,” she laughs. “It didn’t go that way, it didn’t go that way at all!”

Instead her fear of having to get induced into labor came true.

Researchers estimate that the majority of nurses and doctors believe in the full moon effect. Eighty percent of nurses, actually. Which makes it a pretty popular topic for research. About once a year someone will do a study about the moon and hospital visits. Most find no relation, but occasionally a study will suggest a slight link between the full moon and medical activity.

Jean-Luc Margot’s an astronomer at UCLA and someone who knows a lot about the moon. And recently he was at a dinner party with a friend of his. She told him the same thing Jessica Dulong had heard about the full moon and births.

“She’s a midwife,” says Margot, “and she was convinced that there were more babies born on the full moon.”

This surprised him. He’d know her a long time, always thought of her as a pretty rational person.

“I told her at the dinner table,” he remembers, “‘You know, surely you must be aware that the numbers don’t support this belief.’ And she was adamant that it was an effect.”

So Margot decided to look into it on his own, to arm himself with information.

“Which I did as soon as I got back to my office,” he says. “I looked at the literature.”

And as expected, most studies said a full moon and a connection with medical events is not a thing. But then there was this one 2004 study that claimed there were a larger number of admissions to a Barcelona hospital unit during the full moon.

“I didn’t want people to walk around with these questionable beliefs in their heads,” he says. “And particularly the fact that the 2004 journal article had not been challenged and was still available in the peer-reviewed literature. I thought something needed to be done.”

So he redid that 2004 Barcelona study. A nursing journal published his work under the title “No Evidence of Purported Lunar Effect on Hospital Admission Rates or Birth Rates.” He found the other researchers had done some pretty shady statistics work. And, they’d gotten the length of the lunar cycle wrong. When he redid their numbers: no link between the lunar cycle and hospital admissions. And no link either when he looked full moons and birth data.

“One of the likely causes for this is something called the confirmation bias,” he says of this belief in the full moon effect.

The confirmation bias phenomenon explains how we’re more likely to notice things that match our expectations. Like say you start to think it always rains when you forget your umbrella. Every time that happens, you’ll note it, theory confirmed. And all the times you forget your umbrella and it doesn’t rain, those don’t give you that little rush of confirmation, so you won’t really notice those times.

“And in the case of the full moon,” Margot explains, “if you happen to see a large number of hospital admissions on the full moon, you will make that association and you will remember it.”

He says he’s not trying to call out nurses, or other medical professionals, as stupid or superstitious. He says we all can be suckers for the confirmation bias. He just wants to set the record straight, so patients in desperate situations like Jessica Dulong don’t get misled.

And of course, he also wanted to disprove his friend from the dinner party.

“I sent her the literature that I found at first,” he says, “and then when I was done writing the paper I sent her a copy of the manuscript. And so we’re still very good friends, you know she laughs about it now, and it’s all good.”

Margot admits his debunking may not always be appreciated. But he’s now a man on a mission. He’s about to come out with a new journal paper that debunks a link between plant pollination and the full moon.