These two South Jersey sisters have Leap Day birthdays — and so does the doctor who delivered them

If you thought sharing with your siblings was torture, imagine having to share your birthday. Even worse? If your birthday only comes every four years.

Welcome to the lives of Chloe and Joelle Davidson, sisters who were born on Leap Day 2012 and 2016, respectively. Chloe is celebrating her official birthday for the second time ever Saturday, turning 8 years old. Blowing out the candles next to her will be her youngest sister, Joelle, who is turning 4 — her first official birthday.

“It’s really special,” said Chloe, the third youngest of eight children in the Davidson clan. “But sometimes it gets annoying."

The crazy coincidences for this Haddon Heights family don’t end there. On Thursday, Chloe and Joelle reunited with Eric Grossman, the ob-gyn who delivered both girls. He was born on Feb. 29, 1972.

The girls, accompanied by their mom, Jamie, gathered at the maternity wing of Virtua Hospital in Voorhees on Thursday, and gave Grossman handmade birthday cards for any babies who are born Saturday. Yes, he will work on his special day.

“I love working on my birthday,” said Grossman, a doctor at Advocare Premier, a private practice that primarily works out of Virtua. “It’s a special birthday, and it’s almost like bringing them into a little club."

All the leapers in that club are statistical oddities: There’s a 1 in 1,461 chance of being born on Leap Day.

But what are the odds of being in a situation like the Davidsons and Grossman? We asked Robin Pemantle, a University of Pennsylvania professor of mathematics, about the probability of their coincidence.

He said that under a set of assumptions — that the date wasn’t planned and the children were born naturally — for a couple with only two children, the probability that two children were born on a Leap Day is about 1 in 2.1 million. Because the Davidsons have eight children, the probability of having two leaplings increases — about 1 in 130,000 families with eight children would have a pair of Leap Day children.

Bringing Grossman into the picture makes it more difficult.

To estimate the probability of this level of coincidence, you’d have to have a lot more detail on the circumstances of the delivery and the number of people present. Ignoring those issues, the probability that two out of eight kids plus the doctor would all have leap day birthdays would be just under 1 in 100 million.

(Don’t even get us started on the fact that Jamie Davidson and her husband, Josh, are both identical twins.)

There is, of course, a slight hitch to these big numbers. Chloe’s and Joelle’s birthdays aren’t complete coincidences. Chloe was due on Feb. 25, and once that day passed, the doctor gave Jamie dates to induce. She chose Feb. 29. Joelle was originally due on St. Patrick’s Day but Davidson had high blood pressure, so Joelle needed to be induced during her 37th week, and the 29th fell during that window.

Davidson nearly had three kids on a Leap Day. Her fourth son, Caleb, who will soon be 12, was due on Feb. 27, and she was hoping he would come on the 29th. He arrived March 4, 2008.

If Caleb had arrived 96 hours earlier, the Davidson family would have tied the Guinness world record for Most Siblings Born on a Leap Day. The record, which has been matched by a few families since, is held by the Henriksen family of Norway, which logged Feb. 29 births in 1960, 1964, and 1968.

Chloe said she loves her birthday, but does get sick of the mundane joke that she’s “only 2 years old.”

“It gets old,” she said.

But that didn’t stop her from taking advantage of the big day. She got to invite her whole class to her party, which was themed “Terrible Twos.” When it’s not a leap year, she swaps between Feb. 28 and March 1.

Grossman, who has delivered four of the Davidson children and lives in Cherry Hill, said he never gets tired of the birthday jokes. While he technically turns 48 Saturday, he welcomes the theory of only being 12. When he was younger, his birthday was a two-day celebration. Now, his birthdays are often still kid-themed, like bowling, but “with an adult twist."

Chloe, according to a Virtua spokesperson, was the first girl leaper born at the hospital, which had opened just three years prior. On Feb. 29, 2016, when Jamie had Joelle, eight babies were born at Virtua Voorhees.

Walking through the maternity wing Thursday brought back a rush of nostalgia for Jamie Davidson.

“Usually when I’m here," she said to her daughters, “I’m having you guys.”