N.J. SISTERS, OB-GYN HAVE LEAP DAY BIRTHDAYS

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 celebrated her official birthday for the second time ever Saturday, turning 8 years old. Blowing out the candles next to her was her youngest sister, Joelle, who turned 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. Last week, Chloe and Joelle reunited with Eric Grossman, the ob-gyn who delivered both girls. He was born Feb. 29, 1972.

The girls, accompanied by their mom, Jamie, gathered at the maternity wing of Virtua Hospital in Voorhees on

Feb. 27, and gave Grossman handmade birthday cards for any babies born Feb. 29.

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?

Robin Pemantle, a University of Pennsylvania professor of mathematics, 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 Feb. 25, and once that day passed, the doctor gave Jamie dates to induce. She chose Feb. 29. Joelle was originally due 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.