New Jersey mom Michelle Birnbaum celebrates her real birthday for only the eighth time today.

And the guest of honor at her party will be another very special birthday girl — her 4-year-old daughter, Rose, who remarkably beat the 2 million-to-1 odds and also was born on Feb. 29.

Birnbaum, 32, who lives in Saddle River, insisted that as delighted as she is to finally have a built-in party partner, she never planned to create two generations of Leap Year birthdays.

She went into labor on Feb. 28, 2008, but Rose didn’t make her grand entrance for another 11 hours, as the calendar flipped to Feb. 29.

“It was just luck, all the stars lined up at the right time,” said Birnbaum, a lawyer for kids in child-welfare cases.

As a kid, Birnbaum said, birthdays were always a two-day treat, spanning Feb. 28 though March 1.

Birnbaum hopes to use their Feb. 29 birthdays as a hook for science lessons, to help Rose learn about Earth’s annual trip around the sun that takes a little more than 365 days to complete.

Rose was among 11,430 babies born in the United States on Feb. 29, 2008, according to the National Center of Health Statistics.

There were 3.61 million US births in all of 2008.

Mom Birnbuam was one of 4.24 million U.S. babies born in 1980, but the NCHS had no readily available data to show how many came into the world on Feb. 29 that year.

Brushing aside huge variables such as seasonal birth rates, specific generational trends, and other man-made manipulations, the odds of a mom and child sharing Leap Day birthdays are 1 in 2.1 million, according to James Ennis, a professor at Tufts University.

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