Identical twins Amanda Caston and Julia Baldree weren't expecting to give birth on the same day, but fate had other plans.

The 27-year-old sisters gave birth within the same hour on March 28, according to NBC affiliate WBIR-TV.

Caston, a teacher, tells PEOPLE she was due to deliver son Miles on April 2, while her sister was expecting her twin boys, Josiah and Carter, to arrive on April 22.

But even when they learned that they were going to welcome their children early, they had no idea that they'd give birth on the same day. 

"I was not expecting that at all," Caston says.

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Caston was induced one week early on the 27th, but didn't deliver until the next day — the same day Baldree had her cesarean section. 

"When he got here at 10:24 a.m. on Monday morning, I was waiting to hear from my sister," says Caston. "And then I found out they were all born within an hour."

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According to WBIR-TV, a New Jersey mathematics professor said the odds of identical twins giving birth on the same day, with one twin welcoming another set of twins, are around 4 in 100,000.

Caston tells PEOPLE was impressed by the numbers. "I thought that was crazy," she says.

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Neither sister ever expected to have their own set of twins, so the fact that Baldree did is "mind blowing."

"It's been really fun and definitely an adventure," Caston shares. "And we're excited that they get to share birthdays just like we did." 

She adds, "So it worked out really good, and we're all really excited."