A Louisiana couple welcomed spontaneous triplets – a rare occurrence that happens to 1 out of ever one million to 200 million pregnancies.

Haley and Charles H. SloanMatthew Cordaro gave birth to the special trio at Willis-Knighton South & the Center for Women’s Health in late August, the hospital said in a Friday press release. The trio was conceived naturally.

Claire, Ella and Lily Codaro were born prematurely at just 31 weeks and have been at the hospital since their birth. Doctors anticipate that they'll be able to go home sometime this week.

“They have done very well. It has been a straightforward and uncomplicated stay,” Dr. Gerald Brent Whitton, a NICU doctor who has been taking care of them said. “As we get closer to the babies’ release, we will get the parents up here and get them used to taking care of all three at the same time.”

The triplets have a 3-year-old sister named Kennedy, and are the first set of multiples on both side of their family.

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What are spontaneous triplets

Spontaneous triplets is a term used to refer to identical triplets that are naturally conceived. While the probability of conceiving triplets naturally, is around one in every 10,000 pregnancy, the odds of those twins being identical is at least a one in a million chance.

Pregnancies of multiples like twins and triplets do occur naturally, but experts have said they've seen the rate of these pregnancies rise with the help of fertility treatments, The Washington Post reported.

So, naturally conceived identical triplets where one fertilized egg splits three times, or it splits twice, and one of those two embryos splits again, are very, very rare. There's also no way to really predict if someone will have this type of multiples, or any way to increase the likelihood of this type of pregnancy.