Victoria Lasita and her husband Tim conceived both sets naturally, without fertility treatments that increase the chance of multiple pregnancies.
"Holy smokes. Do you know what the odds of that are?" fertility expert Dr Glen Hofmann told the Cincinnati Enquirer.
The chances of conceiving one set of triplets naturally were about one in 8,000, making the odds of having them twice about one in 64 million, he said.
Having triplets once did not affect the chances of having triplets a second time, added Dr Hofmann, medical director of the Bethesda Center for Reproductive Health and Fertility.
Casey Alexander was the first born at 1357 local time on Wednesday at just 4lb 2.5oz (about 1.9kg).
He was followed by Caden Bradley, at 4lb 13.5oz (about 2.2kg) and Carson Charles, at 4lb 9.5oz (just over 2kg).
Their father, Tim, who witnessed the Caesarean birth, said: "Everybody seems to be doing well."
He said it was still too early to know when the babies will be ready to go home and join their older siblings, Jessica, Jillian and Brian, who will soon turn four.
The Lasitas have been married six years and have three grown children from previous marriages.
But they decided they'd like "one more" after the birth of the triplets.
"I guess we should have been more specific and said one more child, not one more set," Victoria said.
The Lasitas will be changing about 150 nappies a week for the new triplets.
Victoria said: "You take what God gives you. And this is what he's decided we can handle."
Last Mod: 02 Eylül 2007, 13:20