Poppy and Piran House were born at 34 weeks after parents Jennifer Ashwood and Andrew House found out she had a rare “heart-shaped” uterus.
Remarkably, she became pregnant with twins when one egg was released into each uterus and they were both successfully fertilized at the same time.
Doctors told the family the chances of having twins in this way was one in 500 million.
The family, including 8-year-old Millie, are now all home in Camborne, England, getting to grips with their two new members.
Jennifer, a care coordinator, said: “To have the two uteri is rare in itself, but to have an egg in both, then those to be fertilized, and then for both eggs to be in the right part, it’s a bit of a miracle.
“It is ridiculously rare. The odds were stacked against us but it all worked out. You think that you know your body well, but it turns out you might not.
“I’m 31. I’ve had a baby before and it was really straightforward. But my body has surprised me this time.
“It’s two separate uterine cavities joined by one cervix. Everything else is the same, with two fallopian tubes, one each side, each with an ovary.
“It’s caused by a midline abnormality from when I was in the womb.
“What happened was at the time of ovulation an egg was released from each tube, one into each uterus, and both were fertilized, and both remained in each uterus.
“It’s crazy when you think about it. It’s possible that the fertilization could have occurred one or even two days apart, but it was at the same time.
“We found out at the 20-week scan and ever since people have been saying how rare it was.”
Jennifer and Andrew, a firefighter, found out they were expecting twins in December 2017 and he proposed on New Year’s Eve.
In January 2018, they found out she had a uterine abnormality and doctors revealed in February she had a complete bicornuate uterus with a baby in each side.
A bicornuate womb is heart-shaped and women have no extra difficulties with conception, but there is a slightly higher risk of miscarriage and preterm birth.
In most cases, women with the condition will only carry one baby in one uterus.
Jennifer went into early labor at 28 weeks, but her contractions were stopped with medicine, and she had a C-section on May 6.
Piran was born first at 5 pounds, 10 ounces, with Poppy born minutes later weighing 5 pounds 3 ounces.
Doctors even took a photo of Jennifer’s uterus during surgery at her request so she could see what it looked like.
Jennifer was allowed home after five days, while the twins stayed in the hospital for two weeks, having jaundice treatment and feeding support.