Of all the things you might expect to hear during a pregnancy ultrasound, being told there is a bonus baby hanging out in your uterus definitely isn't one of them.
For Rebecca Roberts, from England, she still hasn't overcome the shock of being told she had fallen pregnant - while pregnant.
The 39-year-old at first appeared to have a textbook pregnancy. All was progressing smoothly when she had her first dating scan, where she was told she was carrying a 'singleton'.
Fast forward to her 12 week scan and the jolting silence from the sonographer alerted Roberts and her partner Rhys Weaver that something was going on.
Due to a case of superfetation - where a woman can fall pregnant from an egg released during a following menstrual cycle, she was now expecting two babies.
The statistical miracle is so rare there have only been a few known cases recorded in medical history. For the majority of women, hormones would prevent ovulating while pregnant.
"It was really, really shocking to be told there were two babies instead of one," Roberts told Good Morning America.
"Then they told me there was a three-week size difference between the two babies that the doctors couldn't understand."
As her obstetrician David Walker told WAPO, not even he could believe it at first.
Roberts' pregnancy is one of few superfetation cases recorded in medical literature, said her obstetrician, David Walker.
"It just doesn't happen," he said.
"We were concerned because the second twin was much smaller. It was only by regularly scanning and seeing that the rate of growth was consistently three weeks behind that we realised it was superfetation."
Both babies appeared to be healthy and were growing at a good rate, however due to the three week gap, the focus was initially to keep Roberts pregnant as long as possible, to allow the smaller twin more time to develop.
However complications in her third trimester meant doctors decided to deliver the twins at 33 weeks, delivering both by Caesarean on September 17.
The older twin, Noah, was born weighing roughly 1.8 kilos, while his younger sister Rosalie weighed just 1.2 kilos.
While Noah spent three weeks in the NICU, Rosalie spent 95 days, and was given the all clear to join the family, which also includes Roberts' 15-year-old daughter, in time for Christmas.
"They're my super twins," Roberts told GMA. "Every day I look at them and think, 'Wow, I'm so lucky.'"
"I wanted another child for years and years and years and I waited for the right guy to come along and then I met Rhys and we fell in love and we wanted a baby and we were trying for ages to have one and we couldn't get pregnant."
"Then we got pregnant and were blessed with two babies. It's like, wow, this was worth waiting for."
The couple are also documenting their journey on Instagram.
"We want people to be able to continue to watch as they grow up," said Roberts. "Miracles can happen, and my children are proof of that."