A couple trying for a baby for nine years have defied odds of 70 million to one to produce quadruplet daughters from a single IVF embryo.
Christine and Justin Clark, from Rotherham, started IVF treatment last year after trying to conceive naturally.
A single embryo was implanted and Christine found out she was pregnant three weeks later.
The girls - Darcy, Caroline, Elisha and Alexis - were born by caesarean section at Sheffield's Jessop Hospital for Women on March 25, weighing just over 10lbs between them.
They are now being cared for in the Special Care Baby Unit at Rotherham Hospital.
Christine, 36, a nurse, said: "When we found out we were having four babies, I just couldn't believe it.
"I was speechless when the doctors told me. We were hoping for one child but four was unbelievable. To be honest, I didn't believe it until I saw them for myself."
Justin, 43, a lorry driver, said: "They are the first set of quads to be born from a single embryo, which was then split into three. One of these three then split into two, to make twins. That makes our children very special.
"When the children were born there were two placentas so we're not sure yet if we have two babies and the twins, or triplets and a single child.
"We have been told tests will have to be carried out when they are 10 to 12 weeks old to confirm this."
Adel Shaker, medical director at the CARE Fertility clinic in Sheffield, who treated Christine on the NHS, said: "I have been working in IVF for over 20 years and this is the first case I am aware of where a single embryo transferred resulted in a quadruplet pregnancy.
"I have seen two embryos transferred resulting in triplets and a single embryo resulting in twins. Even those pregnancies are very unlikely.
"Previous IVF quadruplets have seen babies from both sexes and were reported after transferring two embryos at least.
"This is to my knowledge, the first time a quadruplet pregnancy is reported after a single embryo transfer and all the babies are of the same sex."
Christine added: "We'd been trying for nine years to have one child and had no luck. We had given up but we talked it over and decided to try IVF treatment.
"It was a very emotional time for us when we were told we were going to have four babies. We were happy, but at the same time we were also worried about the logistics of how we were going to bring them up.
"The girls are all doing well and we have been able to take one of our daughters, Alexis, for her first walk in a pram. It was the first time either of us had pushed a pram and it was a wonderful experience.
"Now we can't wait to get them home.It will be a very special day in our lives when that happens. It's heartbreaking leaving them at the hospital but fortunately we know they are in wonderful hands."
Doctors are hoping the babies can go home next month.