Rhiannon and Natalie Perllman traded places in the maternity suite when one was wheeled out after having her twins as the other was wheeled in.
The coincidence happened despite the fact that Rhiannon, 23, and Natalie, 27, were supposed to give birth more than a month apart.
But Natalie's twins, Finlaye and Riley, were born at 9.50am and 10.14am respectively on March 17, nearly four weeks early. Rhiannon's daughter Ellen came along just after midday the next day, 10 days late.
Ellen weighed in at 6lbs, 10oz while Finlaye was 5lbs, 3oz and Riley 5lbs, 11oz.
Natalie was being taken out of the suite at Norfolk and Norwich University Hospital as Rhiannon was brought in.
As you can imagine, neither of them were in much of a state at the time to exchange pleasantries as they were whisked by each other!
"All the family are already talking about how we are going to celebrate their 18th birthdays - and it will be great for family get-togethers, as the children are virtually the same age," says Natalie. "We cannot wait for family barbecues."
The delighted mum-of-two added: "It was a really special weekend and we wanted to record it by having our pictures in the paper."
Natalie spent seven days in hospital after giving birth and Rhiannon three days, so their time overlapped.
The sisters were able to enjoy each other's company for a while together in the hospital's Blakeney ward.
Natalie's partner, Charles Moore, 28, says: "It just seems really bizarre. None of it was pre-planned. But we would like to thank the staff at the hospital who were amazing. They were a credit to the NHS and to humanity."
The family already has a bit of a history of babies being born in the same month or on the same day.
The sisters' brother Matthew and other sister Eleanor were both born on April 3, but nine years apart, and Natalie and Rhiannon were also both born in December, Natalie on the 18th and Rhiannon on the sixth.
Have you got a birth story to rival Natalie and Rhiannon's?
More on Parentdish: Sisters give birth within hours of each other in the same hospital!