A married couple discovered they were biological twins after getting a routine DNA test at an IVF clinic because they were struggling to conceive naturally.
The couple, who met in college, had attended the clinic in Mississippi in the hope that it would be able to help them have their own child.
But instead the doctor was forced to tell the shocked pair that they were brother and sister.
"During the process we take a DNA sample from both the male and female to get a profile of their genetic backgrounds", the doctor, whose name has been withheld to protect the patients’ identities, told the Mississippi Herald.
“It's just a routine thing and we wouldn't normally check to see if there was a relationship between the two samples, but in this case the lab assistant involved was shocked by the similarity of each profile.”
The doctor said his initial reaction was that they might be first cousins, which he said “happens sometimes” but then he noticed the very close similarities.
He checked the patient file and saw they had the same birthdays listed in the same year – 1984.
He then realised the husband and wife must be biological twins but did not know if they were already aware.
“It was a difficult subject to raise,” he said. “They burst out laughing when I asked them if they were twins.
“The husband said a lot of people remarked on the fact they shared the same birthday and looked similar but they said it was just a funny coincident and they were definitely not related.
The doctor says he continued to insist that the pair were twins and had DNA evidence to back it up, after which the wife "pleaded" with him to admit he was joking.
"I wish that I was, but they had to know the truth," he said.
The couple had met in college and hit it off due to their similar backgrounds – they had both been adopted after their parents had died.
The pair’s biological parents had died in a car crash and, due to a filing error, neither of their adopted families were told they had a twin.
According to the doctor, the husband and wife are now considering their future together but are thought to be exempt from facing criminal charges for incest due to the unusual nature of their case.