A husband and wife who were trying to conceive received the shock of their lives after being told they are biological twins.

In a freakish twist, the couple, who had both been adopted after their parents were killed in a car crash as infants, found out the news after giving DNA samples prior to an in vitro fertilisation procedure.

A report from the Mississippi Herald said the couple thought the doctor was joking at first, then realised the horrible truth.

The identity of the couple has been withheld due to patient confidentiality restrictions.

"It's just a routine thing, and normally we wouldn't 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.

The couple, who met at university, acknowledged that they did share similar backgrounds, however they said these similarities were what drew them closer.

"The fact that they'd both been adopted, after their parents had died, meant they'd both experienced a similar childhood and they felt they could really connect with each other. If they had only known the truth, it could have saved them so much pain later on."

The couple is currently assessing the future of the relationship.