Five sets of twins started at Wairarapa College this year in a quintupled double whammy for the school that would be difficult to match.

Assistant principal Aaron Perkins said multiple birth students were in abundant supply at the college and, besides the virtual flood of Year 9 twins, also included a twin brother and sister who were both prefects, and a sibling from a set of triplets who was likewise a prefect.

"The Year 9 twins get on very, very well together and seem to know what the other one will say and how they're feeling, you know, like finishing sentences for each other and that sort of thing."

Mr Perkins said he had not seen so many twins populating a single year group before and he was pleased the sets of siblings had found their way to Wairarapa College.

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The Rose sisters said their classmates were so far still flummoxed as to who was who of the two of them, although twin brother and sister TJ and Ariana Sutton said most people were a little disbelieving when told the pair are twins.

Three of the sets of twins, they say, had been born two minutes apart and of each pair first-born were Shana Beneke, Danielle Rose and Ella Southey, while Ariana Sutton beat her brother to the punch by eight minutes and Danielle Mason led her sister by nine minutes.

According to the Kiwi Families website, twins and triplets are becoming increasingly common in New Zealand.

Twin births naturally occur in about one in every 100 pregnancies, the website continues, but the rate has increased due to in vitro fertilisation. Triplets and other multiple births, such as quads and quintuplets are "an extremely rare natural occurrence, with triplets only occurring naturally in 1 in 8000 pregnancies".

A rapid search online revealed that twins can be conceived by two different fathers -- common in dogs and cats but extremely rare in humans -- and identical twins may share DNA, but exposure to different areas of the womb during development affects the fingertip ridges and whorls.

Also, twins sometimes develop cryptophasia, a language exclusive to each set of twins that to others is simply babble. Twins are believed to begin interacting in the womb as early as 14 weeks into pregnancy.