Are Irish Twins Really Twins?

Irish Twins. altrendo images / Getty Images

Are Irish twins really twins? The easy answer is “no”. The technical answer is “no”. But the reality of the answer is, “Well, they could be.” or “So close, they might as well be.”

What are Irish Twins?

Irish twins are described as two children born to the same mother in the same calendar year or within twelve months of each other. For example, a mother gives birth to a boy on January 2, 2013, conceives another child on February 15, 2013, and delivers another boy on December 28, 2013.

The brothers would be considered Irish twins.

Sometimes the term is stretched to include siblings born in close succession, such as 15 or 16 months apart. 

The term originated the 1800’s and wasn’t always intended as a nice description of a close family. But in modern times, it’s more generally used to refer to kids who are very close in age. 

Are Irish Twins Actually Twins?

If you use a dictionary to define a twin, you’ll find two types of descriptions. The first is quite literal: “either of two children brought forth at a birth” ( or “either one of two babies that are born at the same time to the same mother.” (Merriam-Webster) 

By that definition, Irish twins are not twins. Twins are two children born from the same conception, carried during the same pregnancy, and born together. 

But because of reproductive and medical technology, one can put forth examples of all kinds of exceptions that violate that definition but still produce individuals that would still be considered twins.

What about in-vitro twins or cases of frozen embryos? How about a delayed interval birth, where twins have different birthdays, being born days or even weeks apart? (Here's a literal case of Irish twins, twin sisters from Waterford, Ireland who were born 87 days apart, at 23 weeks and 36 weeks. They hold the Guinness World Record for the longest interval between the birth of twins.)

Are Irish Twins a Type of Twins?

A more liberal interpretation of the definition of twins is “either of two persons or things closely related to or closely resembling each other” ( or “either one of two similar things that form a pair” (Merriam-Webster). For those that want to make the argument that Irish twins are a type twins, these definitions seem to apply.

But the fact is, having two children close in age is simply not the same as having twins. Twins, even in those cases where they’re born apart, are same-age siblings. Irish twins are separated in age by at least a few months. Even considering the most extreme scenario -- getting pregnant again at the first possible opportunity after giving birth, then delivering the second baby prematurely -- a pregnancy gestation requires a period of months to produce another offspring. 

Both parents of twins and parents of closely-spaced children have much to add to the debate over which circumstances are more challenging. But most will agree that having twins is not the same as having Irish Twins. One or the other may be easier or more difficult, but they’re not the same thing.

Some of the issues of raising Irish twins may be similar to what parents of twins face.

Two in diapers at the same time. Two cribs, two high chairs, the need for a double stroller. Sometimes, Irish twins can even end up in the same grade at school. They may have the same friends, enjoy the same activities, and generally live a similar lifestyle as they grow older, much in the way that twins would.

Arguably, the experience is more diverse with younger children. A newborn and a ten-month-old baby have vastly divergent developmental capacities. Yet, a nine-year-old and a soon-to-be ten-year-old may not appear quite so distinct. As puberty approaches, the differences may become more pronounced, then less distinguishable as the children grow up.


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