Families with twins have unique struggles, like having to buy two cribs, two wardrobes, and change two sets of diapers (that’s a lot of cloth diapers!). It’s a struggle that’s shared by parents of another type of twin: Irish twins.

What Are Irish Twins?

The phrase “Irish twins” describes two children born to the same mother within 12 months.

This phrase originated in the 19th century when many Irish people were immigrating to the U.S. Because the Catholic Church teaches avoidance of birth control, children less than one year apart were common within Irish Catholic immigrant families. Therefore, children with a spacing of less than 12 months became known as Irish twins (also known as “Catholic twins” or “Dutch twins”).

How many months apart are Irish Twins?

The term “Irish twins” refers to siblings who are born within 12 months of one another. This is especially true for children born in the same calendar year, or children who would be in the same grade of school.

However, children born within 18 months of one another are still often referred to as Irish Twins.

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Is the Term “Irish Twins” Derogatory or Offensive?

Most people who use this phrase don’t mean any offense. In fact, many people who fall into this category use Irish twins to describe themselves and their close-in-age siblings.

That said, this term was originally used as a derogatory stereotype of Irish Catholic culture and, therefore, is inherently offensive.

Back in the day, “Irish twins” was a term used to tease Irish immigrant families. It implied that giving birth to children within a short amount of time was a reckless or poor choice.

What Are Irish Triplets?

Irish triplets are three children born to the same woman within a three-year time span. This phrase is also offensive due to its poking fun at Irish Catholic culture.

What is the Shortest Possible Gap Between Siblings?

Because your period comes back after you start ovulating again, you can get pregnant before you get your first postpartum period. This can occur as early as one month after giving birth.

As a result, you can technically have two children who are 9.5 to 10 months apart in age, depending on when you become fertile after giving birth and how long your pregnancy lasts.

Can siblings be born 9 months apart?

It’s possible, but unlikely. Fertility doesn’t usually return until about a month after giving birth (or later), so it’s not likely you will have two children who are only nine months apart. But, if you have a premature delivery with your second pregnancy, it’s possible for your children to be nine months apart (or even less).

Can I get pregnant three months after giving birth?

Yes! If you started ovulating again—something that can happen as early as four weeks after giving birth—you can get pregnant only three months after having your baby. If you think you might be pregnant, the best thing to do is to take a pregnancy test and then check in with your healthcare provider if it’s positive.

Can you get pregnant while you are pregnant?

Typically, when a woman becomes pregnant, the surge in her body’s hormones temporarily prevent’s her ovaries from releasing eggs. Additionally, the mucus plug in the cervix stops sperm from entering the uterus and the uterine lining becomes much thicker, making it difficult for an egg to implant.

In very rare cases something called superfetation can occur—a time when these mechanisms can fail and pregnancy can occur. According to a 2013 review, this most often happens two to three weeks after the first conception. That being said, this is extremely rare—almost nonexistent, really.

Is it Dangerous to Have Irish Twins?

There’s usually no reason to be concerned if you find yourself unexpectedly (or expectedly!) pregnant soon after giving birth.

That said, a 2018 cohort study found that a spacing of 12 to 24 months between pregnancies (not births) was optimal based on research collected from 150,000 Canadian pregnancies.

When spaced closer together, the research indicates that risk factor for adverse maternal and fetal effects increases slightly. Researchers aren’t sure why this is true, but they speculate it may be related to nutritional depletion in mom. Weston A. Price, a dentist who traveled the world studying cultures with the highest longevity rates, found some evidence to support this. He discovered that many of the healthy communities he studied considered it shameful to have children closer than three years apart.

Price explains that this is because these cultures took preconception and pregnancy nutrition very seriously. They prepared the body for pregnancy by feeding men and women a high nutrient diet for at least six months prior to conception. Additionally, they believed it was best to wait about two years before becoming pregnant again. Why? To replenish the nutrients lost through pregnancy.

Are You Expecting Irish Twins?

Congratulations! There’s no reason to be worried. And you certainly shouldn’t feel shame or guilt. Child spacing is ultimately a private choice made within a family and is not something we should decide for other people.

There are many reasons that a family would want to have children closer in age than three years apart (waning fertility, life goals, etc). We’re all on our own journeys and have to make the best choice for our specific situations.

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