We all know that twins are two siblings that were conceived at the same time and born within hours of each other. We know that they share the same birthday, and in some cases even look identical.
But one woman on TikTok has discovered she and her younger brother are actually twins - even though there's a five-year age difference between the two of them.
Anna Hipkin, 19, revealed in a video on her account, @annahipkinxo, that her 13-year-old brother Jack is technically her twin despite their age gap because they were both conceived at the same time, the Daily Star reports.
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In the video, she said: "When you casually get told over lunch by your divorced parents that your 13-year-old brother is actually your twin but you're 19."
Anna's clip left commenters thoroughly confused, so she explained the situation in more detail in a follow-up video, where she said she and her brother were both conceived during the same round of IVF treatment.
But rather than carry twins to term, Anna's mum decided to have one embryo frozen until she was ready for a second child - which happened to be five years after Anna was born.
She said: "I didn't think this many people would be interested, but here I am with the promised storytime. So, as many of you guessed in the comments, we were both conceived through IVF.
"What that means is basically we were both conceived in a dish, and then I was put back in my mum, and then my brother was put in the freezer for five years as an embryo.
"It got to five years of Jack being in the freezer and they were like, 'We'll defrost him'. Fair play to them. They defrosted him, put him back in my mum, and then nine months later, there you go.
"So there are five years between us, I'm 19 and he's 13, nearly 14. Obviously, we're not identical twins, but biologically, technically, we are twins."
Commenters have been divided over the topic, as many people have argued that being conceived from the same round of IVF does not make the siblings twins.
One person said: "How is he your twin?! That's not how it works. He's not your twin!"
While another added: "If you go by that logic, all siblings are twins as long as they have the same parents."
And a third said: "Huh? That doesn't make him your twin though. You have the same relationship as any other siblings. Twins are conceived and carried at the same time."
But others defended Anna, as they shared their own experiences with IVF twins.
Someone said: "One of my friends is the same. Their parents did IVF and had my friend, and then had her twin 10 years later."
As someone else agreed, posting: "Might not be the same but this is me with my brother, he’s 23 and I’m 20 but we’re twins!"
According to research from fertility doctors, women who become pregnant with embryos that were previously frozen tend to have healthier pregnancies with fewer complications than those who have fresh foetuses implanted.
Fertility doctors found out babies born from previously frozen IVF embryos had 16% less risk of being preterm and had a lower risk of dying soon after birth and having a low birth weight.
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