I have to preface this by saying I have identical twins, so I have some skin in the game as they say. You may find this completely dull.
I know this doesn’t really matter for anyone other than the twins themselves, but I’m finding it crazy how many twins identify as “non-identical” (fraternal) when they’re clearly identical. There seems to be a long standing misunderstanding about what makes twins identical even amongst doctors and sonographers (who are usually the ones who have the first conversation with the parents when they ask).
The common misconception seems to be that if the babies have a placenta each, they’re not identical, but that just means the egg split early enough in the process for them to grow their own placentas.
I have worked with a set of identical twins (completely identical by sight) who had never had a DNA test and swore blind they weren’t identical because their mum had asked and the doctor confirmed they aren’t, but they clearly were. There’s a saying in the twin mum world that if 90% of people can’t tell your twins apart, there’s a very strong likelihood they’re identical. I’ve seen it a few times now where people don’t seem to wonder why no one can tell their “non-ID” twins apart.
Why does this matter? Well, it’s a huge advantage knowing your twin shares your DNA if you’re ever gravely unwell. And also it’s just interesting (to me anyway!).
I’ve attached a picture of the Olson twins - clearly identical but reports still say they aren’t. It seems so common that people accept the misinformation still.