What percent of people are twins at early stages in the womb?
There’s some research on this question (the “vanishing twin” effect) but no hard answers. Some research puts the early twinning rate at 1 in 8, but others have found much lower rates with early ultrasound. In any event, of the fetuses that survive to term or near-term, the identical twin rate worldwide is about 4 in 1000, while the fraternal twin rate is about 28 in 1000. There are significant differences between mothers of different ethnic groups and ages. There is also a genetic predisposition to have fraternal twins that is passed down through the maternal side. As for the association between a vanishing twin and being born left-handed, this is only one of many theories and beliefs about the causes of left-handedness.
