While it’s possible, having double twins (meaning two eggs split twice) is highly improbable. Identical twins count for just 0.4 percent of all births, or about 1 in 300. The chance of both of those eggs splitting twice is almost unheard of, although there’s been at least one documented case. Note that almost two-thirds of twin births are considered “spontaneous” (natural) while the remaining third come through assisted reproduction technologies like IVF. In that field, doctors are working to get twin and triplet rates down by implanting fewer embryos and cutting back on growing the fertilized eggs to blastocysts before implanting them.
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