Birth of twins unrelated to each other or to their gestational mother

This report records the first documented instance of a birth in which twins, genetically unrelated to each other, were born to a mother genetically unrelated to either of them. After an extensive history of infertility with multiple unsuccessful treatments, a 42-year-old woman gave birth to healthy twins following transfer of three embryos from two different donor sources. DNA testing confirmed that the twins represented both sources. This report adds to the growing body of literature documenting the successes of embryo donation to other couples, and supports the option of embryo mixing for those couples who wish to consider it.