As you know, there are two kinds of twins:  identical or one-egg twins, which have the same heredity, and fraternal or two-egg twins, which have different heredity.  Most of the following questions are intended to help determine which kind of twins you have.  Note: The children are referred to as twins, even if they are full or half-siblings. Questions relating to sex or gender refer to the natal or biological sex of the child.

In this form, Twin 1 refers to the first born twin, and Twin 2 refers to the second born twin.