Definition: Mirror image twins are monozygotic, twins that form from a single fertilized egg. When the split occurs late - more than a week after conception - the twins can develop reverse asymmetric features. This term is not really a type of twin, just a way to describe their physical features. For example, they may be right- and left-handed, have birthmarks on opposite sides of their body, or have hair whorls that swirl in opposite directions. In theory, if the twins faced each other, they would appear to be exact reflections of each other. About 25% of identical twins are mirror image twins.
Also Known As: mirror-image twins