Our studies have found that parents or twins who were incorrect in their assumptions of zygosity were incorrect because of wrong advice by parents or medical professionals, or by their own incorrect assumptions (Cutler et al. 2015).
Some of the myths that exist around twin zygosity are:

• All same-sex twins are identical
• All twins with separate placentas are fraternal
• All IVF-conceived twins are fraternal
• Identical twins must look exactly alike