What is the incidence of infertility with identical twins?

Answer 1

Most people will answer this by explaining that the twins will run the same risk are normal adults.

However, if the twins are monozygotic they may also be "mirror-twins", in which one twin would have an increased chance of displaying situs inversus, a condition where the organs are flipped (mirrored to other twin).

This in and of itself isn't harmful, but the origins of situs inversus are believed to be in the earliest stages of development, arising from cilia that move clockwise instead of counter-clockwise, thus moving the cells that will form organs to the wrong side.

Going back to questions of infertility, it is known that this wrong-turning cilia cannot play a normal roll in some biologic functions, including driving the bending movement required for sperm (cilia structures of the tail) to be motile. In this way, male infertility (sterility) could theoretically be affecting at a higher incidence in man mirror twins with situs inversus.