Congenital birth defects are a large field, and hundreds of rare conditions exist.  A few lesser-known conditions that appear more often in historical records include anencephaly and hermaphrodism.  Anencephaly occurs when the fetal brain fails to fully develop.  This condition is incompatible with life.  A hermaphrodite is an individual with external and possible internal male and female genitalia.  Today, operations can assign a single gender to an individual.4

Conjoined twins are traditionally included in discussions of birth abnormalities.  Twins differ based upon where they are attached.