English: dizygotic twins
Welsh: gefeilliaid deusygotig
Subject: Iechyd
Welsh definition: Two offspring born of the same pregnancy and developed from two ova that were released from the ovary simultaneously and fertilized at the same time. They may be of the same or opposite sex, differ both physically and genetically, and have two separate and distinct placentas and membranes, both amnion and chorion.
Welsh context: Gwelwyd cynnydd sylweddol yn y nifer o achosion o efeilliaid monosygotig (unwy/un ffunud) sy'n cydgordio i drawsnewid o'u cymharu â gefeilliaid deusygotig (deuwy). 
Notes: Mae’r term fraternal twins / gefeilliaid deuwy yn gyfystyr.