After bringing him back for the 1992 Animated series under the name Morph ("Changeling" was taken by DC comics for their human/animal shapeshifter), and the comic book adaptation of that series (where he is also killed off), the current version was introduced in 1995 as part of the "Age of Apocalypse" alternate timeline.
Morph is a mimic who can change his appearance to match anyone, male or female, similar to Mystique, who for years was assumed to have been Nightcrawler's mother, but was recently revealed to have been his father (X-Men Blue: Origins #1)
I'm thinking of the mechanics of a shape-shifter being pregnant... like, if they switched genders would the fetus just get stuck inside between organs and die, or would it cease to exist? Would the shape-shifter be able to take on a male outward appearance while maintaining a uterus? Or would they just not shift for 9 months?
Much simpler, I suppose, for the shape-shifter to father a child.