(covers information from several alternate timelines)
Temporal reversion is a phenomenon whereby an organism's cellular structure begins to coalesce, by reverting to an earlier form.
In 2370, the crew of the USS Enterprise NCC-1701-D experienced temporal reversion due to exposure to large amounts of temporal energy being emitted from an anti-time eruption. This had the effect of causing some crewmembers' old scars to heal, the DNA in Lieutenant Commander Geordi La Forge's optic nerves to regenerate, and the death of Nurse Alyssa Ogawa's unborn child, due to the reversion of the embryo's fetal tissue. The timeline in which these events occurred was later negated, however, when Captain Jean-Luc Picard was successfully able to prevent the eruption from occurring in the first place. (TNG: "All Good Things...")