Hooooooo boy… Not asking any easy questions, eh?
Alright, remember how I talked about genetic mutation back here? No? Alright, well, the important bit was how mutant humans had such a jumble of DNA that mutations can readily appear and are often stable. That same variety also allows mutant humans to breed with other species, leading to individuals with the Hybrid Edge.

Hybrid mutants are almost always born to mutant human females with males of other species, but the inverse isn’t impossible… Merely very uncommon. In general, the hybrids tend to appear more human than their male parentage’s species, but some features are bound to bleed through into the offspring: changes to skin or hair, musculature and height, abnormal teeth length, or any other prominent features from the father’s species are likely.
So, if a mutant human, female, player character has a penchant for boinking mutant plants, there is a chance that she’ll end up carrying a baby with green skin and leaves for hair. Do I have rules for it? No. Will I be including a brief entry in the GM’s guide to handle situations when a PC wants to run a character pregnancy? Probably.
If I were cornered by my players who wanted to play out a pregnancy right now, I would probably have some Endurance checks be rolled with minor DCs and then ask them to describe what their characters do during the intervening months/years. From there, child NPCs…
Was going to find a good, meme-y picture to wrap this up, but I also don’t want to do a google search for “half-breed mutant child.” Instead, have some related Krieger.