We do get a description of what Voldemort's body was like after Wormtail's clumsy care, but before the regeneration proper:
It was as though Wormtail had flipped over a stone, and revealed something ugly, slimy and blind - but worse, a hundred times worse. The thing Wormtail had been carrying had the shape of a crouched human child, except that Harry had never seen anything less like a child. It was hairless and scaly-looking, a dark, raw, reddish black. Its arms and legs were thin and feeble, and its face - no child alive ever had a face like that - was flat and snake-like, with gleaming red eyes.
Harry Potter and the Goblet of Fire - pp.555-6 - Bloomsbury - Chapter 32, Flesh, Blood and Bone
And there's nothing really to suggest it was a human fetus. Voldemort is also capable of talking and holding a wand, which would surely be beyond the physical capabilities of a fetus that wasn't developed enough to show. And if Bertha Jorkins was showing, I feel her pregnancy would've been remarked on in the books - because it would have been very relevant to her not reappearing.
All in all, I think it's just a fan theory - I don't believe you'll find anything in canon to confirm it, or even offer tentative support. That said, that would be to be expected if it was really not suitable for the audience and really, really unpleasant.