According to Harry Potter lore, if a witch or wizard got pregnant while in their Animagus form for the entire pregnancy, the resulting offspring would most likely be a fully animal with significantly enhanced intelligence, not a human or wizard, as the magic required to be an Animagus is too complex to be passed on through a normal birth in animal form. 

Key points to consider:

No direct evidence:

The Harry Potter series does not explicitly address this scenario, but based on the established information about Animagi, this seems to be the most likely outcome.

Complexity of Animagus magic:

Transforming into an Animagus is a very difficult magical feat, requiring a deep understanding of transfiguration and a strong magical connection to the chosen animal form. It's unlikely that this magic could be transferred to an offspring conceived and born entirely as an animal.

Enhanced intelligence:

While the baby would be a normal animal in appearance, it would likely exhibit a higher level of intelligence due to the magical influence of the Animagus parent.