Please read the update notes, Parasite Worms eat eggs and trigger the Big Worm scene, birth scenes are only available for the other 4 critters.
If you want a full incubation, get rid of the parasites first :).
- Progress is the progress to birth (or Big Worm scene in case of Parasite Worms).
- Egg count is explanatory, number of eggs inside.
- Fullness is how much full she is. It is calculated based on everything else.