When reaching max size, there's nothing that happens until you decide to give birth. But I think it would be nice for something more to happen. When your overdue, your belly grows slightly. for every instance it would've progressed normally. Everytime the character commenting on how there feeling fuller, and fuller, there belly getting redder and redder until they reach a limit, where they will have a 'divine burst' where they'll pop. The seeds would either be lost or reduced in numbers.
This could be a toggled feature, as not everyone might like that.