Possible twist at the end of CoE
The introduction of the "Hitch-hiker" at the beginning of episode 1 and Gwen later mentioning to the your doctor that "anyone could be carrying one" seems like a bit of a set up.
II wouldn't put it past the writing team to reveal that Gwen's "baby" is actually a hitch-hiker alien. For one thing Clement's psychic ability might not register it as an alien, merely new life. And the scanner simply registered a new organism inside Gwen. Nothing specifically saying it was a gestating foetus.
Just a thought.