Thanks all for the comments!
I was really worried about the revelation to Lois' parents just as I felt we had so many revelations in this story and I didn't want it to seem repetitive.
To Carol's point, this is very soon to see a baby. I'm sort of making this up from this point as when I had my second ultrasound the gestational sac had grown, but only by about a week to a week and a half in two weeks. The same thing was the case at the next one (although they were sure that the baby wasn't going to make it after the previous one, I just had the last one as I chose to wait for a miscarriage and they need to watch you until it happens). So, I can't be sure what they would say if the baby grew the right amount, but Evelyn's response seemed reasonable to me.
Remember (not that this is going to happen) but even if this was a false alarm or something, the baby is still young and something else could still go wrong, so Evelyn is not going to want to be too positive and make them feel completely secure. While obviously things can go wrong at any time, typical guidance is that once you get to the second trimester your mostly out of the woods. But Lois and Clark are only half way through the first trimester based on the size of the baby.
But gr8shades (and everyone else), I think the next chapter will have a more definitive answer.
Thanks again for the comments, I really appreciate it. Particularly now when I'm making things up and don't have experience to base this on.