It's not as easy to tell with cresteds as it is with leos but not impossible. You can usually see their eggs as a buldge on the side of their body if they move just right or if you look closely. You can't see them through their belly like leos.best way is to weigh them and they will weigh more when they have eggs.

Also no, it is not true that a female's first clutch is ALWAYS infertile. But the first year is usually not the best for cresties. I have heard a 50% hatch rate is pretty normal but I had three females on their first year last year with one on her 2nd and although my girl on her second had a very high hatch rate the other girls did rather well too, more like a 75-80 hatch rate. So, I guess I would say it depends on the gecko. But that is just my experience with them.