At the moment, I'm entertained by the thought of asking the details. I bet it's dead boring, though.
Dragons are magical creatures. They may not have sex at all - they may reproduce in a purely magical and spectacular way. They might do it like mammals, or anything. I suspect it might be best for your campaign for you to think about how you _want_ it to work, then let your players try to find out if they're really that interested. It could be quite dangerous uncovering this nugget of wisdom
Personally, I'd go with the 'complete eggs'/chicken style, so if they're stolen they contain an embryo like a chicken egg, which PCs could hatch, or eat, or whatever they desire to do. It's your call, though.