There are many medical reasons for a possible enlarged liver. I don't even know if a doctor can sort through the reasons "why".
The regular doctor probably didn't even want to speculate.

I think if we even try to guess, it's walking on dangerous ground because this is a question for a highly trained specialist. I am so glad you guys are going to a high risk doctor. I currently see one and the ultrasounds are wondering. The specialist is highly trained in situations like you are experiencing and will be able to tell you more. I know this answer doesn't help ease your anxiety of "not knowing" at the moment. It may turn out to be nothing, you never know. I am impressed that your doctor was able to determine what he or she did. Kuddos to that doctor and also kuddos that he or she referred you guys to a specialist.