Elderling Creations Theory (Spoilers through all the books and Dragon Haven)

[Valarya]

Spoiler

The presumption that elderlings of the stage Reyn/Malta is at cannot have viable children comes from the fact that Tarman had to help it remain alive. As for why tarman knew that? Thats fairly simple... Not even close to all the old era elderlings were born that way. thus it would be natural dragon knowledge that elderlings of certain stages cannot produce live children. In early stages (Jerd, DH), the child becomes more serpent than dragon than human.

Gah, 'thul beings I still completely disagree with you.

CoD spoilers

Just because Tarman knows what to do doesn''t prove it's based on Malta & Reyn's stage-of-Elderling. It only proves that it has happened before, and Tarman knew what to do.

It is YOU theory that it's because of DNA progression in the parents.

It is MY theory that the issue arose due to the fact the child is not fully human, period. And needs to be touched by a dragon. I believe that child would be changed no matter what "stage" malta & reyn are at in their Elderling-changes.

---------

Spoiler

One thing 'thul do wonder about is how long the periods of gestation are in Elderlings and dragons. Obviously eggs aren't laid instantly after mating. Considering how suddenly Malta's birthing came upon her and how (relatively) easy it was, the period of gestation is probably shorter than it is for humans. Shorter gestation typically means smaller infants. The potential presence of claws also supports this as a good idea.

I think you're going way off track with this, but that's just my opinion.