[pseudocoup]

From reading it appears all parties are invested in the outcome of children. So this becomes interesting for other reasons.

What is the current state of the art in this type of testing? Why is a definitive result too far off but also too expensive?

[PaulKeeble]

Epigenetic changes might be one possibility, they are sometimes passed down to children and are responses to environmental adjustments. We don't know most of the rules around them however nor what can be passed down and to what extent but potentially in the future we should know more.

[muskstinks]

You need to find a genome change if it exists which requires whole genome sequencing. so its a money question and doesn't guarantee a result

[giantg2]

And even if a genome change exists, it may not show up in the offspring depending on which version of gamete they're derived from.

[GeekyBear]

With identical twins, the genome is identical since both twins derive from the same fertilized egg.

I'm not sure how future advancements can overcome that issue.

[muskstinks]

There can be very small mutation which you might be able to find if it happened.