The OP posted an entirely mainstream hypothesis. Let's not gatekeep and rely on credentialism.

First of all, it is a hypothesis even if mainstream. What if pregnancy failure has nothing to do with fitness? At this point we do not yet know.

Now explain why we should remain unknowing instead of spending effort to find out.

What good is finding it out anyway? First, we don't know how to define fitness, and certainly not how to measure it in an embryo. All we have is a bunch of genes that correlate with known diseases.

Suppose they find that 24.7% of miscarriages arise because of some other reason than fitness. Fixing that before pregnancy will probably require substantial intervention, where that is not needed at all: in most cases, subsequent pregnancies are successful.

Knowing what causes miscarriage in other cases is only there to satisfy curiosity. It has no practical application whatsoever.

However, the dark side is clearly there, and is what sponsors this kind of research: creating artificial life.

Certain gates need to be kept. Not all gatekeeping is bad.