There were zero reports I've heard from any TV, movie, or comic reference to the snap of unborn (but possibly viable) babies being left behind (by any species even) when the pregnant mother disappeared in the snap. That suggests the Infinity Gauntlet doesn't consider the unborn as a separate individual until birth.

And da babies in-utero? Did the Infinity Gauntlet go by conception or 24-weeks?

Now you got this idea in my head, if it would have been possible to know if the Infinity Gauntlet considered conception, couldn't a species, lets say humans, knowing "the snap" was a possible risk, create massive stores of zygotes kept on ice? Lets say 10 zygotes to every 1 living human. After the snap of "half" that would mean that instead of 50% of humans disappearing it would only have been 2.5%.

Moreover, since every other species would have lost 50% and been in chaos it would have been prime opportunity to conquer other species still in disarray.

I'm aware ;)

The scientific definition of life changes constantly, but viruses more often than not fall under "not alive."

Throughout, viruses have rarely been considered alive. More than 120 definitions of life exist today, and most require metabolism, a set of chemical reactions that produce energy. Viruses do not metabolize. They also don’t fit some other common criteria. They do not have cells. They cannot reproduce independently. Viruses are inert packages of DNA or RNA that cannot replicate without a host cell.

Source

Eh, it's not really that cut and dry. You could debate either way with plenty of evidence, in the end it's really a limit to the semantics of language

Edit: here's a neat article that talks about it