What medical reason for this question before a prenatal untrasound?

Factual Questions
1

Back in 1999, when my wife was pregnant with our first child, we went in for an ultrasound. Most of the questions had an obvious medical reason, but one left me stumped. Just remembered it today.

The questions that made sense:
Any prior full-term pregnancies?
Any prior miscarriages?
Any prior terminated pregnancies (i.e. abortions)?
How many?

And then the stumper:
(Pointing at me): Same father?

Is there some legitimate medical reason to know who was the sperm donor on the previous aborted pregnancy? (it wasn’t me, it was before we met)

2

I’m guessing it’s something about RH factor. Unlike other blood type factors, it’s safe for an RH- person to be exposed to RH+ blood… once. But after that, they’ll have developed a sensitivity to it, and the second exposure can cause serious problems. And since a fetus and the mother can have different RH types, this can cause problems with pregnancy.

At least, that’s the gist of it. I probably have some of the details wrong.