test prenatale

If the prenatal test is negative, is it possible anyway that the parent is a gene carrier?

Good morning,
I’ll try to explain myself in the best possible way: my partner's grandfather and mother are affected by Huntington's chorea, but my partner did not want to undergo the test (choice that I respect); now I am pregnant and we managed to do the test on the fetus that was negative to the disease...
My question is: is there any chance that also my partner has not inherited the disease? Or does a one in two possibilities always apply?