Knowing medical risks can be helpful, if the intent is to be prepared in advance for helping a child that may have special needs as the result of a hereditary health issue. This is as long as the couple do not use the results as an excuse to use artificial contraception. That’s where things get morally hazardous. Another potential problem (hypothetically speaking) would be if state or medical authorities were to pressure the couple into getting tested with the intent of then pressuring them not to conceive—or worse, using legal force to prevent it.
It would also be wrong for friends/family/society to denounce them as irresponsible if they conceive after getting a positive result back for genes linked to disease.
You’d probably get a more nuanced response to this question by posting in the “Ask an Apologist” section, or seeking info from the National Catholic Bioethics Center (ncbcenter.org/ ) or Human Life International’s Truth and Charity forum (truthandcharityforum.org/)