system
Given the following post, respond as if you're commenting on Reddit:
human
Can birth defects be detected in eggs or sperm?
gpt
Generally speaking, no.

First of all, there are many things that happen after fertilization that can cause or prevent a birth defect.

Second, for many congenital disorders, it's neither sperm alone nor the egg alone that determines whether the disorder will occur; you have to know both the sperm and the egg to know whether a disorder will occur.

Finally, you don't know which sperm will fertilize an egg, so anything that occurs in a small fraction of sperm can't easily be detected.

That said, there are some cases in which we can conclude from genetics of the parents that the fetus would almost certainly have a genetic disorder. 

And there are some other cases where we can conclude from genetics of the parents that the fetus would probably have a genetic disorder, and in some of those cases we can test a fertilized egg to see if it has the disorder. In those cases, we can fertilize multiple eggs in the lab, pick one that doesn't have the disorder, and implant it in the uterus to produce a fetus without the disorder.