The word 生後 means something like "after birth". 明鏡国語辞典 defines it this way:
But 生前 doesn't mean "before birth". Instead, it means something like "before death; while [someone] was still alive". From 明鏡 again:
In fact, 広辞苑 explicitly says it's the opposite of 死後, not of 生後. I find this a bit counterintuitive!
Is there a reason why people say 生前 with this meaning instead of something like 死前? Is there a way to understand it intuitively, or some sort of etymology that makes it make sense? My dictionaries don't explain why 生 + 前 has the meaning 死ぬ前.
Or is it one of those things I should just memorize, perhaps?