What is the effect of caffeine on fertility?

Usually not much: It seems to be dose dependent such that only at very high amounts can caffeine affect fertility. But caffeine can be in different foods and drinks so sometimes people don't realize how much caffeine they consume. But certainly 1 cup of coffee or tea per day should not have any effect.

Variable: Remember this. Millions or women who drink coffee get pregnant. If it's not happening for you, besides exploring other factors, it wouldn't hurt to change up your lifestyle, if it's ok with you. Would it be hardship for you to temporarily quit caffeine for 10 months? If not, then you can try it. However, you would still be better off exploring other factors. Good luck!

Moderation!: As always, moderation is unlikely to lead to any major problems. Many ivf centers recommend minimal caffeine intake during attempted cycles, however the effect if any is small. Very high caffeine consumption (as a marker of psychosocial stressors?) is associated with increased pregnancy loss.