Difficult to know with certainty due to conflicting outcomes in some studies, the quality of others and that we do not know HOW caffeine affects fertility.
Also, conception is only the beginning. The true measure is a live birth.
While more research needs to be done and the evidence is not set in stone: the brief summary is that caffeine appears to affect fertility outcomes in a dose dependant way, and it is NOT just the ovum that looks to be affected….
Despite what the sperm sample findings are, 3 cups of coffee per day (~300 mg/day of caffeine) has been previously described as a risk factor for sperm DNA damage, independent of age (Schmid et al., 2007) and has also been reported to affect Sertoli cell metabolism in a dose‐dependent manner (Dias et al., 2014).
While on the ovum side, of the evidence at hand, some studies have shown that the consumption of less that 1 cup of coffee per day were twice as likely to conceive, another of women using IVF and ART found caffeine to be a risk factor for not achieving a live birth. This study recommended women reduce caffeine intake prior to commencing their IVF or ART treatment.
So how much caffeine is where?
Coffee: Decaf, 3mg, Instant comes in at 60-80mg, a small café coffee somewhere between 113-282mg.
Tea: dose varies depending on brewing time. Black tea, 25-100mg, Green Tea 30-50mg.
Cola 36-48mg and energy drinks, 80mg.
Chocolate you ask. A 100-gram bar has only 20mg of caffeine.
In Summary:
So generally, good advice would be for those finding it challenging to conceive should limit their coffee intake to 1 cup, that is, less than 200mg of caffeine per day.
References:
Male caffeine and alcohol intake in relation to semen parameters and in vitro fertilization outcomes among fertility patients
A. E. Karmon et al
Coffee and caffeine intake and male infertility: a systematic review
Elena Ricci et al
Dose-dependent effects of caffeine in human Sertoli cells metabolism and oxidative profile: relevance for male fertility
Tânia R Dias et al
The Australian Beverage Council
A prospective study of the effects of female and male caffeine consumption on the reproductive endpoints of IVF and gamete intra-Fallopian transfer
H. Klonoff-Cohen, J. Bleha, P. Lam-Kruglick