Advice to cut caffeine while trying to conceive is close to universal, and it is usually given without a number attached or a study behind it. The underlying research is better than its reputation suggests, and in one important respect it is better designed than most nutrition research, because one study measured caffeine in blood rather than trusting people to remember what they drank. This article covers what those studies found for women trying to conceive and for men's semen quality, and it deliberately stops at conception, since caffeine during pregnancy is a separate question with a separate answer.
What fecundability means
Studies of trying to conceive do not usually report whether people got pregnant, because almost everyone does eventually. They report fecundability, the probability of conceiving in a given menstrual cycle, expressed as a fecundability ratio or odds ratio. A ratio of 1 means no difference, below 1 means taking longer, above 1 means conceiving faster. This is the right measure because it captures delay rather than only failure, and delay is what most couples experience and worry about.
The study that measured caffeine instead of asking about it
The standing problem with this literature is that people are poor at recalling caffeine intake, cup sizes vary enormously, and how fast a person metabolises caffeine differs genetically. Purdue-Smithe and colleagues[1] got around that. Working within the EAGeR trial, they followed 1,228 women aged 18 to 40 with a history of one or two pregnancy losses, and measured caffeine, paraxanthine and theobromine in 1,191 preconception serum samples, alongside self-reported beverage intake.
At baseline, 85% had detectable serum caffeine, 73% paraxanthine and 91% theobromine. During up to 6 cycles of follow-up, 797 women became pregnant. After adjustment, none of the three metabolites was associated with fecundability: comparing the highest to the lowest third, the odds ratios were 0.87 for caffeine, 0.92 for paraxanthine and 1.15 for theobromine, all with intervals comfortably crossing 1. Self-reported intake showed the same nothing, with more than 3 servings a day of caffeinated beverages giving 0.99 against none, and more than 2 servings of caffeinated coffee giving 0.93.
The authors described their findings as reassuring that caffeine exposure from usual low to moderate intake likely does not influence fecundability. Because exposure was measured biochemically, this is the strongest evidence available on the question.
The large prospective cohort, and its surprise
Hatch and colleagues[2] followed 3,628 Danish women planning a pregnancy between 2007 and 2010, recording beverage intake at baseline and every 8 weeks until pregnancy or 12 cycles. Caffeine intake of 300 mg or more a day compared with under 100 mg gave a fecundability ratio of 1.04. Three or more servings of coffee a day compared with none gave 1.05. Neither is a meaningful difference.
The interesting result was elsewhere. Soda consumption was associated with reduced fecundability, with adjusted ratios falling across intake categories to 0.48 for 3 or more servings a day, while tea drinking was associated with a slight increase, at 1.27 for 2 or more servings. The authors were careful to say that both of those could reflect unmeasured lifestyle characteristics rather than the drinks themselves.
That pattern, coffee neutral and soda unfavourable, recurs in this literature often enough to be worth noticing. It is also a strong hint that what is being measured in some studies is not caffeine at all.
What the pooled evidence says
Bu and colleagues[3] systematically reviewed controlled clinical studies, finding 4 eligible studies covering 12,912 participants. Low caffeine intake gave an odds ratio for infertility of 0.95, medium 1.14 and high 1.86, but the high-intake estimate carried an interval from 0.28 to 12.22, which is another way of saying the data could not distinguish anything. They concluded that caffeine intake at low, medium or high doses does not appear to increase infertility risk, while rating the whole body of evidence low quality and advising caution.
That is a fair summary of the female side: no signal, on evidence that is not strong enough to rule out a small one.
The male side is less clean
Male fertility gets less attention in this conversation and the evidence is more mixed. Ricci and colleagues[4] reviewed 28 observational papers covering 19,967 men. Their findings split three ways. Semen parameters did not seem affected by caffeine intake from coffee, tea and cocoa in most studies. Cola-containing beverages and caffeinated soft drinks were associated with reduced semen volume, count and concentration in some contributions. And caffeine intake appeared associated with sperm aneuploidy and DNA breaks, though not with other markers of DNA damage.
Male coffee drinking was associated with prolonged time to pregnancy in some studies but not others. Their conclusion was that caffeine may negatively affect male reproductive function, possibly through sperm DNA damage, while the epidemiological evidence on semen parameters and fertility is inconsistent and inconclusive.
Two other syntheses put that in context. Li and colleagues[5] pooled 57 cross-sectional studies covering 29,914 men across 26 countries, examining six factors including coffee consumption, and identified higher age, smoking, alcohol consumption and psychological stress as risk factors for semen quality. Coffee did not emerge alongside them. Salas-Huetos and colleagues[6] reviewed dietary patterns in male fertility and reached similar conclusions about where the strongest dietary signals lie.
Cola keeps appearing, and it is not the caffeine
Across both the female and male literature, the drink most consistently associated with worse outcomes is soft drink rather than coffee. Soda usually delivers less caffeine per serving than coffee, so if caffeine were the mechanism, coffee should look worse and it does not.
The plausible explanations are sugar, and what high soda consumption indicates about the rest of a person's diet and weight, both of which affect fertility through established routes. This does not prove soda harms fertility either, since the same confounding cuts both ways. It does mean that studies reporting caffeine effects without separating beverage types should be read carefully, because the association may belong to a different drink entirely.
Why genetics complicate the question
One reason studies disagree is that the same cup of coffee does not produce the same caffeine exposure in two people. Variation in the CYP1A2 enzyme means some people clear caffeine quickly and others slowly, as covered in our article on caffeine genetics. Cornelis and colleagues[7] showed that this genetic difference changed the relationship between coffee and heart attack risk, which is the clearest demonstration that metabolism rate can flip a coffee finding.
Almost no fertility study has accounted for it. That is precisely why measuring serum metabolites, as Purdue-Smithe and colleagues[1] did, is a step forward: blood levels capture what the body was actually exposed to, whatever the person drank and however fast they process it. The fact that the best-measured study is also the most clearly null is worth something.
What about IVF and assisted conception?
Couples going through fertility treatment often receive the strictest caffeine advice, and the research base for that is thinner than the confidence with which it is given. The studies summarised here looked at natural conception, measured as time to pregnancy or as diagnosed infertility, not at treatment cycles.
Bu and colleagues[3] noted the low quality of the whole evidence base, and a treatment setting adds its own complications: people undergoing treatment differ from the general population in age and underlying diagnosis, both of which dominate outcomes. If a clinic advises cutting caffeine during a cycle, that may be a reasonable precaution given imperfect evidence, and this article is not a reason to argue with it. It is a reason not to add guilt about coffee to an already difficult process.
What this does not cover
This article stops at conception on purpose. Caffeine during pregnancy is a distinct question with different evidence and different official guidance, covered in our article on caffeine and pregnancy, and the advice there is more conservative for good reason. Caffeine while breastfeeding is covered in our article on that.
It is also worth saying plainly that none of this research supports coffee as a fertility treatment or as a factor worth optimising. The finding is an absence, not a benefit.
What counts as high intake, in cups
The studies above describe intake in milligrams, and people drink cups, so the translation matters. McCusker and colleagues[8] measured specialty coffees and found 58 to 259 mg of caffeine per serving, with a 16-ounce brewed coffee averaging 188 mg. On those figures, the Danish cohort's high category of 300 mg or more a day is roughly two large brewed coffees, and could be one very strong one.
This is why blanket advice to cut caffeine is so hard to follow sensibly. A person drinking three small espressos and a person drinking two large brewed coffees may be told the same thing while receiving very different doses, and the studies that found nothing were covering the range most coffee drinkers live in rather than extreme intakes. Nobody has good data on what happens well above 600 mg a day while trying to conceive, because few participants drink that much.
A note on the male partner
Fertility advice is still disproportionately aimed at women, and the evidence here does not justify that split. Male factors contribute to roughly a quarter of infertility cases, as Salas-Huetos and colleagues[6] note, and the male caffeine literature is the messier of the two, with signals around sperm DNA that the female literature does not have an equivalent of.
That is not a reason for men to give up coffee, since the same reviews found semen parameters largely unaffected by coffee itself. It is a reason for the conversation to include both partners, and for the factors with stronger evidence, smoking, alcohol, weight and heat exposure, to come before coffee in either partner.
Reading this from the Philippines
Fertility care is expensive and unevenly available here, which makes the temptation to fix things through diet stronger, and dietary advice from clinics, family and the internet correspondingly harder to sort through. On the evidence above, cutting coffee is not one of the changes with support behind it. The factors that did show up repeatedly across these reviews, smoking, alcohol, body weight and age, are the ones worth attention. If sweetened iced coffee or soft drinks make up a large part of daily fluids, the sugar is the more defensible thing to reduce, on general grounds rather than on any specific fertility finding.
The limits of this evidence
Every study here is observational. Nobody has randomised people to drink coffee while trying to conceive, and nobody will. The strongest study was conducted within a trial of women with a history of one or two pregnancy losses, so it is not a general population sample. The Danish cohort relied on self-reported beverage intake. The male literature is dominated by cross-sectional studies with inconsistent semen analysis protocols, which the reviewers themselves identified as the field's central weakness. And the pooled female evidence was rated low quality by the reviewers who pooled it.
The practical answer
On the best available evidence, ordinary coffee drinking does not appear to delay conception. The study that measured caffeine in blood rather than asking about cups found no association, and the largest prospective cohort found none for coffee while finding a negative association for soda. The male evidence is less settled, with some signals around sperm DNA that deserve further work, and with cola rather than coffee carrying the clearer negative associations. If you are trying to conceive and enjoy coffee, the research does not give you a reason to give it up, though it also cannot rule out a small effect, and pregnancy itself brings different guidance. See also our article on caffeine and pregnancy and our article on safe caffeine limits. Nothing here is medical advice, and fertility questions belong with a clinician who knows your situation.