Caffeine, Fertility and Pregnancy

While the evidence is limited and sometimes conflicting, some studies suggest that high consumption of caffeine during pregnancy may be associated with an increased risk of adverse pregnancy outcomes, including miscarriage.

Background

Because caffeine crosses the placenta and enters the baby's bloodstream, and the developing fetus lacks the enzymes required to break down caffeine, the stimulant stays in their system for a much longer period than it does in the mother's, carrying a substantial risk for their development and survival. In addition, caffeine may also affect fertility before pregnancy begins. Experimental studies suggest that caffeine can delay the transport of the embryo through the fallopian tube. As a result, the embryo may reach the uterus after the optimal window of implantation has begun to close, potentially reducing the likelihood of successful implantation.

Introduction

Although caffeine consumption in adults has beneficial effects on neurological diseases cardiovascular diseases, certain cancers, liver diseases and type 2 diabetes, it has also been well documented that maternal caffeine consumption during pregnancy increases the risk of pregnancy failure or gestational complications. For example, a meta-analysis published in 2015 by Public Health Nutrition concluded that:

“Higher maternal caffeine intake was associated with a higher risk of pregnancy loss and adherence to guidelines to avoid high caffeine intake during pregnancy appears prudent.”

Fertility may also be impacted by caffeine. A 2019 review published in Trends in Endocrinology & Metabolism proposed that caffeine may impair fertility by delaying embryo transport through the fallopian tube. This delay could cause the embryo to miss the optimal window for implantation, thereby reducing the chances of a successful pregnancy.

Sources of Caffeine

Caffeine is found in many beverages and foods, not just coffee. Black, green, white, and oolong teas all contain caffeine, although typically in lower amounts than coffee. However, caffeine has the same biological effects regardless of its source. Energy drinks, cola beverages, dark chocolate, and certain medications may also contribute significantly to a person's total daily caffeine intake. Therefore, women who are pregnant or trying to conceive should consider their cumulative caffeine consumption rather than focusing solely on coffee. Regardless of whether caffeine comes from coffee, tea, energy drinks, or chocolate, it readily crosses the placenta and is metabolized very slowly by the developing fetus.

Unlike black or green tea, most herbal teas are naturally caffeine-free. However, being caffeine-free does not necessarily mean they are safe during pregnancy. Herbal teas contain biologically active compounds that may influence uterine activity, hormone signaling, or fetal development. Because many herbal products have not been adequately studied in pregnant women, several professional organizations recommend caution, particularly during the first trimester. Herbs such as pennyroyal should be avoided because of known toxicity, while others—including chamomile, hibiscus, parsley, and certain medicinal herbal blends—should be consumed only with caution due to limited safety data.

What's Too Much Caffeine

Major health organizations, including the American College of Obstetricians and Gynecologists (ACOG), recommend that pregnant women limit their total caffeine intake to less than 200 milligrams (mg) per day. For perspective, an average 8-ounce cup of black tea contains approximately 40–50 mg of caffeine, while an 8-ounce cup of brewed coffee typically contains 80–120 mg. Because many coffee shops serve larger portions, a 12-ounce ("Tall" or "Small") brewed coffee may contain approximately 140–180 mg of caffeine, while a 16-ounce ("Grande") may provide 200 mg or more. Again, when estimating daily caffeine intake, it is important to consider all sources of caffeine—including coffee, tea, energy drinks, soft drinks, chocolate, and certain medications—not just coffee.

Half-Life of Caffeine

Half-life is the amount of time it takes for the body to eliminate half of a substance. For most healthy adults, the half-life of caffeine ranges from about 5 to 10 hours, although it can vary depending on factors such as age, genetics, liver function, medications, and pregnancy.

For example, assume a half-life of 10 hours. If a person drinks a 12-ounce cup of coffee containing approximately 140 mg of caffeine, about 70 mg will remain in the body 10 hours later. After another 10 hours, about 35 mg will remain, and after 30 hours, approximately 17 mg will still be present. In other words, caffeine does not disappear all at once—it is gradually eliminated over time. If that person drinks another cup of coffee the following morning, some caffeine from the previous day's cup is still present, adding to the caffeine from the new cup.

During pregnancy, caffeine is cleared much more slowly. By the third trimester, its half-life can increase to 10–18 hours or even longer, meaning both the mother and the fetus are exposed to caffeine for a prolonged period.

Acupuncture and Caffeine

The effects of caffeine can also be seeing in acupuncture. One of the biological mechanisms by which acupuncture exerts its effects involves the release of adenosine, a naturally occurring molecule that promotes relaxation and helps modulate pain. Because caffeine acts as an adenosine receptor antagonist, it may reduce some of the biological effects mediated by adenosine, potentially diminishing certain effects of acupuncture.

A randomized controlled trial published in Frontiers in Neurology in 2022 investigated whether caffeine consumption influences the effects of electroacupuncture. After four weeks, the researchers concluded that "moderate caffeine intake reduced the effects of electroacupuncture," suggesting that caffeine may interfere with some of acupuncture's therapeutic mechanisms.

Although acupuncture has been shown to reduce sympathetic nervous system activity, lower stress hormone levels, and alleviate anxiety, no clinical trials have specifically evaluated its ability to counteract caffeine-induced overstimulation. Nevertheless, acupuncture's well-documented effects on autonomic regulation provide a biologically plausible mechanism by which it may help patients experiencing caffeine-related anxiety or sympathetic overactivation.

This interaction between caffeine and acupuncture may be particularly relevant for patients undergoing fertility treatment or during pregnancy, where both minimizing excessive caffeine intake and promoting parasympathetic activity are often considered important components of supportive care.

Conclusion

While trying to conceive, experimental studies suggest that caffeine may delay embryo transport through the fallopian tube, potentially causing the embryo to miss the optimal window for implantation. During pregnancy, higher caffeine intake has been associated with adverse pregnancy outcomes, including an increased risk of miscarriage and low birth weight. To minimize these risks, both the American College of Obstetricians and Gynecologists (ACOG) and the World Health Organization (WHO) recommend limiting caffeine intake during pregnancy, with ACOG recommending less than 200 mg per day. Finally, to maximize the potential benefits of acupuncture, patients may wish to avoid caffeine for at least 2–4 hours before treatment, as caffeine has been shown to reduce some of the physiological effects of acupuncture. Although additional research is needed in several areas, the available evidence supports a cautious approach to caffeine consumption during the preconception period and throughout pregnancy.