We investigated the coffee consumption pattern before pregnancy and its association with the risk of threatened abortion in Korean pregnant women. Herein, habitual coffee consumption 1 or more cup of coffee per day before pregnancy was significantly associated with an increased risk of threatened abortion during early pregnancy even after adjustment for cigarette smoking and alcohol consumption; however, the type of coffee did not significantly affect the risk of threatened abortion.
Pregnancies with the risk of threatened abortion in the first trimester occur about 15-20% of all pregnancies, however, there is still insufficient information about its risk factor and the way of prevention[16, 17]. In the present of 4,111 pregnant women, although the average maternal age of participants was relatively high, the overall prevalence of threatened abortion was 18.1%, similar to previous results. Since threatened abortion has been shown to be associated with an increased risk of poor pregnancy outcomes, approximately 50% of pregnant women who experienced threatened abortion eventually suffer miscarriages, it is required to be diagnosed and managed prevent maternal of fetal mortalities and morbidities[12, 18, 19].
Even though the market for caffeinated beverages has increased in the past decades, the most frequently consumed caffeine beverage is coffee[1, 7]. A standard cup of coffee generally expected to provide 100 mg of caffeine, however, it varies according to portion size, brewing method, and brand[1-3, 6, 7, 20]. Caffeine content in other beverages as follows: 64.0 mg in cup of tea, 46.0 mg in 12 oz of coke, 16.0 mg in cup of hot chocolate, and 46.0 mg in cup of caffeinated soda, but this caffeinated beverages do not significantly impact on daily caffeine consumption among Korean[7, 21]. Nisenblat et al reported that caffeine intake is not associated with an increased the risk of threatened abortion, with possible exception of intake of very high levels of caffeine intake [20]. However, caffeine and its metabolites easily cross the placenta and may exist in considerable quantities in the amniotic fluid and fetal blood[8, 22]. Moreover, the fetus metabolizes caffeine very slowly and even extremely small amount of maternal caffeine intake can be expected to lead to long-term fetal caffeine exposure[20, 22]. Regarding potential biological activities in experimental and human studies, caffeine exposure induces angiotensin by stimulating reactive oxygen species, which ultimately inhibit angiogenesis and negatively impact on the developing embryo[23]. In addition, caffeine consumption could increase generate of circulating catecholamines, which could cause uteroplacental vasoconstriction leading to fetal hypoxia [20, 24, 25].
Although the threshold for caffeine’s adverse effect on pregnant women was not well established, high levels of caffeine intake could have adverse effects on miscarriage, fetal growth restriction, and long-term behavioral effects in offspring[9, 11, 14, 20, 21, 26, 27].
Recently, some epidemiologic studies have found a significant association between 300 mg or more of caffeine intake per day and the risk of spontaneous abortion[21, 28, 29]. Consistent with previous studies, we have found that pregnant women with heavy coffee drinking were significantly at increased risk for having threatened abortion. In Chinese prospective study, caffeine intake before pregnancy did not increase the risk of spontaneous abortion, but caffeine intake more than 300 mg/day during the first trimester appeared to be significantly increased the risk[21]. The UK case-control study showed that caffeine consumption more than 300 mg/day during pregnancy about doubles the risk of miscarriage and its effect is driven by coffee consumption[28]. Similarly, adjusted risk among Danish women who consumed caffeine more than 375 mg/day was 2.21[29].
One meta-analysis has evaluated the risk of pregnancy loss increased by 3% for every increase in consumption of two cups of coffee per day[26]. For this reason, most women try to reduce their caffeine intake considerably during pregnancy, especially from the time when they prepare for pregnancy to first trimester[9, 27]. The current guidelines of World Health Organization recommend a caffeine intake below 300 mg/day, while the American College of Obstetricians and Gynecologists recommending a maximum caffeine intake of 200 mg/day[30, 31]. Different recommendations in guidelines can lead to confusion in preparing for pregnancy or in pregnant women. In addition, it is difficult to know the exact caffeine content because the amount varies depending on the size of coffee.
There are several limitations to this study that should be noted. The main limitation of the present study relates to inaccurate assessment of coffee consumption pattern because a ‘cup’ of coffee varies according to portion size, brewing method, and brand type. Despite the huge popularity of decaffeinated coffee in the market, we cannot measure its amount. In future studies, objective measurements including combine biomarkers of caffeine exposure in blood, urine, and saliva with 24-hour dietary recall measurement should be needed to assess quantity of precise coffee consumption. Second, typical recall bias due to retrospective assessment of caffeine consumption should be considered. However, we may reduce the impact of recall bias since we measured assessment of coffee consumption before the onset of threated abortion. Third, coffee consumption pattern before the pregnancy at only one single time point may not reflect chronic exposure over the years because women who prepare conceive tend to keep their eating habits healthy before become pregnant. Finally, although we controlled for several potential confounders in our analysis, residual confounding by diet or other lifestyle factors effects may have been present.
As the younger women continue to experience a western coffee culture and demand high quality coffee beans, this trend is expected to continue. The properties of coffee are regard as a double-edged sword and the balance between beneficial and harmful impacts on health. In this study, a high consumption of coffee to pregnancy seems to be associated with an increased risk of threatened abortion, whereas the type of coffee does not influence the risk. Among women who experienced threatened abortion during follow-up, a larger fraction was habitual coffee drinkers before the pregnancy compared with women who were seldom coffee drinkers.