Caffeine is unsafe for pregnant women and may increase risk for miscarriage and stillbirth, warns study
How safe is drinking coffee for pregnant women? According to a new study, there is no safe level of caffeine consumption for pregnant women and would-be mothers. Women who are pregnant or trying for a baby should be advised to avoid caffeine because the evidence suggests that maternal caffeine consumption is associated with negative pregnancy outcomes, cautions Dr Jack James, a professor at Reykjavik University, Iceland, who conducted the analysis.
Pregnant women have been advised that consuming a small amount of caffeine daily will not harm their baby. The NHS, the American College of Obstetricians and Gynecologists (ACOG), the Dietary Guidelines for Americans, and the European Food Safety Authority (EFSA) have set this level at about 200 milligrams (mg) caffeine, the equivalent of roughly two cups of instant coffee. However, according to the author of the current study, there is “substantial cumulative evidence” of an association between maternal caffeine consumption and diverse negative pregnancy outcomes, specifically miscarriage, stillbirth, low birth weight and/or small for gestational age, childhood acute leukemia and childhood overweight and obesity, but not preterm birth.
“The majority of relevant peer-reviewed studies report that maternal caffeine consumption is associated with an increased risk of negative pregnancy outcomes. It is generally accepted that chronic exposure to chemicals during pregnancy is cause for concern. When the chemical of interest is caffeine, a near universally consumed habit-forming substance of no nutritional value, the need for caution is compelling,” Professor James told MEA WorldWide (MEAWW).
What did the study find?
The paper is a review of current evidence on caffeine-related pregnancy outcomes, to determine whether the recommended safe level of consumption for pregnant women is soundly based. Through database searches, 1,261 peer-reviewed articles linking caffeine and caffeinated beverages to pregnancy outcomes were identified. They were narrowed down to 48 original observational studies and meta-analyses published in the past two decades reporting results for one or more of six major negative pregnancy outcomes: miscarriage, stillbirth, low birth weight and/or small for gestational age, preterm birth, childhood acute leukemia, and childhood overweight and obesity.
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A total of 42 separate findings were reported in 37 observational studies. Of these, 32 found that caffeine significantly increased the risk of adverse pregnancy outcomes, and 10 found no or inconclusive associations. Caffeine-related risk was reported with moderate to high levels of consistency for all pregnancy outcomes except preterm birth.
According to the analysis, 11 studies reported on the findings of 17 meta-analyses and in 14 of these, maternal caffeine consumption was associated with increased risk for four adverse outcomes: miscarriage, stillbirth, low birth weight, and/or small for gestational age, and childhood acute leukemia. Eight out of nine studies reported “significant associations” between caffeine and increased risk of miscarriage (loss before 20 weeks). Findings for stillbirth (loss after 20 weeks of pregnancy) were also largely consistent, with four of five observational studies reporting caffeine-related increased risk. The three remaining meta-analyses did not find an association between maternal caffeine consumption and preterm birth. No meta-analyses looked at the association between caffeine consumption during pregnancy and childhood overweight and obesity, but four of five observational studies reported significant associations.
Based on the findings, the researcher recommends that current health recommendations concerning caffeine consumption during pregnancy need “radical revision.” “Current evidence does not support assumptions about safe levels of maternal caffeine consumption. The cumulative scientific evidence supports advice to pregnant women and women contemplating pregnancy to avoid caffeine,” writes Professor James in the study published in BMJ Evidence Based Medicine.
Since this is an observational study, it cannot establish causation and the author points out that the results could be impacted by other confounding factors, such as the recall of caffeine consumption, maternal cigarette smoking and most importantly pregnancy symptoms. Pregnancy symptoms such as nausea and vomiting in early pregnancy are predictive of a healthy pregnancy and women who experience them are likely to reduce their caffeine intake. However, he adds that the dose-responsive nature of the associations between caffeine and adverse pregnancy outcomes (implying that larger amounts pose a greater risk than smaller amounts), and the fact some studies found no threshold below which negative outcomes were absent, supports likely causation rather than mere association.
The ACOG says that moderate caffeine consumption (less than 200 mg per day) does not appear to be a major contributing factor in miscarriage or preterm birth. “The relationship of caffeine to growth restriction remains undetermined. A final conclusion cannot be made at this time as to whether there is a correlation between high caffeine intake and miscarriage,” it adds.
What are experts saying?
Some experts, who were not involved in the review, have raised questions regarding the conclusions of the review. Commenting on the study, Professor Michael Davies, a reproductive epidemiologist from the Robinson Research Institute at the University of Adelaide, argues the statement that there is “no lower threshold” is not the same as no evidence of harm. “There is no clear evidence of harm at low levels of tea and coffee consumption as there is no reliable data, due to low observed risks. Maternal genes that control the metabolism of caffeine should be associated with adverse outcomes as they alter maternal and fetal exposure, but they are not. This implies a different unmeasured factor is involved,” says Davies. He, however, warns that extreme levels of exposure to, or consumption of, any substance may well adversely alter fetal development.
Dr Daghni Rajasingham, consultant obstetrician and spokesperson for the Royal College of Obstetricians and Gynaecologists, says that the findings add to the large body of evidence that supports limited caffeine intake during pregnancy, but adds that pregnant women do not need to completely cut out caffeine, as the paper suggests, because the risks are extremely small, even if the recommended caffeine limits are exceeded. “The Royal College of Obstetricians and Gynaecologists’ advise to limit caffeine intake to 200 mg per day still stands. This paper does not supersede all the other evidence that has found that a limited intake of caffeine is safe for the majority of pregnant women,” she writes.
According to Dr Alex Polyakov, a senior lecturer in the Department of Obstetrics and Gynaecology at the University of Melbourne, there is a weak association between caffeine consumption and some adverse pregnancy outcomes. “The clinical significance of this association is unclear and indeed the causative link between the two has not been established. Nevertheless, the preponderance of evidence points towards caffeine consumption being a risk factor for miscarriage, low birth weight, and to a lesser extent stillbirth and childhood leukemia. The magnitude of this risk remains unclear, but is likely to be small and of questionable clinical significance,” explains Polyakov.
Gino Pecoraro, president of the National Association of Specialist Obstetricians and Gynaecologists (NASOG) and a federal member of the Australian Medical Association (AMA) Board, says that consumption of caffeine by pregnant women is exceptionally common with over 80% of American women reporting daily caffeine use and over 90% in some European centers. “Therefore, any study looking at adverse effects associated with the consumption of caffeine during pregnancy is important and any potential new recommendations will affect a large number of women. The significant limitations in the design of the paper mean that while it is worthwhile discussing caffeine consumption with pregnant women, I’m not convinced that a total ban is warranted at this time,” emphasizes Pecoraro, an associate professor of obstetrics and gynecology at the University of Queensland.