Women who are pregnant or who are trying to conceive should avoid caffeine because there is “no safe level of consumption”, according to an observational study published today.
The analysis, published in BMJ Evidence-Based Medicine, reviewed current evidence on caffeine-related pregnancy outcomes, to determine if the recommended safe level of consumption for pregnant women is sound.
Existing guidance, used by the NHS, the American College of Obstetricians and Gynecologists, the Dietary Guidelines for Americans and the European Food Safety Authority (EFSA), says 200mg caffeine, about two cups of moderate-strength coffee per day, is safe. This is likely now to be reconsidered, a senior midwife said.
However, Professor Jack James, of Reykjavik University, Iceland, has urged caution after completing an observational study.
After identifying 1,261 English language peer-reviewed articles linking caffeine and caffeinated beverages to pregnancy outcomes, he analysed 48 original observational studies and meta-analyses published in the past 20 years.
These reported 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 leukaemia, and childhood overweight and obesity.
There were 42 separate findings reported in 37 observational studies and of these, 32 found that caffeine significantly increased risk of adverse pregnancy outcomes, while 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.
Eleven studies reported on the findings of 17 meta-analyses, of which 14 associated maternal caffeine consumption with increased risk for four adverse outcomes: miscarriage, stillbirth, low birth weight and/or small for gestational age, and childhood acute leukaemia.
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 maternal caffeine consumption and childhood overweight and obesity, but four out of five observational studies reported significant associations.
Although Prof James admits the results could be affected by other confounding factors, such as recall of caffeine consumption, maternal cigarette smoking and pregnancy symptoms, he says the dose-responsive nature of the associations between caffeine and adverse pregnancy outcomes, as well as the fact that some studies found no threshold below which negative outcomes were absent, supports likely causation rather than association.
He says 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 leukaemia and childhood overweight and obesity, but not preterm birth.
Dr Mary Ross-Davie, who is Scottish director of the Royal College of Midwives, said: “Current NHS guidance on caffeine in pregnancy says that women should limit their intake to no more than 200mg of caffeine a day, equivalent to around two cups of instant coffee. There is a need to ensure that women are able to make informed choices about what they eat and drink during pregnancy, and midwives will support women to do that, taking into account this latest research.
“It is important that all available evidence is considered to shape UK recommendations, and we hope the current guidance will now be reviewed in light of these findings.”
James JE. Maternal caffeine consumption and pregnancy outcomes: a narrative review with implications for advice to mothers and mothers-to-be. BMJ Evidence-Based Medicine 25 August 2020; doi. 10.1136/bmjebm-2020-111432
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