August 24, 2020

expert reaction to a study looking at caffeine and pregnancy

A study, published in BMJ Evidence Based Medicin, looked at caffeine use and pregnancy.

Dr Daghni Rajasingham, Consultant Obstetrician and spokesperson for the Royal College of Obstetricians and Gynaecologists, said:

“The findings of this study add to the large body of evidence that supports limited caffeine intake during pregnancy, but pregnant women do not need to completely cut out caffeine, as this paper suggests.

“As the study notes, high levels of caffeine during pregnancy can lead to miscarriage and babies having a low birth weight and may lead to excess weight gain in the child’s early years, which can increase risk of health problems later in life. However, as other – and potentially more reliable – research has found, pregnant women do not need to cut caffeine out entirely because these 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 milligrams (mg) per day – the equivalent to two cups of instant coffee – 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 pregnancy women.”

Dr Adam Jacobs, Associate Director of Biostatistics, Premier Research, said:

“I note the author has published 2 books on the dangers of coffee which in my opinion should have been included in declarations of interest for the journal article.

“One of the factors mentioned as a strength of the paper is that the meta-analyses had consistent results. It seems likely that the meta analyses are summarising mostly the same primary studies, so that consistency is hardly surprising. If the primary studies are affected by biases and confounding, then those biases and confounding are going to be consistently brought through into the meta-analysis.

“There are some obvious potential confounders here. Given that pregnant women have been advised to avoid excessive caffeine consumption for at least the last 40 years, you might expect that women who drink coffee during pregnancy are generally less likely to follow health advice, and possibly in some ways which are quite hard to measure. Even if obvious confounders such as smoking status are taken into account, more subtle confounders may still have affected the analysis and make it hard to be sure that any observed associations with caffeine use are causal.

“There is also the question of publication bias. In general, null studies are less likely to be published than studies with positive results, so it’s possible that there have been other, unpublished, studies showing that caffeine has no effect on pregnancy outcomes. This is not addressed in the paper at all.

“Finally, I note that the paper is a narrative review, which is generally less reliable than a systematic review.

“Overall, I think if I were a pregnant woman, I don’t think this paper would make me overly concerned about drinking the occasional cup of coffee.”

Prof Andrew Shennan, Professor of Obstetrics, Kings College London, said:

“Caffeine has been in human diets for a long time, found in tea, beans and nuts. Like many substances found in a normal diet, harms in pregnancy can be found with high doses. This well conducted review confirmed the variable evidence found in the literature.

“The harmful evidence can, in part, be accounted for by other associated factors that go with high caffeine intake, such as cigarette smoking.

“It is reassuring that preterm birth was not related to caffeine intake.

“There is, however, a dose affect i.e. the more intake the higher the harm, suggesting that caffeine is the cause of the harm, rather than just associated; however this does not necessarily imply lower doses are harmful. It is well known that women may report lower intake then actual consumption in studies and could explain why lower caffeine intake looks harmful.

“The authors conclude the advice from health bodies such as the NHS needs to radically change and they advise avoiding all caffeine. However the observational nature of this data with its inherent bias does not indicate with any certainty that low doses of caffeine are harmful, and the current advice to avoid high doses of caffeine are unlikely to change.”

‘Maternal caffeine consumption and pregnancy outcomes: a narrative review with implications for advice to mothers and mothers-to-be’ by James was published in BMJ Evidence Based Medicine at 23:30 UK time on Monday 24^th August.

DOI: 10.1136/bmjebm-2020-111432

Declared interests

Dr Adam Jacobs: “I don’t have any conflicts of interests to declare.”

Prof Andrew Shennan: “I have no conflicts of interest with this subject matter.”

None others received.