According to the National Health Service, consuming 200mg or less of caffeine a day should not pose any significant risk in terms of miscarriage or growth of the baby while in the womb. Likewise, the European Food Safety Authority and the American and UK Colleges of Obstetricians and Gynaecologists recommend limiting, but not entirely eliminating, caffeine consumption during pregnancy.

However, Professor Jack E. James at Reykjavik University in Iceland said no amount of caffeine consumption is safe during pregnancy. James conducted a narrative review of studies to assess current evidence on pregnancy outcomes related to caffeine intake – many guidelines for caffeine consumption in pregnant women call for reduced intake, as it contributes to negative pregnancy outcomes such as low birth weight, preterm birth, and childhood overweight and obesity.

James also acknowledges that the work is observational, and so can’t prove definitively that any caffeine in pregnancy is harmful.

Other experts strongly disagree, including Obstetrics Professor Andrew Shennan at Kings College London. He said that some of the studies in the analysis may be flawed because they rely on women recalling caffeine intake. Additionally, it would be difficult to exclude other risk factors that tea or coffee drinkers might be indulging in, such as cigarette smoking.

“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 is unlikely to change.”

Echoing the disagreement, Dr. Luke Grzeskowiak, a pharmacist at the University of Adelaide, Australia, said the recent research was inconsistent with accepted evidence and “overly alarmist.”

“There are so many dos and don’ts associated with pregnancy and the last thing we need is to cause unnecessary anxiety. At the end of the day, women should be reassured that caffeine can be consumed in moderation during pregnancy,” Dr. Grzeskowiak said.