Women who are trying to conceive or are pregnant should cut out caffeine entirely to minimise the risk of losing their baby, scientists have warned.
Research on more than 1,200 women suggested even low levels of caffeine pose a danger both before and during pregnancy.
The advice flies in the face of NHS guidelines, which say around two cups of instant coffee a day are safe but any more could lead to a low birth weight.
The topic is highly debated because there is evidence caffeine – which is also in tea and energy drinks – has no effect on babies in the womb.
Women who are trying to conceive or are pregnant should cut out caffeine entirely to minimise the risk of losing their baby, scientists have warned
The study, led by the US National Institutes of Health, has not been published and will be presented at the American Society for Reproductive Medicine’s (ASRM) congress in Philadelphia.
The researchers claim: ‘Any level of caffeine intake during pregnancy may increase risk of pregnancy loss, particularly in the first eight weeks’ gestation.
‘Women attempting to conceive may benefit from eliminating caffeine intake during pre-conception and early pregnancy.’
The team, led by Dr Alexandra Purdue-Smithe, went back to a 2014 study that looked at the effects of aspirin during pregnancy.
Participants – 1,228 women who attempted to get pregnant between 2007 and 2011 – were asked to report how much caffeine and alcohol they drank.
Levels of caffeine in the blood were also measured, but it is not clear if they were asked to record their diet, as foods such as chocolate contain caffeine.
The results suggested intake of two or more caffeinated drinks per day – including coffee, tea or soda – before conception was linked to a risk of pregnancy loss.
Therefore, the researchers concluded women considering pregnancy could benefit from completely removing caffeine from their diet.
Results also showed women who consumed less caffeine than the minimum recommended daily amount were still at increased risk.
The abstract said: ‘Adjustment for nausea and vomiting and other factors that change during early pregnancy showed caffeinated beverage intake at levels lower than those corresponding to medical recommendation was positively associated with risk of loss.’
The researchers did not explain why the link exists, however the effects of caffeine on the body are well understood.
Caffeine is a stimulant and can increase blood pressure and heart rate, both of which are not recommended during pregnancy.
NHS guidelines recommend pregnant women don’t drink more than 200mg of caffeine per day – about two cups of instant coffee and one cup of filtered coffee.
Too much caffeine could cause a low birth weight which can lead to health problems later in life. It could also cause a miscarriage, the NHS states.
Hugh Taylor, vice-president of the ASRM, said: ‘The data on caffeine intake and pregnancy remains somewhat inconclusive.
‘However, it is hard to see any harm that could come to women or babies from reducing or eliminating caffeine.’
Ying Cheong, professor of reproductive medicine at University of Southampton, said there was limitations to the study.
She said: ‘The study wasn’t designed to look at caffeine. The caffeine intake was self reported on questionnaires.
‘I don’t think that advice is warranted based on this abstract, which has not yet been published or peer-reviewed.
‘The ingrained coffee culture in today’s society would need many more robust studies to change.’
The study adds to a significant body of controversial literature around caffeine.
In 2008, two studies on the effects of caffeine related to miscarriage showed contrasting outcomes.
Experts at the Kaiser Permanente Division of Research found women who consumed 200mg or more of caffeine daily were twice as likely to have a miscarriage as those who do not consume any caffeine, according to the paper in the American Journal of Obstetrics and Gynecology.
The other, by Nationwide Children’s Hospital and released by Epidemiology, said there was no increased risk in women who drank a minimal amount of coffee daily – between 200-350mg per day.
Geeta Nargund, medical director of Create Fertility Clinics and an NHS consultant, told The Times: ‘This is the first study I’ve seen giving such stringent advice. It is an interesting and good study, but we do need further studies.’