Women who are pregnant or trying for a baby should consider avoiding caffeine altogether, new research has suggested.
Current guidance suggests pregnant women should limit the amount of caffeine they consume to 200 milligrams a day.
However, a new study concludes that pregnant women, or those trying for a baby, should avoid caffeine completely.
Caffeine is found naturally in some foods and drinks, such as tea, coffee and chocolate. It is also added to some energy drinks, cold and flu remedies and some soft drinks.
The new study, published in the journal BMJ Evidence Based Medicine, examined data from 37 observational studies.
The research, by Professor Jack James, of Reykjavik University in Iceland, found that 32 of these studies reported that caffeine significantly increased risk of adverse pregnancy outcomes including stillbirth, miscarriage and low birth weight.
He also cited an increased risk of childhood acute leukaemia and children being overweight or obese when born to mothers who consume caffeine during pregnancy.
Prof James wrote: "Current advice such as that issued by ... the [UK] NHS is not consistent with the level of threat indicated by biological plausibility of harm and extensive empirical evidence of actual harm.
"Accordingly, current health recommendations concerning caffeine consumption during pregnancy are in need of radical revision.
"Specifically, the cumulative scientific evidence supports pregnant women and women contemplating pregnancy being advised to avoid caffeine."
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 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."
Commenting on the study, Dr Mary Ross-Davie, director for Scotland at 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."