Experts could soon be able to give pregnant women precise advice about safe caffeine intake.
Caffeine intake will be monitored
Researchers at the Universities of Leicester and Leeds have been commissioned by the Food Standards Agency (FSA) to study the possible links between maternal caffeine consumption and low birth weight.
The Agency commissioned the study to reduce uncertainties in the current risk assessment, and enable them to give more robust advice to pregnant women.
In 2001 the Committee on Toxicity of Chemicals in Food, Consumer Products and the Environment (CoT) looked at the effects of caffeine on reproduction and concluded that caffeine intakes above 300mg a day may be associated with low birth weight and, in some cases, miscarriage.
Food and drink diaries
Caffeine occurs naturally in a range of foods such as coffee, tea and chocolate.
It is also added to some soft drinks and so called "energy" drinks.
A lot of people think that, given the large number of studies examining caffeine intake in pregnancy, safe limits should have been determined long ago
Dr Marcus Cooke,
300 mg of caffeine is roughly equivalent to: four average cups or three average mugs of instant coffee; three average cups of brewed coffee; six average cups of tea; eight cans of regular cola drinks; four cans of so-called "energy" drinks or 400g (eight standard 50g bars) of normal chocolate.
The university teams will look at the impact of all these sources of caffeine intake, not just tea and coffee.
And over the course of three years they will study about 3,000 pregnant women - 10% of whom are estimated to deliver babies with low birth weights.
The research will include the women being asked to keep a three-day food and drink diary.
Dr Marcus Cooke, who heads the Leicester team, said: "A lot of people think that, given the large number of studies examining caffeine intake in pregnancy, safe limits should have been determined long ago.
"However, many of these studies contain clear methodological short-comings preventing bodies, such as the FSA, giving precise advice.
"Our study is designed to overcome these limitations.
"This multi-disciplinary study brings together experts in biomonitoring, public health, epidemiology, nutrition, obstetrics and midwifery."
Roger Cook, spokesman for the British Coffee Association, said he was confident coffee was safe to drink in moderation during pregnancy.
"Coffee is one of the most heavily researched commodities in the world today, and literally thousands of scientific studies have shown that in moderation (four to five cups per day) coffee drinking is perfectly safe, and indeed, is increasingly being shown to have beneficial effects.
"The Centre for Pregnancy Nutrition here in the UK say that up to five cups of ordinary strength coffee (or 10 cups of tea) a day is a safe upper limit for pregnant women, and the Royal College of Midwives states 'there is no definitive evidence to show that caffeine in moderation has an adverse impact during pregnancy'."