Researchers looking at whether a high intake of caffeine during pregnancy is linked to low birth weights are to report back next year.
The study of 3,000 pregnant women, commissioned by the official food watchdog, will provide a basis for its advice to expectant mothers.
The findings should reduce uncertainties around the current risk assessment, the Committee on Toxicity (Cot) said.
A 2001 Cot review found links between the intake of more than 300mg of per day of caffeine, and low birth weight babies or miscarriages.
But there were some uncertainties in the available data, as research focused on intake from coffee rather than all sources of caffeine. Therefore, it was decided more research was needed.
"As a result the Agency commissioned a prospective study, involving around 3,000 pregnant women, in order to reduce uncertainties in the risk assessment and provide a robust basis for the Agency's advice to pregnant women on caffeine consumption," a Cot statement said.
The research, due to be completed early in 2008, is being carried out by scientists at Leicester and Leeds universities.
When the project was announced back in 2004, the Food Standards Agency (FSA) said: "This study is of importance as it links, for the first time, accurate estimates of caffeine intake, interindividual variations in caffeine metabolism and pregnancy outcome."