Drinking just one cup of coffee a day during pregnancy could put a child on the path to obesity, say scientists.

It increased infants' risk of growing up overweight by 15 percent - doubling to 30 percent for those exposed to two daily cups in the womb.

And babies whose mothers regularly consumed more than three while expecting were 66 percent more vulnerable to piling on the pounds.

Children exposed to these "very high levels" of caffeine before birth weighed on average over a pound more by the time they were eight.

The Norwegian team say the findings add to concerns about caffeine during pregnancy and suggest "complete avoidance" could be the safest option.

Dr Eleni Papadopoulou, of the Norwegian Institute of Public Health in Oslo, said: "Maternal caffeine intake may modify the overall weight growth trajectory of the child from birth to eight years.

"The results add supporting evidence for the current advice to reduce caffeine intake during pregnancy and indicate that complete avoidance might actually be advisable."

The NHS recommends women should drink no more than two cups during pregnancy. But Dr Papadopoulou said less than this made children more prone to obesity.

Previous research has found a link between coffee in pregnancy and low birth weight which can lead to health problems later in life. Too much caffeine can also cause a miscarriage.

Lead author Dr Papadopoulou and colleagues said this prompted them to consider if mothers-to-be should cut out the world's most popular beverage altogether.

She said: "During pregnancy, elimination of caffeine is prolonged and it rapidly passes all biological membranes, including the blood-brain and placenta barriers, resulting in exposure of the foetus.

"A maximum intake level of caffeine for pregnant women has been stipulated by several authorities, most of which agree it should not exceed 200 mg/day, based on the evidence of its adverse effects on miscarriage rates and foetal growth restriction."

Dr Papadopoulou said earlier studies had linked caffeine to childhood obesity but this was by far the biggest and most thorough of its kind. A regular cup of coffee contains 100 mg of caffeine.

She said the study backs general advice for women to limit consumption when they are having a baby.

Caffeine stimulates the central nervous system as it passes rapidly through tissues. These include the placenta - meaning it takes longer to get rid of during pregnancy.

The researchers used data on almost 51,000 mother and infant pairs from a Norwegian health study between 2002 and 2008 and identified a link between caffeine during pregnancy and excess weight gain in children.

They were split into four groups depending on intake including 'low' (0-49 mg), 'average' (50-199 mg), 'high' ( 200-299 mg) and 'very high' (300 + mg) intake.

Exposure to any caffeine level while in the womb was associated with a heightened risk of overweight at the ages of three and five years.

This persisted for eight year olds whose mothers had a very high caffeine consumption in pregnancy - more than three cups.

These children weighed 67-83 g (2.4 to 3 oz) more when they were three to 12 months, 110-136 g (3.9 to 4.8 oz) as toddlers, 213 320 g (7.5 to 11.3 oz) as three to five year olds and 480 g (1lb 1 oz) at eight than those exposed to low levels.

Dr Papadopoulou said: "Any caffeine consumption during pregnancy is associated with a higher risk of excess infant growth and of childhood overweight, mainly at preschool ages.

"Maternal caffeine intake may modify the overall weight growth trajectory of the child from birth to eight years.

"This study adds supporting evidence for the current advice to reduce caffeine intake during pregnancy."

She said animal studies have shown caffeine programmes the offspring towards obesity and cardiometabolic disorders through alterating chemicals that play a key role in growth and metabolism.

It also effects the transportation of leptin through the placenta - a hormone that regulates appetite.

The researchers are confident in their results because of the large sample size, the consistency of the findings and a plausible biological explanation - foetal programming.

Dr Papadopoulou said: "Although most pregnant women reduce their caffeine intake during pregnancy and few have caffeine intakes higher than 200 mg/day our results show associations between caffeine intakes below 200 mg/day and excess growth."

In the study the participants were asked to quantify their food and drink intake 22 weeks into their term from among 255 items using a specially adapted Food Frequency Questionnaire.

Sources of caffeine included coffee, black tea, fizzy drinks, chocolate, chocolate milk, sandwich spreads, desserts, cakes and sweets.

Filter coffee contains more caffeine (140mg a cup). Tea has 75mg, a can of cola 40mg and one 250ml can of energy drink up to 80mg. Llarger cans may contain up to 160 mg.

The children's weight, height, and body length were subsequently measured at 11 time points between 6 weeks old and eight years.

Excess weight gain was assessed using World Health Organisation criteria, while overweight and obesity were assessed according to International Obesity Task Force criteria.

Just under half of the mums-to-be (46%) were classified as low caffeine intake; 44 percent as average intake; 7 percent as high; and 3 percent as very high.

Dr Papadopoulou said the findings held after other potentially influential factors were taken into account.

The higher the caffeine intake the greater the likelihood the mother was older than 30, had had more than one child, consumed more daily calories and smoked during her pregnancy.

And women with a very high caffeine intake during their pregnancy were more likely to be poorly educated, and to have been obese before they got pregnant.