Drinking tea and coffee while pregnant may be bad for the unborn baby, according to new research.

A study from University College Dublin (UCD) showed a consistent link between both caffeinated tea and coffee and negative birth outcomes.

It examined data from 941 pregnant Irish women.

The aim of the study was to examine the association between maternal caffeine intake and birth outcomes, in a population with tea as the predominant caffeine source.

However the study found that the influence of tea caffeine remained unclear.

It found caffeine intake was derived from coffee, tea, soft drinks and cocoa-containing foods and beverages.

Associations of maternal caffeine intake were investigated using multiple linear and logistic regressions.

Tea was the predominant caffeine source for 48% of women in the study.

This was followed by coffee, at 39%.

In the fully adjusted model, maternal caffeine intake was associated with lower birth weight, shorter birth length, smaller head circumference and shorter gestational age.

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Higher risks for low birth weight and preterm birth were also seen.

It said: "The associations were robust to the exclusion of participants with pregnancy complications and in never smokers.

"Similar higher risks of adverse birth outcomes were observed for the highest caffeine intake categories from coffee and tea, compared with the lowest intake categories".

In its conclusion, the study found: "Maternal caffeine intake from both coffee and tea is associated with adverse birth outcomes."

The study has been published in The American Journal of Clinical Nutrition.

The Food Safety Authority of Ireland (FSAI) has said caffeine can be absorbed freely across the placenta, but cannot be broken down by either the placenta or the foetus.

Therefore, the amount of caffeine the foetus is exposed to is very close to the amount consumed by the mother.

The guideline for the upper limit of caffeine intake in pregnancy is 200mg per day.