Women have been warned for every additional 100mg of caffeine a day – around half a cup of coffee – during the first trimester, birth weight can be lowered by up 2.5 ounces.
A new study from the University College Dublin says even women who drink less than the “safe” cut-off amount of two mugs of instant coffee (or three cups of tea) a day are more at risk of having low-birth weight or premature newborns.
The reason researchers give is the caffeine as it restricts blood flow to the placenta, slowing a baby’s growth, reports The Mirror.
In the study, Dr Ling-Wei Chen looked at 941 Irish mothers and babies where tea was the mothers’ main source of caffeine (48%), followed by coffee (38%).
The results suggest that for every additional 100mg of caffeine a day – around half a cup of coffee – during the first trimester, the baby tended to have a 2.5oz lower birth weight.
This amount of caffeine also decreased the babies’ length and head circumference, as well as their gestational age, which measures the length of pregnancy.
The women who consumed the most caffeine had babies weighing around 0.37lb (170g) less than those who had the least.
Even women who drank less than the “safe” amount of caffeine saw significant effects.
Dr Chen said: “Based on the consistent associations we observed we would recommend women who are pregnant or seeking to become pregnant at least limit their intakes of caffeinated coffee and tea.
“High caffeine intake can result in restricted blood flow in the placenta which may subsequently affect foetal growth. Caffeine can also cross the placenta readily, and because caffeine clearance slows as pregnancy progresses, caffeine accumulation may occur in foetal tissues.”
The researchers are concerned that people don’t know how much caffeine is in their cuppa.
Tea has less caffeine than a cup of coffee, but the exact amount depends on the brew time, water temperature and type of tea. So a cup of black tea contains anywhere between 23mg and 110mg of caffeine.
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