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.

Share your comments below


  • I drank tea and I had really big babies. Everyone is different.


  • I don’t drink coffee. I used to drink some tea while pregnant (now just herbal teas) but no more than twice a day.


  • I didn’t have much coffee throughout my pregnancy, a tea now and then.


  • I’m glad I’ve had my children. Being pregnant these days is so stressful with all there studies telling you what you shouldn’t have !


  • Not really sure about this study, I think they need to test further. I drank 2 cups of coffee a day when I was pregnant and did not have any issues with my baby, and even drank coffee while breastfeeding (usually after I finished the feeding though). But I did not drink instant coffee, I drank filtered black with no sugar or milk. If you keep your liver healthy by not drinking alcohol, then it might not be a problem, eating healthy is more important with lots of fresh veg and fruit.


  • I switched to decaf coffee for my first two pregnancies as I found I was going to the toilet like I was in my 3rd trimester with the caffeine! My third I couldn’t drink any hot drinks (or eat anything) until after noon I was so sick for the first 20 weeks, and even once the morning sickness was gone I couldn’t drink coffee.
    My babies were all in the 6lb range, caffeine didn’t contribute to their weights!


  • Couldn’t stand the smell of coffee or tea when I was pregnant along with many other smells. Guess that’s why I had three normal healthy babies – 4th one was problematical due to my having to have a Rubella injection when I was 3 months pregnant.


  • I cut my caffeine intake but still had 1 or 2 drinks (tea or coffee) a day as everyone told me this amount was fine. Bub weighed a healthy 3.5kg and 5 days early.


  • I drank coffe but always weak coffee
    I had gestational diabetes with both my pregnancies fist pregnancy I have it up and the 2nd pregnancy I drank weak coffee it helped with sugar count


  • I usually love coffee, but when I was pregnant, I couldn’t stomach it at all. Even the smell made me feel sick…not good when you work part time as a barista lol


  • I couldn’t stomach coffee with my pregnancy but drank tea. I didn’t think tea had much caffeine in it? And also what about things like chocolate?


  • I drank coffee and tea in my first pregnancy but couldn’t stand it in my second or third. And guess what all three babies are all around the same weight when they were born.
    So this “research” didnt work for me.


  • I sure drank coffee and tea during my pregnancies, but always drink decaf coffee and herbal caffeine free tea. Black tea is very much consumed in the UK and Ireland indeed.


  • We often forget about tea having caffeine. Great reminder for me


  • If this was the case my 2nd niece would have been really tiny. By normal standards she was a big baby. However she was a restless baby.


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