Researchers are still unsure why this is the case, though it is thought that it could be linked more to the behaviour rather than the effects of the coffee itself. The study was held independent of smoking, which has also shown these effects during pregnancy. The current guidelines in the UK recommend that women consume no more than 300 milligrams of coffee each day, whilst Nordic countries advise no more than 200 milligrams.
If a baby has a gestational weight of 2.5kg or less, it is said to be small – some babies suffer from complications, both during birth and long term, if they are underweight, including neurodevelopment issues. Caffeine can pass along the placental barrier along with other nutrients, but is not inactivated by the foetus during development.
The study involved analysing the effects of caffeine on 59,123 pregnant women, where researchers collected information about diet and the outcome of birth. The effects were higher in those who consumed more caffeine than in those who had an intake of 50 milligrams each day. The effects remained even in non-smoking mothers, which shows that caffeine alone can have a damaging effect on the birth weight of your child. The study did not conclude why coffee effects pregnancy in this way, but it was also noted that it can also lengthen pregnancy by up to eight hours for every 100 milligram of coffee.