Caffeine consumption during pregnancy is linked to low birth weight babies as well as an overall increase in the length of gestation, reveals new research published in the journal BMC Medicine.

While an embryo/fetus is still developing, maternal nutrition is very important, especially considering that some of the products that adults consume can be very detrimental to their health while in the womb and later on in life.

Caffeine is able to freely pass the placental barrier in the same way that nutrients or oxygen can. However, an embryo is not able to inactivate the drug properly, which can cause health concerns.

The World Health Organization (WHO) currently recommends that pregnant women consume no more than 300mg of caffeine per day - the amount contained in around two cups of medium strength coffee.

A time for a cup of coffee
A regular cup of coffee can contain anywhere between 90-200 mg of caffeine.

The effects of consuming caffeine during pregnancy

A group of researchers from the Norwegian Institute for Public Health carried out a study to try and evaluate the impact that caffeine consumption has during pregnancy.

The study included a total of 60,000 pregnancies, the researchers collected information about the mothers' diets and birth details over a 10-year period.

They also monitored how much caffeine the mothers consumed, considering a variety of different sources, such as:
  • Coffee
  • Tea
  • Soft drinks
  • Chocolate
  • Other foods containing cocoa
They found an association between caffeine consumption and the baby being small for gestational age at birth (SGA). This link was found regardless of whether the mothers smoked, indicating that it was definitely solely due to caffeine consumption.

Leader of the study, Dr Verena Sengpiel, from Sahlgrenska University Hospital, Sweden, said:

"Although caffeine consumption is strongly correlated with smoking which is known to increase the risk for both preterm delivery and the baby being small for gestational age at birth (SGA). In this study we found no association between either total caffeine or coffee caffeine and preterm delivery but we did find an association between caffeine and SGA.

This association remained even when we looked only at non-smoking mothers which implies that the caffeine itself is also having an effect on birth weight."

Caffeine from all sources reduced birth weight and increased the overall length of pregnancy. For every 100mg of caffeine consumed the birth weight went down by about 21-28 grams and the gestation period lengthened by 5 hours. Interestingly, if the caffeine came from coffee, the gestational period increased by 8 hours for every 100mg consumed - a pronounced difference.

The increased gestational length associated with coffee consumption could either have been due to another substance in coffee, or possibly there was something unique in the behaviors of the coffee drinkers - which caused increased pregnancy length - not found in those who only drank teas, the researchers wrote.

Babies who are born small for their gestational age are more likely to develop serious short- and long-term health problems. Therefore, given the findings of this study, it looks as though the recommended limit of 300mg of caffeine needs to be revised.

A previous study carried out on mice, although plausible in humans, which was published in The FASEB Journal, found that drinking the equivalent of two cups of coffee while pregnant could be enough to affect heart function of offspring throughout their lives.

Written by Joseph Nordqvist