How drinking even half a coffee while pregnant could harm your baby

It might be advisable to avoid caffeine all together when you’re expecting, according to a spate of recent studies - meaning that even moderate coffee intake or a simple bar of chocolate could soon be off the menu for mums-to-be.

Two new studies published in February and March this year highlight the potentially harmful impact of caffeine consumption in pregnancy. The first, conducted by the University of Rochester Medical Center, found that caffeine consumed during pregnancy can change important brain pathways that could lead to behavioural problems such as ADHD later in life.

The second study, by the National Institute of Child Health and Human Development and published in JAMA Open Network on 25 March 2021, found that women who drank as little as half a cup of coffee per day on average gave birth to smaller babies than pregnant women who did not consume caffeinated beverages.

These add to the controversial but growing body of evidence that suggests that – contrary to official guidance across the world - pregnant women should cut out coffee and caffeine-containing food and beverages all together.

Official current advice on caffeine in pregnancy

Resources such as the World Health Organisation (WHO), American Pregnancy Association and the UK’s National Health Service (NHS) currently advise limiting caffeine intake to under 200mg daily during pregnancy (around one to two cups of coffee a day).

It is well known that consuming high levels of caffeine in pregnancy is linked to problems such as growth restriction, reduced birth weight, preterm birth or stillbirth. The WHO recommends that any pregnant women with a caffeine intake of more than 300mg per day lowers her intake in order to reduce these risks.

However, increasing numbers of scientists believe that there is actually no safe limit of caffeine consumption for pregnant women.

They say that although the bulk of research has focused only on high caffeine consumers, new research is revealing that even moderate and low level caffeine consumers in pregnancy may be putting their baby at risk.

What the controversial new evidence says

The latest study by National Institute of Child Health and Human Development, published on 25 March 2021 in JAMA Open Network, analyzed data on more than 2,000 racially and ethnically diverse women at 12 clinical sites who were enrolled from 8 to 13 weeks of pregnancy. The women were non-smokers and did not have any health problems before pregnancy.

Based on the women's own estimates of the beverages they drank, women who consumed about 50 milligrams of caffeine a day (equivalent to a half cup of coffee) had infants 66 grams (about 2.3 ounces) lighter than infants born to non-caffeine consumers

Meanwhile researchers in the Del Monte Institute for Neuroscience at the University of Rochester Medical Center (URMC) analyzed thousands of brain scans of nine and ten-year-olds, and revealed changes in the brain structure in children who were exposed to caffeine in utero. Elevated behavioural issues, attention difficulties, and hyperactivity are all symptoms that researchers observed in these children, according to the February 2021 study.

An analysis of more than 1,200 studies of caffeine’s effect on pregnancy and found “persuasive confirmation of increased risk … for at least five major negative pregnancy outcomes: miscarriage, stillbirth, lower birth weight and/or small for gestational age, childhood acute leukaemia, and childhood overweight and obesity.”

- Professor Jack E. James, Psychology, Reykjavik University

In addition to these two 2021 studies, a peer-reviewed study published in the journal BMJ Evidence-Based Medicine in August 2020 analysed more than 1,200 studies of caffeine’s effect on pregnancy and found “persuasive confirmation of increased risk … for at least five major negative pregnancy outcomes: miscarriage, stillbirth, lower birth weight and/or small for gestational age, childhood acute leukaemia, and childhood overweight and obesity.”

Prof Jack James, of Reykjavik University, told The Guardian that “current advice … is not consistent with the level of threat indicated by biological plausibility of harm and extensive empirical evidence of actual harm.” It concluded that health recommendations needed “radical revision”.

“The cumulative scientific evidence supports pregnant women and women contemplating pregnancy being advised to avoid caffeine,” the report said.

How is caffeine consumption different in pregnancy?

Caffeine – a central nervous system stimulant - passes rapidly through the body, including the placenta, and takes longer to process during pregnancy. This means that caffeine lingers in a pregnant woman’s bloodstream for a while after drinking coffee or other caffeine-containing substances – something called ‘caffeine clearance’. The speed of caffeine clearance varies between people, with some people metabolising caffeine much more quickly than others.

The placenta provides a growing baby with food and oxygen through the umbilical cord. Because caffeine is able to pass freely through the placenta, when a pregnant woman drinks coffee or other caffeinated beverages, the baby will also receive it.

It has been established that neither the fetus nor the placenta contains the enzyme necessary to process caffeine properly. Previous studies have linked the impact of caffeine consumption on the fetus with the pregnant mother’s ‘caffeine clearance’ rate, which depends on the individual woman.

In their report, researchers at the National Institute of Child Health and Human Development speculated that caffeine could reduce the blood supply to the fetus and inhibit growth. Similarly, researchers believe caffeine could potentially disrupt fetal stress hormones, putting infants at risk for rapid weight gain after birth and for later life obesity, heart disease and diabetes, but this is still speculation at this stage.

Does this mean I have to cut out caffeine in pregnancy completely?

The research on the impact of caffeine in pregnancy is mixed and controversial. The official public health guidance is still that pregnant women can safely consume up to 200mg of caffeine per day – which equates to 1-2 cups of coffee per day.

While many scientists are convinced by the growing evidence against caffeine consumption in pregnancy, many others are skeptical.

In a reaction piece to the 2020 study review, Dr Daghni Rajasingham, Consultant Obstetrician and spokesperson for the Royal College of Obstetricians and Gynaecologists, said: “The findings of this study add to the large body of evidence that supports limited caffeine intake during pregnancy, but pregnant women do not need to completely cut out caffeine, as this paper suggests.

“As the study notes, high levels of caffeine during pregnancy can lead to miscarriage and babies having a low birth weight and may lead to excess weight gain in the child’s early years, which can increase risk of health problems later in life. However, as other – and potentially more reliable – research has found, pregnant women do not need to cut caffeine out entirely because these risks are extremely small, even if the recommended caffeine limits are exceeded.

“The Royal College of Obstetricians and Gynaecologists’ advise to limit caffeine intake to 200 milligrams (mg) per day – the equivalent to two cups of instant coffee – still stands.”

While some pregnant women may prefer to err on the side of caution and cut out caffeine completely, for the time being those who can’t do without their daily cup of java may prefer to stick to the current official advice and drink no more than 200mg per day.

How much caffeine is in your food and drink?

Very high caffeine intake is usually defined as 300mg or more per day

High caffeine intake is defined as 200–299mg per day

Average caffeine intake is defined as 50-199mg per day

Low caffeine intake is defined as less than 50mg per day

Source: Mayo Clinic and USDA