International guidelines recommend people limit how much coffee they drink during pregnancy. Consuming caffeine - a stimulant - while pregnant has been linked to how the baby's brain develops.
Authors
Gunn-Helen Moen
Post-doctoral research fellow in genetic epidemiology, The University of Queensland
Shannon D'Urso
PhD candidate, Institute of Molecular Biology, The University of Queensland
Some studies have shown increased coffee consumption during pregnancy is associated with the child having neurodevelopmental difficulties. These may include traits linked to attention-deficit hyperactivity disorder (ADHD), such as difficulties with language, motor skills, attention, hyperactivity and impulsive behaviour.
But is coffee the cause? Our new research aimed to clear up the sometimes confusing advice about drinking coffee during pregnancy.
We studied tens of thousands of pregnant women over two decades. The results showed - when other factors like genes and income were accounted for - no causal link between drinking coffee during pregnancy and a child's neurodevelopmental difficulties. That means it's safe to keep drinking your daily latte according to current recommendations.
What we were trying to find out
Past research has identified a link between drinking coffee during pregnancy and a child's neurodevelopmental difficulties. But it hasn't been able to establish caffeine as the direct cause.
Biological changes during pregnancy reduce caffeine metabolism. This means the caffeine molecules and metabolites (the molecules produced while breaking down the caffeine) take longer to be cleared from the body.
Additionally, past studies have shown caffeine and its by-products can cross the placenta. The fetus does not have the necessary enzymes to clear them, and so it was thought that caffeine metabolites may impact the developing baby.
However it can be hard to identify whether coffee directly causes changes to the fetus's brain development. Pregnant women who drink coffee may differ from those who don't in a number of other ways. And it could be these variables - not coffee - that affect neurodevelopment.
These variables, known as "confounding factors" might include how much people drink or smoke while pregnant, or a parent's income and education. For example, we know people who tend to drink coffee also tend to drink more alcohol and smoke more cigarettes than those who don't drink coffee.
Our study aimed to look at the effect of drinking coffee on neurodevelopmental difficulties, isolated from these confounding factors.
What we did
We know genes play a role in how many cups of coffee a person consumes per day. Our study used genetics to compare the development of children whose mothers did and did not carry genes linked to increased coffee consumption.
The study looked at tens of thousands of families registered in the Norwegian Mother, Father and Child Cohort Study. All pregnant women in Norway between 1999 and 2008 were invited to participate and 58,694 women took part with their child.
Parents reported how much coffee they drank before and during pregnancy. Mothers also completed questionnaires about their child's neurodevelopmental traits between six months and eight years of age.
The questions covered many traits, including difficulties with attention, communication, behavioural flexibility, regulation of activity and impulses, as well as motor and language skills.
The parents and children also provided genetic samples. This allowed us to control for genetic variants shared between mother and child and isolate the behaviour of coffee drinking.
What we found
We were able to look at causality through this method of adjusting for potential confounding factors in the environment (the mother smoking or drinking alcohol, the parents' education and income).
The results showed no strong causal link between increased maternal coffee consumption and children's neurodevelopmental difficulties.
The difference in findings between our and previous studies may be explained by our work separating the effect of coffee from the effect of other variables, as well as genetic predisposition to neurodevelopmental conditions.
Our study has limitations. Importantly, we were only able to rule out strong effects of coffee on neurodevelopmental difficulties, and it is possible small effects may exist.
We only investigated offspring neurodevelopmental traits, and coffee consumption during pregnancy could impact the mother or child in other ways.
However we have previously shown coffee consumption during pregnancy did not have strong causal effects on birth weight, gestational duration, risk of miscarriage or stillbirth. But other outcomes - such as mental health or a child's risk for heart disease and stroke later in life - should be investigated.
Overall, our study supports current clinical guidelines that state low to moderate consumption of coffee during pregnancy is safe for the mother and developing baby.
For most people, that means sticking below 200mg of caffeine per day - usually equivalent to one espresso or two instant coffees - should be safe. If you have concerns, it's best to speak to your clinician.
Gunn-Helen Moen receives funding from the Australian Research Council and the Research Council of Norway.
Shannon D'Urso does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.
