Breaking the myth, a new systematic review and meta-analysis led by University of Bristol researchers show that maternal prenatal smoking is associated with offspring attention-deficit hyperactivity disorder (ADHD) but is unlikely to be the cause of it.

The study was published in the scientific journal Addiction. Several studies have indicated that maternal smoking during pregnancy may contribute to offspring ADHD; however, it is unclear from those studies whether this reflects a true causal effect or is the result of confounding factors such as socioeconomic position, education, income and maternal age. This new review attempted to find an answer to that question.

The review looked at 46 prior studies that assessed the association between maternal prenatal smoking and offspring ADHD diagnosis. The review specifically included studies accounting for genetic effects, in addition to conventional approaches.

Some of those studies had a low risk of bias (meaning they are unlikely to give misleading results) and were able to take into account genetic effects. Those studies indicate that shared genetics plays a substantial role in the association of offspring ADHD with prenatal smoking.

This is supported by a previous systematic review based on genetically informed designs which also concluded that the association between maternal prenatal smoking and ADHD is explained by shared genetics.

Lead author Dr Elis Haan, an Honorary Research Associate at Bristol's School of Psychological Science, says "Our systematic review shows that there is no causal effect between maternal prenatal smoking and offspring ADHD diagnosis. However, pregnant women should still be advised not to smoke during pregnancy, as prenatal smoking has harmful effects on other child health outcomes."