Several studies, based on self-reports, have shown an association between maternal smoking during pregnancy and attention-deficit/hyperactivity disorder (ADHD) in offspring. A case-control study using blood samples reinforces that connection, providing new data that ob/gyns can use in prenatal counseling.
Published in Pediatrics, the population-based study enrolled 1079 patients born between 1998 and 1999 who were diagnosed with ADHD along with 1079 matched controls. The participants were identified from Finnish nationwide registers (Finland and the United States have similar rates of maternal smoking during pregnancy [~7%]). Maternal cotinine was measured from quantitative immunoassays from maternal blood samples that had been collected during the first and second trimesters and stored in the national biobank.
A significant association was found between levels of cotinine and offspring ADHD diagnosis. Mean cotinine levels were 27.4 ng/mL among patient with ADHD versus 11.3 ng/mL among controls. The odds ratio [OR] was 1.09 (95% CI 1.06-1.12) after adjustment for maternal socioeconomic status, maternal age and psychopathology, paternal age and psychopathology, and the child’s birthweight. When the authors classified the participants by level of cotinine exposure, heavy exposure (> 50 ng/mL) was associated most strongly with ADHD diagnosis [adjusted OR: 2.21, (95% CI: 1.63-2.99)].
The authors believe that their results are important for two reasons. First, they illustrate the viability of using cotinine as a means for measuring nicotine exposure during pregnancy rather than relying on self-reporting, which is often unreliable. The second reason is that this study shows a dose-response effect for nicotine exposure and ADHD diagnosis, meaning that the higher the level of nicotine in a mother’s blood during pregnancy, the more likely her child will be diagnosed with ADHD.