Prenatal smoking exposure, measured as maternal serum cotinine, and children's motor developmental milestones and motor function: A follow-up study.

Background: Cohort studies have indicated an association between prenatal smoking exposure and children's motor difficulties. However, results are inconsistent and exposure is most often self-reported. Studies indicate that measurement of serum cotinine can result in a more accurate status of smoking exposure in comparison with self-report.

Objectives: To investigate whether prenatal smoking exposure, measured as maternal serum cotinine, is associated with maternal interview based assessment of motor development in infancy (age at crawling, standing-up and walking) and motor skills at young school age (assessed by the Developmental Coordination Disorder Questionnaire 2007 (DCDQ'07)).

Method: In 2002-2004, 1,253 pregnant women from Greenland and Ukraine were included in the INUENDO birth cohort. The participating women filled in questionnaires and 1,177 provided blood samples, which were analyzed for serum cotinine. Smokers were defined as women with a serum cotinine concentration >10ng/ml. At follow-up when the offspring were 6-9 years of age 1,026 of the parents from the cohort participated. They completed an interview-based questionnaire including questions about age at motor milestones of their children. In addition, child motor development was assessed using the questionnaire "DCDQ'07". Linear regression analyzes were performed and adjusted for covariates; age of the mother and child, parity, sex, maternal educational level, maternal pre-pregnancy alcohol consumption and duration of breastfeeding. Data were stratified by country.

Results: No statistically significant difference in age at motor milestones was found comparing children of smokers with children of non-smokers. Also, there was no statistically significant difference in motor score (Developmental Coordination Disorder Questionnaire Score, DCDQ-score) among five to seven-year-old children. However, in Greenland children of smokers had a lower DCDQ-score than children of non-smokers at eight to nine years (-2.2 DCDQ points, 95% CI: -4.3;-0.1). Supplementary results for the same age group in Greenland showed that children of smokers had higher odds of being classified with motor difficulties in comparison with children of non-smokers (OR=1.9, 95% CI: 1.1;3.3).

Conclusion: Maternal serum cotinine was not related to delayed motor development milestones or reduced motor function abilities in children up to 7 years of age. Reduced motor skills observed in 8-9 years old exposed children warrant further study.