35.5 PERINATAL RISK FACTORS OF ATTENTION-DEFICIT/HYPERACTIVITY DISORDER: A POPULATION-BASED STUDY

Objectives: Previous studies have shown associations between perinatal risk factors and ADHD. The results are partly controversial, and some of the obstetric factors have not been studied previously in a population-based setting. In this study, our objective was to examine the association of a variety of prenatal, birth-related, and newborn risk factors and subsequent ADHD diagnoses in a nationwide epidemiological frame. Methods: In this population-based study, 10,409 children diagnosed with ADHD, according to International Classification of Disease criteria, and 39,124 control subjects, individually matched for sex, date of birth, and place of birth, were identified from Finnish nationwide registry. Perinatal data was obtained from the Finnish Medical Birth Register. Conditional logistic regression was used to examine the association between prenatal, birth-related, and newborn risk factors and ADHD after controlling extensively for confounding factors. Results: We identified several perinatal risk factors for ADHD. Declining Apgar scores increased the risk of ADHD. Elective cesarean section remained a risk factor for ADHD after controlling for confounding factors. Other identified risk factors included mother's high blood pressure, nulliparity, breech presentation, induction of labor, and the child being treated in a neonatal intensive care unit. Low umbilical artery pH did not increase the risk of ADHD. Conclusions: Perinatal adversities leading to lower Apgar score increase the risk of ADHD, whereas low umbilical pH does not seem to predict later ADHD. Future research is warranted to untangle the mechanisms behind these associations. The increased risk of ADHD with elective cesarean section should be taken into account while planning the appropriate mode of delivery.