Incidence rates of treated mental disorders before and during the COVID-19 pandemic-a nationwide study comparing trends in the period 2015 to 2021.

BACKGROUND: There is a concern that exposure to psychosocial stressors during the COVID-19 pandemic may have led to a higher incidence of mental disorders. Thus, this study aimed to compare trends in incidence rates of depressive disorder, anxiety disorders, obsessive-compulsive disorder (OCD), post-traumatic stress disorder (PTSD), and eating disorders in primary- and specialist health care before (2015-2019) and during the COVID-19 pandemic (2020-2021). METHODS: We used aggregated population registry data to calculate incidence rates of mental disorders from primary- (The Norwegian Control and Payment of Health Reimbursements Registry (KUHR)) and specialist (The Norwegian Patient Registry (NPR)) health care. The analyses included all Norwegian residents aged 18-65 during the study period. Incident cases were defined as having no previous registration with the same mental disorder in KUHR (from 2006) or NPR (from 2008). We used linear prediction models and mean models to compare incidence rates and test trends before and during the pandemic. RESULTS: During the pandemic, the incidence rates among women were higher or as predicted for OCD in specialist health care and for eating disorders in both primary- and specialist health care. These findings were strongest among women aged 18-24 years. Incidence rates for depression and phobia/OCD among both genders in primary health care and phobic anxiety disorders among both genders in specialist health care were lower or as predicted. CONCLUSION: The COVID-19 pandemic may have led to more women needing treatment for OCD and eating disorders in the Norwegian population. The decreased incidence rates for some disorders might indicate that some individuals either avoided seeking help or had improved mental health during the pandemic.

Contact with primary care physicians among adults with pre-existing common mental health problems during the COVID-19 pandemic: a registry-based study from Norway.

BACKGROUND: During the COVID-19 pandemic, individuals with pre-existing mental health problems may have experienced additional stress, which could worsen symptoms or trigger relapse. Thus, this study aimed to investigate if the number of consultations with general practitioners (GPs) among individuals with a pre-existing common mental health problem during the pandemic differed from pre-pandemic years. METHODS: Data on consultations with GPs among 18-65-year-olds registered with common mental health problems in 2017-2021 were retrieved from the Norwegian Control and Payment of Health Reimbursements Database. Based on data from the pre-pandemic years (2017-2019), we predicted the number of consultations per week for depression, anxiety disorder, phobia/obsessive-compulsive disorder (OCD), post-traumatic stress disorder (PTSD), and eating disorders during the pandemic (March 2020-December 2021) among individuals with pre-existing mental health problems. The forecasted and observed trends in GP consultations per week during the pandemic were stratified by diagnosis, gender, and age groups. RESULTS: The observed number of consultations for anxiety disorder, PTSD, and eating disorders were significantly higher than forecasted during extended periods of the two pandemic years. The differences were largest for PTSD (on average 37% higher in men and 47% higher in women during the pandemic), and for eating disorders among women (on average 87% higher during the pandemic). There were only minor differences between the predicted and observed number of consultations for depression and phobia/OCD. CONCLUSIONS: During the pandemic, individuals with a recent history of mental health problems were more likely to seek help for anxiety disorder, PTSD, and eating disorders, as compared to pre-pandemic years.

Maternal Anxiety and Infants Birthweight and Length of Gestation. A sibling design.

BACKGROUND: The overall aim of this study is to examine the effect of prenatal maternal anxiety on birthweight and gestational age, controlling for shared family confounding using a sibling comparison design. METHODS: The data on 77,970 mothers and their 91,165 children from the population-based Mother, Father and Child Cohort Study and data on 12,480 pairs of siblings were used in this study. The mothers filled out questionnaires for each unique pregnancy, at 17th and 30th week in pregnancy. Gestational age and birth weight was extracted from the Medical Birth Registry of Norway (MBRN). Associations between prenatal maternal anxiety (measured across the 17th and 30th weeks) and birth outcomes (birthweight and gestational age) were examined using linear regression with adjustment for shared-family confounding in a sibling comparison design. RESULTS: In the population level analysis the maternal anxiety score during pregnancy was inversely associated with new-born's birthweight (Beta = -63.8 95% CI: -92.6, -35.0) and gestational age (Beta = -1.52, 95% CI: -2.15, -0.89) after adjustment for several covariates. The association of the maternal anxiety score with birthweight was no longer significant, but remained for maternal anxiety at 30th week with gestational age (Beta = -1.11, 95% CI: -1.82, -0.4) after further adjusting for the shared-family confounding in the sibling comparison design. CONCLUSION: No association was found for maternal prenatal anxiety with birth weight after multiple covariates and family environment were controlled. However, there was an association between prenatal maternal anxiety at 30th week only with gestational age, suggesting a timing effect for maternal anxiety in third trimester.

Estimating the Strength of Associations Between Prenatal Diet Quality and Child Developmental Outcomes: Results From a Large Prospective Pregnancy Cohort Study.

Our aim in this study was to estimate the strength of associations between prenatal diet quality and child behavioral, language, and motor functions in the Norwegian Mother and Child Cohort Study (1999-2008). We created a prenatal diet quality index (PDQI) based on adherence to Norwegian dietary guidelines. Child outcomes were defined as sum scores on the Child Behavior Checklist, the Ages and Stages Questionnaire, and the Child Development Index at ages 18, 36, and 60 months. Using a longitudinal cohort study design and Bayesian hierarchical modeling, we estimated association strengths using inverse probability weighting to account for selection bias. In total, 27,529 mother-child pairs were eligible for inclusion. A 1-standard-deviation increase in PDQI score was associated with an absolute reduction in outcome sum scores of 0.02-0.21 and a 3%-7% relative decrease, with larger decreases seen for language and motor functions than for behavioral functions. PDQI scores were inversely associated with all child functions, but the estimated strength of each association was low. The results indicate that the observed variations in PDQI scores in an industrialized Western society may not profoundly influence the child functions studied.

Peer-Victimization of Young Children With Developmental and Behavioral Difficulties-A Population-Based Study.

OBJECTIVE: The aim is to investigate if young children with developmental and behavioral difficulties (DBDs) have greater risk of peer-victimization compared with typically developing (TD) children. METHOD: The sample was drawn from the Norwegian Mother and Child Cohort Study (MoBa). MoBa has collected population-based data on children's health and development for 114,500 children. We included children that were 5 years of age (n = 41,609). Multivariate logistic regression was used to estimate the effect of different DBDs and of co-occurring DBDs on peer-victimization compared with TD children. Categories of DBDs included autistic traits, emotional difficulties, behavioral difficulties, general learning difficulties, attention difficulties/impulsive behavior, motor development difficulties, language difficulties, and hearing and vision difficulties. Results were adjusted for socioeconomic status and the child's sex. RESULTS: Peer-victimization was 2.8% (933) among TD children, and 8.0% (615) among children with DBD. The highest risk of peer-victimization was found among children with autistic traits and children with five or more co-occurring DBDs (adjusted odds ratios [ORs] = 12.76; 95% confidence interval [CI] 8.64-18.84; p ≤ .001) and 17.37 (95% CI 12.15-24.82; p ≤ .001)], respectively. The lowest risk was found among children with hearing and vision difficulties and children with only one DBD [adjusted ORs = 1.98 (95% CI 1.71-2.29; p ≤ .001) and 1.95 (95% CI 1.70-2.22; p ≤ .001)]. CONCLUSION: Children with DBD have a substantially higher risk of peer-victimization compared with TD children. Peer-victimization varies with type of DBD and increases cumulatively by number of DBDs.

Language competence and communication skills in 3-year-old children after prenatal exposure to analgesic opioids.

PURPOSE: An increasing consumption of opioids in the general population has been reported in several countries also among pregnant women. Limited information is available regarding the effect of prenatal exposure to analgesic opioids on long-term neurocognitive function in children. The primary aim of the study was to determine the association between prenatal exposure to analgesic opioids and language competence and communication skills at 3 years of age. METHODS: The Norwegian Mother and Child Cohort Study (MoBa) prospectively included pregnant women during the period from 1999 to 2008. Participants reported medication use at pregnancy weeks 17-18 and 30, and 6 months after birth. Children's language competence and communication skills were reported by mothers on validated scales. RESULTS: A total of 45 211 women with 51 679 singleton pregnancies were included. The use of analgesic opioids was reported in 892 pregnancies (1.7%). In adjusted analyses, no association between opioid use and reduced language competence or communication skills was found, OR = 1.04 (95%CI: 0.89-1.22) and OR = 1.10 (95%CI: 0.95-1.27), respectively. Both pain and use of paracetamol were associated with a small reduction in communication skills. No such association was found for language competence. CONCLUSION: The use of analgesic opioids in pregnant women does not seem to affect language development or communication skills in children at 3 years of age. Copyright © 2017 John Wiley & Sons, Ltd.

Communication impairments in early term and late preterm children: a prospective cohort study following children to age 36 months.

OBJECTIVE: To investigate the risk of communication impairments at age 18 and 36 months in children born early term (gestational weeks 37-38) and late preterm (gestational weeks 34-36). STUDY DESIGN: A total of 39 423 children and their mothers participated in the Norwegian Mother and Child Cohort Study. The sample included 7109 children (18%) born early term and 1673 (4.2%) born late preterm. Information on gestational age and prenatal and postnatal risk factors was obtained from the Medical Birth Registry of Norway. Information on communication impairments was assessed using standardized questionnaires filled out by the mothers. Stepwise logistic regression analysis was applied to explore the associations between early term/late preterm birth and communication impairments at age 18 and 36 months. RESULTS: Compared with children born at term, children born early term and late preterm had an increased risk of communication impairments at age 18 and 36 months. In early term, the aOR was 1.27 (95% CI, 1.12-1.44) at 18 months for communication impairments and 1.22 (95% CI, 1.07-1.39) at 36 months for expressive language impairments. In late preterm, the aOR was 1.74 (95% CI, 1.41-2.14) at 18 months and 1.37 (95% CI, 1.09-1.73) at 36 months. CONCLUSION: Not only children born late preterm, but also those born early term, are at increased risk for communication impairments. Given the large number of children potentially affected, this may result in significant health care costs.

The role of early social play behaviors and language skills for shy children's later internalizing difficulties in school.

Research has demonstrated links from early childhood shyness to socioemotional problems later in life. This longitudinal study explored the role of early social play behaviors and language skills in the associations between childhood shyness and later internalizing and language difficulties in school. Participants were N = 7,447 children (50.1% girls) from the Norwegian Mother, Father, and Child Cohort Study (MoBa). Latent direct, indirect, and interaction path analyses were performed within a structural equation framework. Results showed that mother-rated childhood shyness from age 18 months to age five years was associated with mother-rated internalizing difficulties and language problems at age eight years. Lower levels of teacher-reported social play behaviors and poorer language skills in preschool increased the risk of later anxiety problems among shy children, whereas higher levels of language competencies and social play behaviors buffered against later anxiety problems. The study identifies some of the early risk and protective factors that may influence shy children's socio-emotional functioning and adjustment.

Addressing Global Environmental Challenges to Mental Health Using Population Neuroscience: A Review.

Importance: Climate change, pollution, urbanization, socioeconomic inequality, and psychosocial effects of the COVID-19 pandemic have caused massive changes in environmental conditions that affect brain health during the life span, both on a population level as well as on the level of the individual. How these environmental factors influence the brain, behavior, and mental illness is not well known. Observations: A research strategy enabling population neuroscience to contribute to identify brain mechanisms underlying environment-related mental illness by leveraging innovative enrichment tools for data federation, geospatial observation, climate and pollution measures, digital health, and novel data integration techniques is described. This strategy can inform innovative treatments that target causal cognitive and molecular mechanisms of mental illness related to the environment. An example is presented of the environMENTAL Project that is leveraging federated cohort data of over 1.5 million European citizens and patients enriched with deep phenotyping data from large-scale behavioral neuroimaging cohorts to identify brain mechanisms related to environmental adversity underlying symptoms of depression, anxiety, stress, and substance misuse. Conclusions and Relevance: This research will lead to the development of objective biomarkers and evidence-based interventions that will significantly improve outcomes of environment-related mental illness.

Associations between poor gross and fine motor skills in pre-school and peer victimization concurrently and longitudinally with follow-up in school age - results from a population-based study.

BACKGROUND: Children with poor motor skills are at increased risk of peer victimization. However, it is unclear whether poor gross and fine motor skills are differently linked to peer victimization among pre-school and schoolchildren. AIMS: To investigate associations between poor gross and fine motor skills measured in pre-school and the associations to peer victimization measured concurrently and in school age. SAMPLE: Data from the Norwegian Mother, Father and Child Cohort Study (MoBa), and the Medical Birth Registry of Norway were used. Participants with complete questionnaires at 3, 5, and 8 years (n = 23 215) were included. METHODS: A longitudinal design and an autoregressive cross-lagged model were used to investigate if poor gross and fine motor skills at 3 and 5 years predicted peer victimization at 5 and 8 years. Because emotional difficulties are associated with both motor skills and peer victimization, the results were adjusted for emotional difficulties. RESULTS: Only poor fine motor skills at 3 years had a significant association to peer victimization at 5 years. Poor gross motor skills at 5 years had a stronger association to peer victimization measured concurrently compared to poor fine motor skills, and only poor fine motor skills at 5 years was significantly linked to peer victimization at 8 years. No gender difference was found between these paths. CONCLUSIONS: Teachers and parents should be aware that motor skills predict peer victimization, and that poor gross and fine motor skills have different associations to peer victimization measured at different ages.

Association between work situation and life satisfaction during the COVID-19 pandemic: prospective cohort study in Norway.

OBJECTIVES: To estimate the impact of being laid off from work, having to work from home or having been diagnosed with COVID-19 on self-reported satisfaction with life. DESIGN: Nationwide population-based cohort study. SETTING: Norway. PARTICIPANTS: We followed more than 80 000 participants in an ongoing cohort study, the Norwegian Mother, Father and Child Cohort Study (MoBa), during the COVID-19 pandemic. We analysed current life satisfaction in April and again in September/October 2020 for subjects whose work situation and infection status had changed. MAIN OUTCOME MEASURES: Self-reported satisfaction with life, using a scale from 0 (worst) to 10 (best). We analysed the scale both continuously and as a binary variable (

Mild-to-moderate iodine deficiency and symptoms of emotional distress and depression in pregnancy and six months postpartum - Results from a large pregnancy cohort.

BACKGROUND: The relationship between iodine intake and depression is unknown. The aim of the present study was to investigate whether iodine intake was associated with symptoms of perinatal emotional distress and depression in a mild- to moderately iodine deficient population. METHODS: The study population comprised 67,812 women with 77,927 pregnancies participating in the Norwegian Mother, Father and Child Cohort Study. Self-reported emotional distress and depressive symptoms were reported in pregnancy and at six months postpartum. Iodine intake was assessed by a food frequency questionnaire in mid-pregnancy. Urinary iodine concentration (UIC) was available for 2792 pregnancies. RESULTS: The median iodine intake from food was 121 µg/day and the median UIC was 68 µg/L. The prevalence of high scores for emotional distress was 6.6 % in pregnancy and 5.8 % six months postpartum, and for high scores on postpartum depression it was 10.3 %. In non-users of iodine supplements (63 %), a low maternal iodine intake from food (lower than ~100-150 µg/day) was associated with increased risk of high scores of emotional distress and depression both in pregnancy and six months postpartum (p < 0.001). Iodine supplement use was associated with increased risk of high scores of emotional distress in pregnancy compared to no supplement use or use of supplements without iodine. LIMITATIONS: Observational design, self-report information, and short scales to assess symptoms of emotional distress and depression. CONCLUSION: A low habitual iodine intake was associated with increased prevalence of perinatal emotional distress and depression. The potential non-beneficial effect of iodine supplements may have biological explanations. More studies are needed.

Longitudinal findings from a Norwegian case-cohort study on internalizing problems in children with congenital heart defects.

AIM: To examine the association of the severity of congenital heart defects (CHDs) with internalizing problems in 18-month-olds and to explore the extent to which the internalizing problems are influenced by maternal distress and emotional reactivity in the child at age 6 months. METHODS: We linked prospective data from the Norwegian Mother and Child Cohort Study, conducted by the Norwegian Institute of Public Health, with a nationwide CHD registry and identified 198 18-month-olds with CHDs in a cohort of 47 692 toddlers. Maternal reports on the children's emotional reactivity at age 6 months, the children's internalizing problems (anxiety, sleep problems, emotional reactivity) at age 18 months and maternal distress were assessed by questionnaires. RESULTS: We found an association at age 18 months between the severity of the CHD and anxiety but not sleep problems or emotional reactivity. Children with severe but not with mild or moderate CHDs were twice as likely to experience the symptoms of anxiety compared with controls. These symptoms are not merely sequelae of earlier psychological reactions or concurrent maternal distress. CONCLUSION: Should these findings be replicated, future studies ought to investigate the mechanisms leading to elevated anxiety in toddlers with CHDs. In addition, clinical interventions should address the child's anxiety as well as the interaction between the parents and the child.

Associations Between Language Difficulties, Peer Victimization, and Bully Perpetration From 3 Through 8 Years of Age: Results From a Population-Based Study.

Background and Purpose Schoolchildren with language difficulties experience more peer victimization compared to their typically developing (TD) peers. Whether these children also bully their peers (bully perpetration) more than TD children is unclear. Furthermore, little is known about peer victimization and bully perpetration among preschool children with language difficulties and how it may be related to different paths of language difficulties. This study aimed to investigate associations between language difficulties, peer victimization, and bully perpetration from preschool to school age as well as the risk of peer victimization and bully perpetration for children with different developmental paths of language difficulties and mild language difficulties compared to TD children. Method The sample was drawn from the Norwegian Mother, Father and Child Cohort Study. Participants with completed questionnaires at 3, 5, and 8 years of age (n = 22,628) were included. Paths between latent variables of language skills at 3, 5, and 8 years of age, peer victimization at 5 and 8 years of age, and bully perpetration at 8 years of age were examined with structural equation modeling. Logistic regression was used to investigate peer victimization and bully perpetration for predefined paths of language difficulties. Results Poor language skills at 3 and 5 years of age were associated with peer victimization at 5 years of age. Poor language skills at 5 and 8 years of age were associated with peer victimization and bully perpetration at 8 years of age. The association between poor language skills at 5 years of age and bully perpetration at 8 years of age was stronger for girls. Persistent paths of language difficulties at 3, 5, and 8 years of age showed the highest risk of peer victimization and bully perpetration. Conclusions Language difficulties are associated with peer victimization and bully perpetration. The risk of peer victimization and bully perpetration differs according to different developmental paths of language difficulties from preschool to school age.

Motor and social development in 6-month-old children with congenital heart defects.

OBJECTIVE: To assess whether the development of children with varying severity of congenital heart defect (CHD) differs from that of children without CHD at age 6 months. STUDY DESIGN: A total of 236 children with CHD were compared with 61 032 children from the Norwegian Mother and Child Cohort Study conducted by the Norwegian Institute of Public Health. Diagnostic and treatment information was retrieved from a nationwide CHD registry. Four groups of CHD were distinguished: mild (n = 92), moderate (n = 50), severe (n = 70), and CHD with comorbidity (n = 24). At child age 6 months, the children's mothers reported on motor and social development by using the Mother and Child Questionnaire. RESULTS: After adjusting for confounders (ie, birth weight), severe CHD increased the odds of gross motor impairment (odds ratio [OR], 3.78; 95% CI, 1.97-7.25) and fine motor impairment (OR, 2.04; 95% CI, 0.96-4.33). CHD with co-morbidity (eg, intestinal malformations) increased the odds of gross motor impairment (OR, 3.00; 95% CI, 0.95-9.51), fine motor impairment (OR, 5.47; 95% CI, 2.03-14.74), and social impairment (OR, 3.43; 95% CI, 1.40-8.41). CONCLUSION: Increased odds of motor impairment are present already in infancy in severe CHD and CHD with comorbidity. CHD with comorbidity increases the odds of social impairment.

A Common Family Factor Underlying Language Difficulties and Internalizing Problems: Findings From a Population-Based Sibling Study.

Studies have identified concurrent, longitudinal, and bidirectional associations between language difficulties and internalizing problems. This is commonly explained by social exclusion or withdrawal from peers, but underlying mechanisms are not well understood. This study uses sibling data to investigate if the comorbidity between language difficulties and internalizing problems is best explained by familial factors shared by siblings, such as genes or family environment, or nonfamilial factors specific to each child, such as peer environment. Data include 5,568 siblings at 5 years and 3,654 siblings at 8 years participating in the Norwegian Mother, Father and Child Cohort Study (MoBa). We constructed a latent factor model at 5 and 8 years, including a family comorbidity factor capturing correlations between language and internalizing problems that were equally strong between as within siblings. Results showed that the correlation between one sibling's internalizing problems and the other sibling's language problems was mostly accounted for by a family comorbidity factor. The best-fitting longitudinal model included stability of the family comorbidity factor and stability of language and internalizing problems within each sibling and no cross-sibling or cross-trait longitudinal associations. This suggests that the association between language and internalizing problems may be best explained by family factors.

Factors associated with pharmacy students' attitudes towards learning communication skills - A study among Nordic pharmacy students.

INTRODUCTION: Good communication skills are essential for pharmacy students to help patients with their medicines. Students' attitudes towards communication skills learning will influence their willingness to engage in communication training, and their skills when dealing with patients later on in their professional life. OBJECTIVE: The aim of this study was to explore Nordic pharmacy students' attitudes to communication skills learning, and the associations between those attitudes and various student characteristics. METHOD AND MATERIALS: A cross-sectional questionnaire-based study was conducted in 11 Nordic pharmacy schools between April 2015 and January 2016. The overall response rate for the final study population was 77% (367 out of 479 students). Pharmacy students who had fulfilled all mandatory communication training and most of their pharmacy practical experience periods were included. The communication skills attitudes scale was the main outcome. Linear regression models were fitted with the outcome variable and various student characteristics as the predictors, using generalized estimating equations to account for clustering within pharmacy schools. RESULTS: Nordic pharmacy students in general have moderately positive attitudes towards learning communication skills. Positive attitudes towards learning communication skills among pharmacy students were associated with being female (ßadjusted 0.42, 95% CI 0.20 to 0.63, p < 0.001), following a newer pharmacy training program (ßadjusted 0.81, 95% CI 0.63 to 0.98, p < 0.001), having higher self-rated need for communication skills improvement (ßadjusted 0.50, 95% CI 0.30 to 0.71, p<0.001) and believing one's communication skills are not the result of personality (ßadjusted -0.24, 95% CI -0.44 to -0.04, p=0.017). CONCLUSION: The study provides important information for faculty members responsible for curriculum improvements and teachers to refine their teaching of communication skills. From this, the teaching can be better tailored to suit different students. The students' chances of being able to effectively help patients in the future will be increased by that.

Prenatal mercury exposure, maternal seafood consumption and associations with child language at five years.

BACKGROUND: Methyl mercury (MeHg) is a well-known neurotoxin and evidence suggests that also low level exposure may affect prenatal neurodevelopment. Uncertainty exists as to whether the maternal MeHg burden in Norway might affect child neurodevelopment. OBJECTIVE: To evaluate the association between prenatal mercury exposure, maternal seafood consumption and child language and communication skills at age five. METHODS: The study sample comprised 38,581 mother-child pairs in the Norwegian Mother and Child Cohort Study. Maternal mercury blood concentration in gestational week 17 was analysed in a sub-sample of 2239 women. Prenatal mercury exposure from maternal diet was calculated from a validated FFQ answered in mid-pregnancy. Mothers reported children's language and communications skills at age five by a questionnaire including questions from the Ages and Stages Questionnaire (ASQ), the Speech and Language Assessment Scale (SLAS) and the Twenty Statements about Language-Related Difficulties (language 20). We performed linear regression analyses adjusting for maternal characteristics, nutritional status and socioeconomic factors. RESULTS: Median maternal blood mercury concentration was 1.03µg/L, dietary mercury exposure was 0.15µg/kgbw/wk, and seafood intake was 217g/wk. Blood mercury concentrations were not associated with any language and communication scales. Increased dietary mercury exposure was significantly associated with improved SLAS scores when mothers had a seafood intake below 400g/wk in the adjusted analysis. Sibling matched analysis showed a small significant adverse association between those above the 90th percentile dietary mercury exposure and the SLAS scores. Maternal seafood intake during pregnancy was positively associated with the language and communication scales. CONCLUSION: Low levels of prenatal mercury exposure were positively associated with language and communication skills at five years. However, the matched sibling analyses suggested an adverse association between mercury and child language skills in the highest exposure group. This indicates that prenatal low level mercury exposure still needs our attention.

Prenatal Exposure to Acetaminophen and Risk of ADHD.

OBJECTIVES: To estimate the association between maternal use of acetaminophen during pregnancy and of paternal use before pregnancy with attention-deficit/hyperactivity disorder (ADHD) in offspring while adjusting for familial risk for ADHD and indications of acetaminophen use. METHODS: Diagnoses were obtained from the Norwegian Patient Registry for 112 973 offspring from the Norwegian Mother and Child Cohort Study, including 2246 with ADHD. We estimated hazard ratios (HRs) for an ADHD diagnosis by using Cox proportional hazard models. RESULTS: After adjusting for maternal use of acetaminophen before pregnancy, familial risk for ADHD, and indications of acetaminophen use, we observed a modest association between any prenatal maternal use of acetaminophen in 1 (HR = 1.07; 95% confidence interval [CI] 0.96-1.19), 2 (HR = 1.22; 95% CI 1.07-1.38), and 3 trimesters (HR = 1.27; 95% CI 0.99-1.63). The HR for more than 29 days of maternal acetaminophen use was 2.20 (95% CI 1.50-3.24). Use for <8 days was negatively associated with ADHD (HR = 0.90; 95% CI 0.81-1.00). Acetaminophen use for fever and infections for 22 to 28 days was associated with ADHD (HR = 6.15; 95% CI 1.71-22.05). Paternal and maternal use of acetaminophen were similarly associated with ADHD. CONCLUSIONS: Short-term maternal use of acetaminophen during pregnancy was negatively associated with ADHD in offspring. Long-term maternal use of acetaminophen during pregnancy was substantially associated with ADHD even after adjusting for indications of use, familial risk of ADHD, and other potential confounders.