In Denmark, the municipal health care system offers all families with newborn children a series of home visits delivered free of charge by a community health nurse (CHN) . CHNs are registered nurses with a 1½ year further education comprising training in assessment of health and development in children. Approximately 97% of all families participate in these home visits. Most municipalities comply with recommendations from the National Health Authority and offer at least five home visits (a) a few days after delivery, (b) 1-2 weeks, (c) 2-3 months, (d) 4-6 months and (e) 8.10 months after delivery. CHNs in a range of municipalities have organized a clinical database – the Child Health Database - with standardized data from their records. The health visitors apply a manual of definitions to ensure comparability and stimulate validity of data in their records. The records include the child’s unique person identification number which make it possible to link data with data from national health and sociodemographic registers which cover the total population in Denmark.
Study design and study population: Longitudinal study of children from birth to their 8th birthday using clinical data from the Child Health Database and register data from the National Birth Register, the Danish National Patient Register, and the Civil Registration System. Inclusion criteria: 1) All children from 16 municipalities in the Copenhagen region in Denmark born between 1st January 2002 and 31st December 2010 and having their 8th birthday before 1st January 2019 (n=47,167) and 2) included in the Child Health Database. Exclusion criteria: 1) Mental disorder diagnosed at hospital within the first 10 months of the child’s life (n=946); 2) missing data on motor development problems (n=8,634) or any applied control variable (n=4,349), leaving a final sample of 33,238 children.
Measures: The predictor variable was problems of motor development problems assessed by the CHN at the scheduled home visit at child age 8-10 months. According to the guidelines and the manual for assessments at ages 8-10 months, the health visitor expressed a concern in the record if the child did not meet all these specific developmental milestones: Unable to roll over from back to stomach and reverse, unable to sit independently, unable to move things from hand to hand, do not put things into the mouth, unable to crawl forwards and/or backwards, unable to pull to a standing position. We summarized the assessment into a dichotomous variable, +- motor development problems.
The outcome variable was any mental disorder diagnosed in hospital settings from child age 11 months to the 8th birthday, obtained from the Danish National Patient Register which includes all in- and outpatient and emergency hospital contacts with a 100% coverage . In these settings, medical doctors conclude on the clinical and paraclinical data to diagnose mental disorders in accordance with the defining criteria of the International Classification of Mental and Behavioral Disorders 10 (ICD-10) . We included the range of mental disorders seen in childhood: General developmental disorders or disorders of intellectual disability (F70-F79), specific developmental disorders (F 80-83), pervasive and other developmental disorders (F84-89), hyperkinetic disorders (F90), attention deficit disorder without hyperactivity (F98.8), mood disorders, emotional and stress-related disorders (F30-F34, F38-F45, F48, F 93), disorders of eating and sleep (F50-F51, F 98.2), and disorders of behaviour (F91-F92) and of social functioning (F94.1-F94.2, F94.8). We summarized the data into three dichotomous variables, diagnosed neuro-developmental disorder including disorders of ID, ASD and ADHD (yes, no), diagnosed behavioural or emotional disorder (yes, no), and at least one diagnosed mental disorder before the age of 8 years (yes, no).
The analyses included the following potential confounders: From the National Birth Register: Sex, parity, gestational age (born 37th week or later vs. before); birth weight (<2500 g, 2500-3999 g, >3999 g); congenital malformation (yes, no); mother’s and father’s age at childbirth (<25 vs. ≥25); pregnancy complications (yes, no); cesarian section (yes, no); and Apgar score (9-10 vs. less). From the Civil Registration System: parents’ education at childbirth (five levels); parents’ employment (2, 1 or 0 employed parents), family composition (child lives with both parents, yes vs. no), and parents’ origin (2, 1 or 0 parents of Danish origin). From the Child Health Database: Concern about mother’s mental health in the first six months after delivery (concern at 0 vs. at least one home visit); and concerns about the parent-child-relationship in the first six months after delivery (concern at 0 vs. at least one home visit).
The first step was contingency tables for inspection of data and use of chi2-test for heterogeneity (not shown in table). The second step was logistic regression analysis of the association between motor development problems at age 8-10 months and diagnosed mental disorder from age 11 months to the 8th birthday, adjusted for all potential confounder variables.