Objective: To study if factors at birth are associated with later development of atopic dermatitis. Design: Historical follow up by record linkage from Danish medical birth register. Children were followed up for 5.5 to 8.5 years. Second historical follow up study comprising questionnaire to mothers of singleborn children 6.5 to 9.5 years after birth. Setting: Private dermatology clinics and dermatology and paediatric departments in the municipality of Aarhus, Denmark, Subjects: 7862 singletons born in hospital between 1 January 1984 and 31 December 1986 to mothers living in the municipality of Aarhus. Questionnaires sent to 985 mothers. Main outcome measures: Gestational age, birth weight, parity, and age of mother at the time of birth. Atopy in children diagnosed by specialists in dermatology and physicians. Family size; diagnosis of atopic dermatitis, allergic rhinitis, and asthma; family predisposition; and mothers' smoking habits during pregnancy determined from questionnaires. Results: Of 7862 children, 403 were diagnosed as having atopic dermatitis by a specialist; the cumulative incidence at age 7 was 5.6%. High gestational age and low parity were associated with an increased risk of atopic dermatitis, Among 985 children atopic dermatitis had been diagnosed by any physician in 184; the cumulative incidence at age 7 was 18.7%. High birth weight high gestational age, and family history of atopy were associated with increased risk of atopic dermatitis. Conclusion: In both studies the incidence of atopic dermatitis was associated with high gestational age and in one with high birth weight also. The causes for these associations are at present unknown but may indicate that even during gestation factors associated with atopic dermatitis influence maturation.
