Birth order and sibship size as independent risk factors for asthma, allergy, and eczema

This study was carried out to disentangle the independent relations of birth order and sibship size with the presence of asthma, allergy and eczema. In a retrospective study, 700 families in the Netherlands were selected with index children born in 1988–90. Data were extracted from reports of health examinations at the age of 6 years of these children and their siblings. Birth order, and not sibship size, appeared to be a strong risk factor for allergy (excluding eczema). Children with higher birth order had a lower risk of allergy compared with first‐borns (adjusted odds ratios: 0.43, 0.26 and 0.05 for second‐, third‐ and fourth‐ or higher borns, respectively; p