Aims: To investigate associations between maternal blood concentrations of selenium, mercury and lead and childhood respiratory and atopic outcomes, and interactions with paracetamol and GST, GCL and GPx polymorphisms. Hypotheses:1) Maternal mercury and lead concentrations in blood in pregnancy are positively associated with atopic outcomes in the offspring.2) Maternal mercury may partly explain the associations of higher socioeconomic status and birth order/parity with childhood atopy.3) Associations with mercury will be modified by GST/GCLC variants in the mother and child, by maternal blood selenium and by paracetamol use in pregnancy. Also, paracetamol effects on asthma and IgE will be modified by mercury exposure.4) Maternal blood concentrations of selenium will be positively associated with wheezing and asthma in the offspring and this relation will be modified by the GPx4 gene variant in mother and child and also by mercury concentrations and by maternal intake of vitamin E.5) A high Hg/Se ratio will be positively associated with atopy; a high Se/Hg ratio will be negatively associated with wheezing and asthma. Primary exposures (data requested): Maternal blood concentrations of Se, Hg and Pb in pregnancy. Outcomes of interest: childhood respiratory and atopic outcomes (data already available). Prenatal and postnatal confounders (data already available).