Koopman LP, van Strien RT, Kerkhof M, et al. Am J Respir Crit Care Med. 2002;166:307–313 To look at the effect of using house dust mite impermeable mattress covers on the development of respiratory symptoms, atopic eczema, and mite sensitization in children born to mothers with allergy. This study is a report from the Prevention and Incidence of Asthma and Mite Allergy (PIAMA) study which has been conducted in a number of European centers. There were a total of 1282 pregnant women who participated. These women were randomized to the intervention study ([IS]; n = 810) or the natural history study ([NHS]; n = 472). The IS group was further divided into active treatment ( n = 416) or placebo treatment ( n = 394). Active treatment consisted of the use of polyester-cotton allergen impermeable covers for the mattress and pillows of the mother during the third trimester of pregnancy. The infant’s mattresses were also covered. The placebo group was given cotton covers only. Both the parents and the investigators were blinded as to group assignment. Absolutely no intervention occurred in the NHS. This group served as a second control group. Questionnaires were used during pregnancy and when the child was 3 months …