We studied the effects of preconceptional allergen sensitisation and repeated airway allergen challenges during pregnancy on maternal immune and airway functions during pregnancy, and maternal, fetal and placental phenotype in late pregnancy in sheep.This protocol induced maternal responses consistent with an allergic asthmatic phenotype. During pregnancy, lung resistance and the eosinophil influx induced by allergen challenges increased progressively in allergic sheep, and in late pregnancy airway smooth muscle content was greater in allergic than control ewes.Effects on fetal growth and development were consistent with those of maternal asthma in humans. Maternal allergic asthma decreased relative fetal weight by 12%, reduced fetal lung expression of surfactant protein B, and altered placental morphology.This provides an animal model in which to identify mechanisms underlying fetal effects of maternal asthma in pregnancy, including fetal physiological responses to exacerbations, and to evaluate responses to clinically used treatments and novel interventions.