The incidence of allergic disease has increased worldwide during the last decades. Initially, a lot of effort has been put in elucidating which of the known risk factors commonly associated to the development of allergic disease early in life was the cause of this increase. Studies showing a reduced incidence of allergic disease in the former socialist countries in comparison to countries with a "Western lifestyle" have shown that risk factors as allergen exposure, environmental pollution and tobacco exposure are also present in societies with a less affluent lifestyle. This suggests the disappearance of factor protecting against the development of allergic diseases in affluent environment.The development of allergic diseases begins during the first year of life with eczema, both non-IgE- and IgE-associated, and food allergy, progressing during childhood with the development of asthma bronchiale, also both non-IgE- and IgE-associated, and later development of allergic rhinoconjunctivitis, i.e. the atopic march. The immune system of the neonate is influenced by maternal immunity, both via the placenta and breast milk. Thus, the immunological interaction between the mother and her offspring is close during pregnancy and lactation. The association of cord blood IgE levels with maternal but not paternal atopic heredity, may depend on a possibly stronger placental Th2 shift in atopic mothers. Thus, factors influencing/protecting against the development of allergic disease early in life, would be important already during pregnancy, birth and early postnatal life. Two major hypotheses have been assessed during the last decade: Proper microbial stimulation, including the establishment of the gut flora in infancy and the relationship between low omega 3-polyunsaturated fatty acids in the western diet and the incidence of allergic disease.

This is a double blind randomized study. Families with at least one parent/sibling with clinical symptoms/history of allergic disease will be invited to participate in this study. Pregnant mothers will be included in the study at the 20th week of gestation. They will be randomized to 4 study groups, one will receive placebo capsules, the second will receive omega-3 PUFA supplementation and placebo regarding L. reuteri, the third will receive L. reuteri and placebo regarding omega-3 PUFA and the fourth group will receive both omega-3 PUFA and L. reuteri supplementation. Omega-3 supplementation will be given to mothers from pregnancy and lactation while L. reuteri will be given to the mothers during pregnancy and later to the children during the first year of life.The children will be clinically followed by an allergy nurse regularly. Questionnaires regarding data on environment, siblings, pets, breast feeding, smoking exposure, upper respiratory and other infections and clinical symptoms of allergic disease will be filled regularly. Skin prick tests (SPTs) will be performed in the children at 6 and 12 months with milk, egg, wheat, peanut and cat. At 24 months, timothy and birch allergen extracts will be added. A pediatrician will assess the children at 24 months of life and whenever it is needed during the study period. Dietary habits will be assessed during pregnancy (25th gestational week) and 6 months after child birth. Blood samples in the children will be taken from cord blood and at 6, 12 and 24 months of life. Maternal blood samples will be taken at 20th weeks of gestation and at child birth. Milk samples will be collected 1-4 days after partus and monthly during the first 4 months of lactation. Maternal gastrointestinal function will be addressed by validated diary cards. Saliva from the children and fecal samples from mother and child will also be collected according to the following protocol.

Inclusion Criteria:

• pregnant women expecting a child with at least one parent or a sibling with clinical symptoms/history of allergic disease
• breastfeeding for at least 3 months is mandatory for inclusion in the statistical assessment in the study

Exclusion Criteria:

• mothers with fish allergy
• twin pregnancy
• mothers previously/currently using omega-3 PUFA or probiotic dietary supplementation
• children born before gestational week 33 or seriously ill will be excluded from the study.