A probiotic (Lactobacillus rhamnosus GG) supplement to pregnant women the last four weeks of pregnancy and three months after birth is expected to give a 40% reduction in risk of atopic sensitisation and allergic disease at two years of age, compared to placebo.

To investigate how probiotics given to pregnant women during the last 4 weeks of pregnancy and the first 4 months after birth influence the establishment and composition of the gut microflora in children from birth until two years of age.

At the same time to investigate the relationship between gut flora composition and the development of the immune system.

To investigate the relationship between supplement of probiotics to pregnant and breast-feeding women, the microbial composition of the gut flora in their children, the development of the childrens' immune system, and the prevalence of atopic sensitisation and atopic disease at two years of age.

Inclusion Criteria:

• All pregnant women understanding Norwegian language and who has signed an informed consent form, can be included.
• Inclusion must take place before week 36 in the pregnancy.
• The woman must plan to breast-feed the first 4 months after birth.
• She must live in Trondheim.

Exclusion Criteria:

• Not being able to fill in the questionnaire in Norwegian language
• Lactose intolerance
• Consumption of probiotics earlier in the pregnancy.
• Intention to move from Trondheim in the next 25 months.
• Pregnant women in risk of eclampsia, or other serious disease that can influence beast-feeding or care for the child.