The aim is to study whether the microbiota of children who are exposed to antibiotics at birth could be modified by synbiotic supplement and thereby reduce the risk of obesity, chronic diseases and respiratory tract infections. A total of 125 mother-child pairs will be recruited in this randomized, double-blind, placebo-controlled study. Infants are randomized to receive either a synbiotic supplement or a placebo for 2 months, after which their growth and morbidity will be monitored at the research clinic for 2 years.