Infants to be enrolled at birth.  Inclusion Criteria for Infants (study subjects)  Gestational age at birth ≥ 37±0 ≤ weeks 42±0 weeks Birthweight more than 2500 g No exposure to oral or intravenous antibiotics No complications that need medical interventions (e.g. respiratory distress symptoms or infections) Both legal guardians provided voluntary written informed consent on behalf of the infant  Pregnant women:  Women age above 18 years at informed consent Singleton pregnancy Uncomplicated pregnancy No use of medication Aim to give birth vaginally and breastfeed No use of probiotics during the last month before estimated birth and until six weeks postpartum Provided voluntary written informed consent  Exclusion criteria for Infants (study subjects)  • Admission to the neonatal intensive care unit (NICU)