A pilot study including 50 obese pregnant nulliparous with BMI between 30-35 kg/m2 will, after accepting participation, be randomized to receive daily placebo or probiotics (four capsules of Vivomixx®; total of 450 billion CFU/day) from gestational age 14-20 until delivery. The infants will be followed until 9 months of age. Shortly after birth, tissue composition will be measured in the infants by DEXA-scanning. The women will be monitored by weight, blood-, fecal- and urine samples, diet questionnaires and hospital record review. Vivomixx® is a probiotic mixture of 8 probiotic strains, (Bifidobacterium breve, Bifidobacterium longum, Bifidobacterium infantis, Lactobacillus acidophilus, Lactobacillus plantarum, Lactobacillus paracasei, Lactobacillus bulgaricus and Streptococcus thermophilus).