Daily dose of 6x109 UFC Infloran® -Berne, Switzerland- (Bifidobacterium bifidum NCDO 2203 and Lactobacillus acidophilus NCDO 1748) from 7 days of life until reaching a postmenstrual age of 34 weeks or discharge

Untreated control group

Normal neurodevelopment will be considered when no muscle tone changes, no impaired fine or gross motor coordination, Bayley scale score between above 84, no behaviour disorders or visual disability.

Mild impairment will be considered if any of the following: muscle tone changes, impaired fine or gross motor coordination, Bayley scale score between 71-84, moderate behaviour disorders or mild visual disability.

Moderate impairment will be diagnosed when suffering from any of the following: spastic diplegia, hemiplegia, seizures (non-febrile), Bayley scores between 50-70, severe behaviour disorders, moderate visual disability or mild-moderate hypoacusis.

Severe impairment will be attributed to subjects with any of the following: spastic quadriplegia, choreoathetosis, ataxia, Bayley score <50, blindness or severe hypoacusis

Wechsler Intelligence Scale for Children - Fifth edition. Ranges from below 69 to above 130. Scores from 90-109 indicate average, above it indicates above average and below, below average performance.

Child behaviour checklist 6-18 years of age. 113 items about behaviour and social competence scored from 0 "absent" to 2 "occurs often"

cases fulfilling the stage II or above of the modified Bell's Criteria

Proportion of dead participants before discharge