In this context, psychomotor outcome (PSO) is assessed at 6, 12, 18 and 24 months ca by means of the Griffiths Mental Development Scales 0-2 years [26]. These scales investigate five main areas (locomotor, personal and social skills, hearing and language, eye and hand coordination, performance), providing a general developmental quotient (DQ) of infant's abilities and five sub-scale quotients (SQ) for each of the developmental areas.