Objective To assess the incidence of DDH and to evaluate the role of feeding, D vitamin implementation, sex, age and fetal position as predictive factors for the withdrawal of the nucleous of ossification of the femoral head in an unselected population of infants.

Methods 1997 infants aged between 4 and 14 weeks (average age 9.8±1.95 weeks; M/F = 1015/957) studied in a Pediatric Ward between 2006 and 2007 have been recruited. All subjects were examined by ultrasound with Graf’s method; their parents received a questionnaire for anamnestic data.

Results The incidence of pathological cases resulted in agreement with the European data (5%) even if the cases of physiologically immature hip appeared lower compared to these data (4.5%). The average age of nucleous of ossification’s withdrawal was 10.7 weeks.

The presence of the nucleous of ossification was correlated with weight at birth (p = 0.005), weight (p = 0.007) and age at the time of the examination (p = 0.000) and female gender (odds ratio = 2.720), where neither the position during pregnancy, nor the kind of feeding (breast feeding or formulated milk), nor the D vitamin addition seemed to interfere significantly with the hip maturation.

Conclusions Our observations suggest that bone maturation is conditioned by individual constitutional elements, as if bony transformation of cartilagineous nucleous would be, for each subject, determined by previous factors (genetics, hormonal) and therefore less influenced by external elements (nutritonial, mechanical).